000
FXUS63 KILX 060451
AFDILX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LINCOLN IL
1151 PM CDT SUN SEP 5 2010

.DISCUSSION...
ISSUED 857 PM CDT SUN SEP 5 2010

THE WAA FLOWS ALOFT HAVE BECOME VERY EFFICIENT IN UTILIZING ALL
AVAILABLE MOISTURE IN PRECIP PRODUCTION. THE LOW LEVELS REMAIN
RELATIVELY DRY...BUT THE RADAR RETURNS ABOVE 40 DBZ ARE MOST
LIKELY REACHING THE GROUND. LIGHTNING IS ALSO DEVELOPING IN THE
MORE SUBSTANTIAL UPDRAFTS.

THE LATEST RUC AND 4KM MODEL GUIDANCE ARE IN AGREEMENT WITH THE
LARGER SCALE MODELS IN DIMINISHING THE PRECIP QUICKLY AS IT ENTERS
ILLINOIS. STILL...FEEL CONFIDENT ENOUGH THAT SOME PRECIP WILL
REACH OUR CWA TO ADD POPS TO THE GRIDS IN THE NORTHERN CWA THE
REST OF THE NIGHT. LOW CHANCE AND SLIGHT CHANCE ARE
SUFFICIENT...AS MEASURABLE RAIN WILL BE LIMITED. MOST PRECIP THAT
REACHES THE GROUND WILL BE TRACE AMOUNTS.

AN INSULATING CLOUD LAYER WILL HELP KEEP LOW TEMPS UP
TONIGHT...ABOUT 10-15 DEG WARMER THAN LAST NIGHT.

UPDATED THE GRIDS FOR WEATHER...SKY... AND QPF FOR TONIGHT.
UPDATED INFO WILL BE AVAILABLE SHORTLY.

SHIMON

&&

.AVIATION...
ISSUED 1151 PM CDT SUN SEP 5 2010...FOR THE 06Z TAFS

THE LLJ ABOVE 2K FT IS INTENSIFYING...PER WIND PROFILER OBS. THIS
GIVES CONFIDENCE TWRD CONTINUING TO FORECAST LLWS CONDITIONS THE
REST OF THE NIGHT. WILL KEEP IT IN UNTIL 15Z WHEN WIND GUSTS WILL
AGAIN MIX DOWN TO THE SURFACE.

SCATTERED RAIN SHOWERS AND ISOLATED THUNDERSTORMS WILL MOVE ACROSS
THE NORTHERN TAF SITES FOR THE NEXT 4-6 HOURS. WILL INCLUDE A VCTS AT
PIA/BMI TO ACCOUNT FOR ANY NEARBY STORMS...AND ONLY VCSH AT CMI.
RUC AND 4KM MODEL OUTPUT ALL SHOW UPDRAFT STRENGTH SHOULD DIMINISH
THE FARTHER EAST STORMS REACH IN OUR CWA.

SOME VERY GUSTY WINDS DEVELOPED JUST TO OUR NW AT 0307Z IN
MLI...WHERE A 69 MPH WIND GUST OCCURRED. THE DRY LOWER LAYERS SET
THE STAGE FOR EVAPORATIVE COOLING TO CREATE COLD POOL DOWNBURSTS.
THOSE STRONGER SHOWERS APPEAR TO HAVE WEAKENED...AND REMAINED
NORTH OF ALL TAF SITES. CAN NOT RULE OUT SOME VERY GUSTY WINDS
WITH ANY SHOWERS/STORMS TONIGHT.

SHIMON
&&

.PREV DISCUSSION...
ISSUED 302 PM CDT SUN SEP 5 2010

SHORT TERM...TONIGHT THROUGH WEDNESDAY...
SURFACE HIGH HAS MOVED TO THE E...WITH SLY RETURN FLOW UNDERWAY OVER
IL. THE AIRMASS IS STILL QUITE DRY WITH DEWPOINTS IN THE 40S FROM
ERN IL ALL THE WAY DOWN INTO LA/MS. WEAK WARM ADVECTION IN THE MID
LEVELS IS PRODUCING ISOLATED CONVECTION OVER IA THIS AFTERNOON...
BUT EXPECT MOST OF THIS ACTIVITY TO REMAIN TO OUR N TONIGHT...WITH
POPS BELOW SLIGHT CHANCE CATEGORY. MON WILL CONTINUE THE DRY TREND
AS THE SURFACE PRESSURE GRADIENT INCREASES AND CAUSES GUSTY WIND
CONDITIONS. AS DISCUSSED BELOW...THERE WILL BE A HEIGHTENED RISK OF
FIRE DANGER FOR PORTIONS OF SERN IL MON AFTERNOON AND EARLY EVENING.

A STRONG UPPER WAVE NOW MOVING ACROSS THE NRN ROCKIES WILL MOVE INTO
THE NRN PLAINS AND APPROACH THE WRN GREAT LAKES LATE MON NIGHT. THE
ASSOCIATED SURFACE LOW WILL DEEPEN OVER MN BY THAT TIME WITH A COLD
FRONT PUSHING INTO NORTHWESTERN ILLINOIS DURING THE PRE-DAWN HOURS.
EVEN THOUGH LOW LEVEL MOISTURE WILL STILL BE MEAGER...STRONG LIFT
AND ACCOMPANYING MID LEVEL MOISTURE MAY BE SUFFICIENT FOR SCATTERED
STORMS ALONG THE COLD FRONT. WILL PUT IN SOME CHANCE POPS FOR NWRN
IL AFTER MIDNIGHT MON NIGHT AND THEN REDUCE THEM TO SLIGHT CHANCE ON
TUE OVER THE E AS THE BEST LIFT/DYNAMICS MOVE NEWD INTO CANADA.
THERE WILL BE QUITE A TEMPERATURE SPREAD ON TUE WITH HIGHS FROM THE
MID/UPPER 70S NW TO NEAR 90 IN THE FAR SE.

DRY AND COOLER CONDITIONS ARE EXPECTED ON WED AS THE COLD FRONT
CLEARS THE AREA AND WEAK CANADIAN HIGH PRESSURE COMES S IN ITS WAKE.

LONG TERM...THURSDAY THROUGH SUNDAY...

SOME OF THE MODELS BRING A TROPICAL SYSTEM DEVELOPING IN THE WRN
GULF NW AND RETAINING A REMNANT SURFACE LOW AS FAR N AS OK/NRN TX BY
00Z THU. THE RESULTANT INCREASE IN MOISTURE/PCPN OVER THE MIDWEST
LATER THIS WEEK HAS NOT BEEN INCLUDED IN THIS FORECAST DUE TO
UNCERTAINTY IN THE FATE OF THIS SYSTEM THAT FAR IN ADVANCE.

THE TUE COLD FRONT WILL STALL OUT JUST S OF THE STATE AS IT MOVES S
OF THE STRONGER UPPER WESTERLIES. AS THE NEXT SYSTEM COMES INTO THE
PLAINS ON THU...PRESSURE FALLS AND LEE-SIDE TROUGHING WILL BRING THE
FRONT SLOWLY NWD AS A WARM FRONT. MOISTURE WILL BECOME MORE
FAVORABLE AS THE FRONT RETURNS...AND SHOWERS WILL BE POSSIBLE IN THE
ISENTROPIC LIFT AREA N OF THE FRONT OVER IL AS EARLY AS THU. WILL
BEGIN SLIGHT CHANCE POPS OVER THE SW THU WITH INCREASING POPS
SPREADING NE THROUGH THU NIGHT AND FRI. BY SAT...THE UPPER WAVE WILL
BE MOVING ACROSS THE MIDWEST WITH LOW PRESSURE OVER WI AND A COLD
FRONT SWD THROUGH IL. NEXT SUN SHOULD THEN BE DRY BEHIND THE FRONT.

04

&&

.ILX WATCHES/WARNINGS/ADVISORIES...
FIRE WEATHER WATCH FROM MONDAY AFTERNOON THROUGH MONDAY EVENING
FOR ILZ066>068-071>073.

&&

$$

000
FXUS63 KLOT 060354
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
1054 PM CDT SUN SEP 5 2010

.DISCUSSION...
843 PM CDT

TOUCHED UP THE EVENING FORECAST TO INCLUDE A LARGER SWATH OF
PRECIPITATION TO MOVE THROUGH THE AREA. PREVIOUS GUIDANCE TOOK
SHOWERS AND ISOLATED THUNDERSTORMS THAT WERE OVER IOWA...NORTH
AND INTO CENTRAL WISCONSIN. THOUGH FLOW FROM THE SURFACE THROUGH
ABOUT H80 IS OUT OF THE SOUTH TO SOUTHWEST...SUGGESTING MORE OF A
NORTHERLY COMPONENT TO CELL MOVEMENT...WINDS ALOFT /FROM H80 AND
ABOVE/ ARE WEST TO NORTHWEST...AT THE NOSE OF A 100KT JET THAT IS
PUNCHING ACROSS THE CENTRAL PLAINS WITH A WEAK SHORTWAVE BEING
EJECTED OUT AHEAD OF IT. EXPECT THIS WAVE TO CONTINUE TO GLIDE
EAST ACROSS THE CWA THIS EVENING AND EXPECT THE SCATTERED COVERAGE
OF SHOWERS AND A FEW THUNDERSTORMS TO INCREASE OVERNIGHT...REACHING
THE CHICAGOLAND AREA TOWARDS MIDNIGHT. OBSERVATIONAL ANALYSIS
SHOWS THAT ALL OF THE ACTIVITY THAT IS MOVING INTO OUR AREA...IS
ROOTED AOA 6KFT AND IS BEING UNAFFECTED BY THE SOUTHERLY FLOW
BELOW.

SHEA

//PREV DISCUSSION...
324 PM CDT

WARMER WEATHER WILL OCCUR MONDAY.

TONIGHT...SOME SHOWERS MAY REACH ROCKFORD THIS EVENING. THE
SHOWERS AND AN ISOLATED THUNDERSTORM WILL OCCUR THIS EVENING. AT
1948 UTC THERE WERE SHOWERS AND THUNDERSTORMS OVER EASTERN IOWA.
WE EXPECT THE SHOWERS AND THUNDERSTORMS WILL BE NORTH OF
INTERSTATE 80. WARM AIR WILL MOVE NORTH INTO NORTH CENTRAL
ILLINOIS...NORTHEAST ILLINOIS AND NORTHWEST INDIANA TONIGHT. THIS
WARM AIR ADVECTION WILL CONTINUE OVERNIGHT. THE 305 K ISENTROPIC
SURFACE WAS AROUND 10400 FT OR 694 MB THIS MORNING OVER DAVENPORT.
THE OUR LOCAL WRF MODEL FORECAST STRONG ISENTROPIC LIFT ALONG THE
305 K SURFACE LATE TONIGHT AND MONDAY. WE WILL KEEP A CHANCE OF
SHOWERS AND THUNDERSTORMS NORTH OF INTERSTATE 80 TONIGHT. WE USED
A COMBINATION OF MODEL OUTPUT STATISTICS FOR THE TEMPERATURE AND
DEWPOINT FORECASTS. THIS COMBINATION OF MODEL OUTPUT STATISTICS
FROM THE VARIOUS MODELS HAD THE LOWEST MEAN ABSOLUTE ERRORS FOR
THE LAST SEVEN DAYS.

MONDAY...WARM AIR AND MORE HUMID AIR WILL MOVE INTO NORTHERN
ILLINOIS AND NORTHWEST INDIANA. ALTHOUGH MOST OF THE ISENTROPIC
LIFT ON THE 305 K SURFACE WILL BE NORTH OF ILLINOIS. THERE WILL BE
A CHANCE OF SHOWERS AND ISOLATED THUNDERSTORMS NORTH OF ILLINOIS
WISCONSIN BORDER. THE HIGH TEMPERATURE ARE EXPECTED TO BE IN THE
80S.

MONDAY NIGHT THROUGH THURSDAY...A STRONG 500 MB TROUGH THAT WAS
OVER BRITISH COLUMBIA AND ALBERTA WILL MOVE ACROSS THE NORTHERN
GREAT PLAINS MONDAY. THE GFS...CANADIAN...NAM AND ECMWF MODELS
SHOW THE TROUGH MOVING INTO ILLINOIS BY TUESDAY MORNING. MOST OF
THE STRONG POSITIVE VORTICITY ADVECTION WILL BE IN WISCONSIN. THAT
IS WHERE WE EXPECT MOST OF THE LIFT WILL BE. WE WILL HAVE A CHANCE
OF THUNDERSTORMS MONDAY NIGHT AND TUESDAY NORTH OF INTERSTATE 80.
THE WEATHER WILL BE DRY WEDNESDAY WITH COOLER WEATHER. THERE WILL
BE AN INCREASING CHANCE OF THUNDERSTORMS LATE THURSDAY AND FRIDAY.

&&

.FIRE WEATHER...
330 AM CDT

THE ATMOSPHERE MAY APPROACH FIRE WEATHER RED FLAG CONDITIONS MONDAY
AFTERNOON AND EVENING. THAT IS WHEN THE HUMIDITY IS FORECAST TO BE
THE LOWEST. THE RED FLAG CONDITIONS MAY DEPEND ON WIND AND FUEL
MOISTURE. THERE WILL BE GUSTY CONDITIONS BUT THE FUEL MOISTURE
WILL HAVE TO BE WATCHED MONDAY.

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 04Z...

OCCASIONAL GUSTS FROM S TO 20KT BECOME MORE FREQUENT AFT 12Z MON.
LGT SHRA SLIDING OVER TERMINALS...SHUD DIMINISH TO VCSH AFT 06Z.
LLWS INCREASES FROM S/SW ARND 2KFT AGL TO 35KTS.

BEACHLER

//DISCUSSION...UPDATED 04Z...

IR IMAGERY SHOWS AN AREA OF MID/HIGH LVL CLOUDS SLIDING E/NE ALONG
THE LEADING EDGE OF AN ELEVATED BNDRY. ELEVATED INSTABILITY WAS
ASSOCIATED WITH THIS BNDRY AS IT PUSHES OVER NORTHERN IL/SOUTHERN
WI/NORTHWEST IN...RESULTING IN SOME SCT SHRA. NEAR SFC ENVIRONMENT
REMAINS RELATIVELY DRY. LARGER CONCERN OVERNIGHT IS THE
DEVELOPMENT OF LLWS FOR MANY AIRFIELDS. GUIDANCE HAS BACKED OFF OF
EARLIER CONDS OF 45KTS TO CURRENT ANALYSIS OF 35KTS OFF OF THE
DECK ARND 2KFT AGL FROM THE 200-220 DEG. NOT EXPECTING SFC WINDS
TO KICK BACK UP TO GUSTY CONDS UNTIL AFT DAYBREAK MON AS BETTER
MIXING ARRIVES. IT STILL APPEARS THE WIND DIR WILL BE S VEERING
SW BY LATE AFTN. MIXED LYR MON SHUD FILTER TO THE SFC GUSTS BTWN
15-20KTS BY 16Z THEN INCREASE TO 25-30KTS BY 21-22Z. SFC LOW SHUD
TRACK TWRDS UPPER GREAT LAKES AFT 03Z TUE...WITH FRONTAL BNDRY
PASSAGE NOT EXPECTED FOR NORTHERN IL/NORTHWEST IN UNTIL MIDDAY TUE
AT THE EARLIEST.

BEACHLER

//ORD AND MDW CONFIDENCE...UPDATED 04Z...

HIGH CONFIDENCE ON WINDS AND LLWS FORECAST.
MEDIUM CONFIDENCE ON PRECISE TIMING/COVERAGE OF PRECIP.

BEACHLER

//OUTLOOK FOR ORD/MDW FOR 06Z TUESDAY-12Z SATURDAY...UPDATED 18Z...

MONDAY NIGHT...SLIGHT CHANCE TSRA OTHERWISE VFR.
TUESDAY...VFR. WIND GUSTS TO 30 KTS POSSIBLE DURING THE DAY.
WEDNESDAY...VFR.
THURSDAY...SLIGHT CHANCE TSRA OTHERWISE VFR.
FRIDAY...CHANCE TSRA OTHERWISE VFR.
SATURDAY...CHANCE TSRA OTHERWISE VFR.

BMD

&&

.MARINE...
232 PM CDT

A TIGHT PRESSURE GRADIENT PERSISTS TODAY BETWEEN A RIDGE OF HIGH
PRESSURE THAT EXTENDS FROM THE EAST COAST INTO TENNESSEE AND A LOW
PRESSURE SYSTEM OVER THE CENTRAL PLAINS. A WARM FRONT LIFTING ACROSS
THE LAKE THIS EVENING WILL BRING A CHANCE OF SHOWERS AND
THUNDERSTORMS TONIGHT. AS THE COLD FRONT APPROACHES THE AREA
TOMORROW...THE PRESSURE GRADIENT WILL TIGHTEN AND WINDS ARE EXPECTED
TO INCREASE TO GALES BY LATE MONDAY NIGHT/TUESDAY MORNING AND LAST
THROUGH EARLY WEDNESDAY MORNING. WINDS WILL BE SOUTH TO SOUTHWEST
THROUGH THIS PERIOD BEFORE FINALLY COMING AROUND TO THE NORTHWEST
AND GRADUALLY DIMINISHING BEHIND THE COLD FRONT. HIGH PRESSURE THEN
WILL BUILD INTO THE UPPER MIDWEST WEDNESDAY AND BOTH WINDS AND WAVES
WILL SUBSIDE THROUGHOUT THE DAY.

BMD

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY...LMZ740-LMZ741-LMZ742-LMZ743-LMZ744-
     LMZ745...7 AM MONDAY TO 7 AM TUESDAY.

     GALE WATCH...LMZ740-LMZ741-LMZ742-LMZ743-LMZ744-LMZ745...7 AM
     TUESDAY TO 9 PM TUESDAY.

     GALE WATCH...LMZ080-LMZ567-LMZ669-LMZ671-LMZ673-LMZ675-LMZ777-
     LMZ779-LMZ868-LMZ870-LMZ872-LMZ874-LMZ876-LMZ878...MIDNIGHT
     TUESDAY TO 9 PM TUESDAY.

     GALE WATCH...LMZ261-LMZ362-LMZ364-LMZ366-LMZ563-LMZ565...5 AM
     TUESDAY TO 9 PM TUESDAY.

&&

$$

000
FXUS63 KLOT 060316
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
1016 PM CDT SUN SEP 5 2010

.DISCUSSION...
843 PM CDT

TOUCHED UP THE EVENING FORECAST TO INCLUDE A LARGER SWATH OF
PRECIPITATION TO MOVE THROUGH THE AREA. PREVIOUS GUIDANCE TOOK
SHOWERS AND ISOLATED THUNDERSTORMS THAT WERE OVER IOWA...NORTH
AND INTO CENTRAL WISCONSIN. THOUGH FLOW FROM THE SURFACE THROUGH
ABOUT H80 IS OUT OF THE SOUTH TO SOUTHWEST...SUGGESTING MORE OF A
NORTHERLY COMPONENT TO CELL MOVEMENT...WINDS ALOFT /FROM H80 AND
ABOVE/ ARE WEST TO NORTHWEST...AT THE NOSE OF A 100KT JET THAT IS
PUNCHING ACROSS THE CENTRAL PLAINS WITH A WEAK SHORTWAVE BEING
EJECTED OUT AHEAD OF IT. EXPECT THIS WAVE TO CONTINUE TO GLIDE
EAST ACROSS THE CWA THIS EVENING AND EXPECT THE SCATTERED COVERAGE
OF SHOWERS AND A FEW THUNDERSTORMS TO INCREASE OVERNIGHT...REACHING
THE CHICAGOLAND AREA TOWARDS MIDNIGHT. OBSERVATIONAL ANALYSIS
SHOWS THAT ALL OF THE ACTIVITY THAT IS MOVING INTO OUR AREA...IS
ROOTED AOA 6KFT AND IS BEING UNAFFECTED BY THE SOUTHERLY FLOW
BELOW.

SHEA

//PREV DISCUSSION...
324 PM CDT

WARMER WEATHER WILL OCCUR MONDAY.

TONIGHT...SOME SHOWERS MAY REACH ROCKFORD THIS EVENING. THE
SHOWERS AND AN ISOLATED THUNDERSTORM WILL OCCUR THIS EVENING. AT
1948 UTC THERE WERE SHOWERS AND THUNDERSTORMS OVER EASTERN IOWA.
WE EXPECT THE SHOWERS AND THUNDERSTORMS WILL BE NORTH OF
INTERSTATE 80. WARM AIR WILL MOVE NORTH INTO NORTH CENTRAL
ILLINOIS...NORTHEAST ILLINOIS AND NORTHWEST INDIANA TONIGHT. THIS
WARM AIR ADVECTION WILL CONTINUE OVERNIGHT. THE 305 K ISENTROPIC
SURFACE WAS AROUND 10400 FT OR 694 MB THIS MORNING OVER DAVENPORT.
THE OUR LOCAL WRF MODEL FORECAST STRONG ISENTROPIC LIFT ALONG THE
305 K SURFACE LATE TONIGHT AND MONDAY. WE WILL KEEP A CHANCE OF
SHOWERS AND THUNDERSTORMS NORTH OF INTERSTATE 80 TONIGHT. WE USED
A COMBINATION OF MODEL OUTPUT STATISTICS FOR THE TEMPERATURE AND
DEWPOINT FORECASTS. THIS COMBINATION OF MODEL OUTPUT STATISTICS
FROM THE VARIOUS MODELS HAD THE LOWEST MEAN ABSOLUTE ERRORS FOR
THE LAST SEVEN DAYS.

MONDAY...WARM AIR AND MORE HUMID AIR WILL MOVE INTO NORTHERN
ILLINOIS AND NORTHWEST INDIANA. ALTHOUGH MOST OF THE ISENTROPIC
LIFT ON THE 305 K SURFACE WILL BE NORTH OF ILLINOIS. THERE WILL BE
A CHANCE OF SHOWERS AND ISOLATED THUNDERSTORMS NORTH OF ILLINOIS
WISCONSIN BORDER. THE HIGH TEMPERATURE ARE EXPECTED TO BE IN THE
80S.

MONDAY NIGHT THROUGH THURSDAY...A STRONG 500 MB TROUGH THAT WAS
OVER BRITISH COLUMBIA AND ALBERTA WILL MOVE ACROSS THE NORTHERN
GREAT PLAINS MONDAY. THE GFS...CANADIAN...NAM AND ECMWF MODELS
SHOW THE TROUGH MOVING INTO ILLINOIS BY TUESDAY MORNING. MOST OF
THE STRONG POSITIVE VORTICITY ADVECTION WILL BE IN WISCONSIN. THAT
IS WHERE WE EXPECT MOST OF THE LIFT WILL BE. WE WILL HAVE A CHANCE
OF THUNDERSTORMS MONDAY NIGHT AND TUESDAY NORTH OF INTERSTATE 80.
THE WEATHER WILL BE DRY WEDNESDAY WITH COOLER WEATHER. THERE WILL
BE AN INCREASING CHANCE OF THUNDERSTORMS LATE THURSDAY AND FRIDAY.

&&

.FIRE WEATHER...
330 AM CDT

THE ATMOSPHERE MAY APPROACH FIRE WEATHER RED FLAG CONDITIONS MONDAY
AFTERNOON AND EVENING. THAT IS WHEN THE HUMIDITY IS FORECAST TO BE
THE LOWEST. THE RED FLAG CONDITIONS MAY DEPEND ON WIND AND FUEL
MOISTURE. THERE WILL BE GUSTY CONDITIONS BUT THE FUEL MOISTURE
WILL HAVE TO BE WATCHED MONDAY.

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 04Z...

OCCASIONAL GUSTS FROM S TO 20KT BECOME MORE FREQUENT AFT 12Z MON.
LGT SHRA SLIDING OVER TERMINALS...SHUD DIMINISH TO VCSH AFT 06Z.
LLWS INCREASES FROM S/SW ARND 2KFT AGL TO 35KTS

BEACHLER

//DISCUSSION...UPDATED 00Z...

IR IMAGERY SHOWS AN AREA OF MID/HIGH LVL CLOUDS SLIDING E/NE ALONG
THE LEADING EDGE OF AN ELEVATED BNDRY. ELEVATED INSTABILITY WAS
ASSOCIATED WITH THIS BNDRY AS IT PUSHES OVER NORTHERN IL/SOUTHERN
WI/NORTHWEST IN...RESULTING IN SOME SCT SHRA. NEAR SFC ENVIRONMENT
REMAINS RELATIVELY DRY...THUS ONLY THINKING SHRA FOR A FEW HRS
THEN PRECIP SHUD ERODE AND RESULT IN P CLOUDY CONDS WITH CLOUD
DECK ARND 8KFT AGL FEW/SCT. THE LARGER CONCERN OVERNIGHT IS THE
DEVELOPMENT OF LLWS FOR MANY AIRFIELDS. GUIDANCE HAS BACKED OFF OF
EARLIER CONDS OF 45KTS TO CURRENT ANALYSIS OF 35KTS OFF OF THE
DECK ARND 2KFT AGL FROM THE 200-220 DEG RANGE BY 05Z. NOT
EXPECTING SFC WINDS TO KICK BACK UP TO GUSTY CONDS UNTIL AFT
DAYBREAK MON AS BETTER MIXING ARRIVES. IT STILL APPEARS THE DIR
WILL BE S VEERING SW BY LATE AFTN. MIXED LYR MON SHUD FILTER TO
THE SFC GUSTS BTWN 15-20KTS BY 16Z THEN INCREASE TO 25-30KTS BY
21-22Z. SFC LOW SHUD TRACK TWRDS UPPER GREAT LAKES AFT 03Z
TUE...WITH FRONTAL BNDRY PASSAGE NOT EXPECTED FOR NORTHERN
IL/NORTHWEST IN UNTIL MIDDAY TUE AT THE EARLIEST.

BEACHLER

//ORD AND MDW CONFIDENCE...UPDATED 04Z...

HIGH CONFIDENCE ON WINDS AND LLWS FORECAST.
MEDIUM CONFIDENCE ON PRECISE TIMING/COVERAGE OF PRECIP.

BEACHLER

//OUTLOOK FOR ORD/MDW FOR 06Z TUESDAY-12Z SATURDAY...UPDATED 18Z...

MONDAY NIGHT...SLIGHT CHANCE TSRA OTHERWISE VFR.
TUESDAY...VFR. WIND GUSTS TO 30 KTS POSSIBLE DURING THE DAY.
WEDNESDAY...VFR.
THURSDAY...SLIGHT CHANCE TSRA OTHERWISE VFR.
FRIDAY...CHANCE TSRA OTHERWISE VFR.
SATURDAY...CHANCE TSRA OTHERWISE VFR.

BMD

&&

.MARINE...
232 PM CDT

A TIGHT PRESSURE GRADIENT PERSISTS TODAY BETWEEN A RIDGE OF HIGH
PRESSURE THAT EXTENDS FROM THE EAST COAST INTO TENNESSEE AND A LOW
PRESSURE SYSTEM OVER THE CENTRAL PLAINS. A WARM FRONT LIFTING ACROSS
THE LAKE THIS EVENING WILL BRING A CHANCE OF SHOWERS AND
THUNDERSTORMS TONIGHT. AS THE COLD FRONT APPROACHES THE AREA
TOMORROW...THE PRESSURE GRADIENT WILL TIGHTEN AND WINDS ARE EXPECTED
TO INCREASE TO GALES BY LATE MONDAY NIGHT/TUESDAY MORNING AND LAST
THROUGH EARLY WEDNESDAY MORNING. WINDS WILL BE SOUTH TO SOUTHWEST
THROUGH THIS PERIOD BEFORE FINALLY COMING AROUND TO THE NORTHWEST
AND GRADUALLY DIMINISHING BEHIND THE COLD FRONT. HIGH PRESSURE THEN
WILL BUILD INTO THE UPPER MIDWEST WEDNESDAY AND BOTH WINDS AND WAVES
WILL SUBSIDE THROUGHOUT THE DAY.

BMD

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY...LMZ740-LMZ741-LMZ742-LMZ743-LMZ744-
     LMZ745...7 AM MONDAY TO 7 AM TUESDAY.

     GALE WATCH...LMZ740-LMZ741-LMZ742-LMZ743-LMZ744-LMZ745...7 AM
     TUESDAY TO 9 PM TUESDAY.

     GALE WATCH...LMZ080-LMZ567-LMZ669-LMZ671-LMZ673-LMZ675-LMZ777-
     LMZ779-LMZ868-LMZ870-LMZ872-LMZ874-LMZ876-LMZ878...MIDNIGHT
     TUESDAY TO 9 PM TUESDAY.

     GALE WATCH...LMZ261-LMZ362-LMZ364-LMZ366-LMZ563-LMZ565...5 AM
     TUESDAY TO 9 PM TUESDAY.

&&

$$

000
FXUS63 KLOT 060205
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
905 PM CDT SUN SEP 5 2010

.DISCUSSION...
843 PM CDT

TOUCHED UP THE EVENING FORECAST TO INCLUDE A LARGER SWATH OF
PRECIPITATION TO MOVE THROUGH THE AREA. PREVIOUS GUIDANCE TOOK
SHOWERS AND ISOLATED THUNDERSTORMS THAT WERE OVER IOWA...NORTH
AND INTO CENTRAL WISCONSIN. THOUGH FLOW FROM THE SURFACE THROUGH
ABOUT H80 IS OUT OF THE SOUTH TO SOUTHWEST...SUGGESTING MORE OF A
NORTHERLY COMPONENT TO CELL MOVEMENT...WINDS ALOFT /FROM H80 AND
ABOVE/ ARE WEST TO NORTHWEST...AT THE NOSE OF A 100KT JET THAT IS
PUNCHING ACROSS THE CENTRAL PLAINS WITH A WEAK SHORTWAVE BEING
EJECTED OUT AHEAD OF IT. EXPECT THIS WAVE TO CONTINUE TO GLIDE
EAST ACROSS THE CWA THIS EVENING AND EXPECT THE SCATTERED COVERAGE
OF SHOWERS AND A FEW THUNDERSTORMS TO INCREASE OVERNIGHT...REACHING
THE CHICAGOLAND AREA TOWARDS MIDNIGHT. OBSERVATIONAL ANALYSIS
SHOWS THAT ALL OF THE ACTIVITY THAT IS MOVING INTO OUR AREA...IS
ROOTED AOA 6KFT AND IS BEING UNAFFECTED BY THE SOUTHERLY FLOW
BELOW.

SHEA

&&

.PREV DISCUSSION...
324 PM CDT

WARMER WEATHER WILL OCCUR MONDAY.

TONIGHT...SOME SHOWERS MAY REACH ROCKFORD THIS EVENING. THE
SHOWERS AND AN ISOLATED THUNDERSTORM WILL OCCUR THIS EVENING. AT
1948 UTC THERE WERE SHOWERS AND THUNDERSTORMS OVER EASTERN IOWA.
WE EXPECT THE SHOWERS AND THUNDERSTORMS WILL BE NORTH OF
INTERSTATE 80. WARM AIR WILL MOVE NORTH INTO NORTH CENTRAL
ILLINOIS...NORTHEAST ILLINOIS AND NORTHWEST INDIANA TONIGHT. THIS
WARM AIR ADVECTION WILL CONTINUE OVERNIGHT. THE 305 K ISENTROPIC
SURFACE WAS AROUND 10400 FT OR 694 MB THIS MORNING OVER DAVENPORT.
THE OUR LOCAL WRF MODEL FORECAST STRONG ISENTROPIC LIFT ALONG THE
305 K SURFACE LATE TONIGHT AND MONDAY. WE WILL KEEP A CHANCE OF
SHOWERS AND THUNDERSTORMS NORTH OF INTERSTATE 80 TONIGHT. WE USED
A COMBINATION OF MODEL OUTPUT STATISTICS FOR THE TEMPERATURE AND
DEWPOINT FORECASTS. THIS COMBINATION OF MODEL OUTPUT STATISTICS
FROM THE VARIOUS MODELS HAD THE LOWEST MEAN ABSOLUTE ERRORS FOR
THE LAST SEVEN DAYS.

MONDAY...WARM AIR AND MORE HUMID AIR WILL MOVE INTO NORTHERN
ILLINOIS AND NORTHWEST INDIANA. ALTHOUGH MOST OF THE ISENTROPIC
LIFT ON THE 305 K SURFACE WILL BE NORTH OF ILLINOIS. THERE WILL BE
A CHANCE OF SHOWERS AND ISOLATED THUNDERSTORMS NORTH OF ILLINOIS
WISCONSIN BORDER. THE HIGH TEMPERATURE ARE EXPECTED TO BE IN THE
80S.

MONDAY NIGHT THROUGH THURSDAY...A STRONG 500 MB TROUGH THAT WAS
OVER BRITISH COLUMBIA AND ALBERTA WILL MOVE ACROSS THE NORTHERN
GREAT PLAINS MONDAY. THE GFS...CANADIAN...NAM AND ECMWF MODELS
SHOW THE TROUGH MOVING INTO ILLINOIS BY TUESDAY MORNING. MOST OF
THE STRONG POSITIVE VORTICITY ADVECTION WILL BE IN WISCONSIN. THAT
IS WHERE WE EXPECT MOST OF THE LIFT WILL BE. WE WILL HAVE A CHANCE
OF THUNDERSTORMS MONDAY NIGHT AND TUESDAY NORTH OF INTERSTATE 80.
THE WEATHER WILL BE DRY WEDNESDAY WITH COOLER WEATHER. THERE WILL
BE AN INCREASING CHANCE OF THUNDERSTORMS LATE THURSDAY AND FRIDAY.

&&

.FIRE WEATHER...
330 AM CDT

THE ATMOSPHERE MAY APPROACH FIRE WEATHER RED FLAG CONDITIONS MONDAY
AFTERNOON AND EVENING. THAT IS WHEN THE HUMIDITY IS FORECAST TO BE
THE LOWEST. THE RED FLAG CONDITIONS MAY DEPEND ON WIND AND FUEL
MOISTURE. THERE WILL BE GUSTY CONDITIONS BUT THE FUEL MOISTURE
WILL HAVE TO BE WATCHED MONDAY.

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 00Z...

LGT SHRA SLIDING OVER TERMINALS THRU 01Z...PSBL LINGERING VCSH AFT
01Z. LLWS INCREASES FROM S/SW ARND 2KFT AGL TO 35KTS BY 05Z. VFR
CONDS OTHERWISE.

BEACHLER

//DISCUSSION...UPDATED 00Z...

IR IMAGERY SHOWS AN AREA OF MID/HIGH LVL CLOUDS SLIDING E/NE ALONG
THE LEADING EDGE OF AN ELEVATED BNDRY. ELEVATED INSTABILITY WAS
ASSOCIATED WITH THIS BNDRY AS IT PUSHES OVER NORTHERN IL/SOUTHERN
WI/NORTHWEST IN...RESULTING IN SOME SCT SHRA. NEAR SFC ENVIRONMENT
REMAINS RELATIVELY DRY...THUS ONLY THINKING SHRA FOR A FEW HRS
THEN PRECIP SHUD ERODE AND RESULT IN P CLOUDY CONDS WITH CLOUD
DECK ARND 8KFT AGL FEW/SCT. THE LARGER CONCERN OVERNIGHT IS THE
DEVELOPMENT OF LLWS FOR MANY AIRFIELDS. GUIDANCE HAS BACKED OFF OF
EARLIER CONDS OF 45KTS TO CURRENT ANALYSIS OF 35KTS OFF OF THE
DECK ARND 2KFT AGL FROM THE 200-220 DEG RANGE BY 05Z. NOT
EXPECTING SFC WINDS TO KICK BACK UP TO GUSTY CONDS UNTIL AFT
DAYBREAK MON AS BETTER MIXING ARRIVES. IT STILL APPEARS THE DIR
WILL BE S VEERING SW BY LATE AFTN. MIXED LYR MON SHUD FILTER TO
THE SFC GUSTS BTWN 15-20KTS BY 16Z THEN INCREASE TO 25-30KTS BY
21-22Z. SFC LOW SHUD TRACK TWRDS UPPER GREAT LAKES AFT 03Z
TUE...WITH FRONTAL BNDRY PASSAGE NOT EXPECTED FOR NORTHERN
IL/NORTHWEST IN UNTIL MIDDAY TUE AT THE EARLIEST.

BEACHLER

//ORD AND MDW CONFIDENCE...UPDATED 00Z...

MEDIUM CONFIDENCE ON PRECIP ENDING BY 01Z.
HIGH CONFIDENCE ON LLWS DEVELOPING AFT 05Z.
HIGH CONFIDENCE ON GUSTY S/SW SFC WINDS AFT 16Z MON.

BEACHLER

//OUTLOOK FOR ORD/MDW FOR 06Z TUESDAY-12Z SATURDAY...UPDATED 18Z...

MONDAY NIGHT...SLIGHT CHANCE TSRA OTHERWISE VFR.
TUESDAY...VFR. WIND GUSTS TO 30 KTS POSSIBLE DURING THE DAY.
WEDNESDAY...VFR.
THURSDAY...SLIGHT CHANCE TSRA OTHERWISE VFR.
FRIDAY...CHANCE TSRA OTHERWISE VFR.
SATURDAY...CHANCE TSRA OTHERWISE VFR.

BMD

&&

.MARINE...
232 PM CDT

A TIGHT PRESSURE GRADIENT PERSISTS TODAY BETWEEN A RIDGE OF HIGH
PRESSURE THAT EXTENDS FROM THE EAST COAST INTO TENNESSEE AND A LOW
PRESSURE SYSTEM OVER THE CENTRAL PLAINS. A WARM FRONT LIFTING ACROSS
THE LAKE THIS EVENING WILL BRING A CHANCE OF SHOWERS AND
THUNDERSTORMS TONIGHT. AS THE COLD FRONT APPROACHES THE AREA
TOMORROW...THE PRESSURE GRADIENT WILL TIGHTEN AND WINDS ARE EXPECTED
TO INCREASE TO GALES BY LATE MONDAY NIGHT/TUESDAY MORNING AND LAST
THROUGH EARLY WEDNESDAY MORNING. WINDS WILL BE SOUTH TO SOUTHWEST
THROUGH THIS PERIOD BEFORE FINALLY COMING AROUND TO THE NORTHWEST
AND GRADUALLY DIMINISHING BEHIND THE COLD FRONT. HIGH PRESSURE THEN
WILL BUILD INTO THE UPPER MIDWEST WEDNESDAY AND BOTH WINDS AND WAVES
WILL SUBSIDE THROUGHOUT THE DAY.

BMD

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY...LMZ740-LMZ741-LMZ742-LMZ743-LMZ744-
     LMZ745...7 AM MONDAY TO 7 AM TUESDAY.

     GALE WATCH...LMZ740-LMZ741-LMZ742-LMZ743-LMZ744-LMZ745...7 AM
     TUESDAY TO 9 PM TUESDAY.

     GALE WATCH...LMZ080-LMZ567-LMZ669-LMZ671-LMZ673-LMZ675-LMZ777-
     LMZ779-LMZ868-LMZ870-LMZ872-LMZ874-LMZ876-LMZ878...MIDNIGHT
     TUESDAY TO 9 PM TUESDAY.

     GALE WATCH...LMZ261-LMZ362-LMZ364-LMZ366-LMZ563-LMZ565...5 AM
     TUESDAY TO 9 PM TUESDAY.

&&

$$

000
FXUS63 KILX 060157
AFDILX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LINCOLN IL
857 PM CDT SUN SEP 5 2010

.DISCUSSION...
ISSUED 857 PM CDT SUN SEP 5 2010

THE WAA FLOWS ALOFT HAVE BECOME VERY EFFICIENT IN UTILIZING ALL
AVAILABLE MOISTURE IN PRECIP PRODUCTION. THE LOW LEVELS REMAIN
RELATIVELY DRY...BUT THE RADAR RETURNS ABOVE 40 DBZ ARE MOST
LIKELY REACHING THE GROUND. LIGHTNING IS ALSO DEVELOPING IN THE
MORE SUBSTANTIAL UPDRAFTS.

THE LATEST RUC AND 4KM MODEL GUIDANCE ARE IN AGREEMENT WITH THE
LARGER SCALE MODELS IN DIMINISHING THE PRECIP QUICKLY AS IT ENTERS
ILLINOIS. STILL...FEEL CONFIDENT ENOUGH THAT SOME PRECIP WILL
REACH OUR CWA TO ADD POPS TO THE GRIDS IN THE NORTHERN CWA THE
REST OF THE NIGHT. LOW CHANCE AND SLIGHT CHANCE ARE
SUFFICIENT...AS MEASURABLE RAIN WILL BE LIMITED. MOST PRECIP THAT
REACHES THE GROUND WILL BE TRACE AMOUNTS.

AN INSULATING CLOUD LAYER WILL HELP KEEP LOW TEMPS UP
TONIGHT...ABOUT 10-15 DEG WARMER THAN LAST NIGHT.

UPDATED THE GRIDS FOR WEATHER...SKY... AND QPF FOR TONIGHT.
UPDATED INFO WILL BE AVAILABLE SHORTLY.

SHIMON
&&

.AVIATION...
ISSUED 644 PM CDT SUN SEP 5 2010...FOR THE 00Z TAFS

WAA MID CLOUDS ARE PROGRESSING ACROSS OUR CWA...WITH RADAR RETURNS
SHOWING A FEW SPRINKLES MAY BE POSSIBLE. WILL NOT INCLUDE ANY
MENTION OF PRECIP IN THE TAFS...DUE TO THE LACK OF MEASURABLE
PRECIP.

WINDS MAY REMAIN 10KT TO 15KT OVERNIGHT...AS THE PRESSURE GRADIENT
INCREASES IN RESPONSE TO APPROACHING LOW PRESSURE.

LOW LEVEL WIND SHEAR /LLWS/ WILL DEVELOP OVERNIGHT. AS THE SURFACE WINDS
DECOUPLE...AND THE LLJ ALOFT INTENSIFIES... WE EXPECT LLWS FOR
MUCH OF THE NIGHT. THE WESTERN AREAS WILL SEE STRONGER WIND
SHEAR...WITH 40 KTS BY 12Z. THE EASTERN AREAS MAY ONLY SEE 30KT.

STRONG SOUTH WINDS ARE EXPECTED TOMORROW...AS MIXING DEVELOPS IN
THE HEAT OF THE DAY. THERE WILL BE FREQUENT GUSTS TO 25-30KT.

SHIMON
&&

.PREV DISCUSSION...
ISSUED 302 PM CDT SUN SEP 5 2010

SHORT TERM...TONIGHT THROUGH WEDNESDAY...
SURFACE HIGH HAS MOVED TO THE E...WITH SLY RETURN FLOW UNDERWAY OVER
IL. THE AIRMASS IS STILL QUITE DRY WITH DEWPOINTS IN THE 40S FROM
ERN IL ALL THE WAY DOWN INTO LA/MS. WEAK WARM ADVECTION IN THE MID
LEVELS IS PRODUCING ISOLATED CONVECTION OVER IA THIS AFTERNOON...
BUT EXPECT MOST OF THIS ACTIVITY TO REMAIN TO OUR N TONIGHT...WITH
POPS BELOW SLIGHT CHANCE CATEGORY. MON WILL CONTINUE THE DRY TREND
AS THE SURFACE PRESSURE GRADIENT INCREASES AND CAUSES GUSTY WIND
CONDITIONS. AS DISCUSSED BELOW...THERE WILL BE A HEIGHTENED RISK OF
FIRE DANGER FOR PORTIONS OF SERN IL MON AFTERNOON AND EARLY EVENING.

A STRONG UPPER WAVE NOW MOVING ACROSS THE NRN ROCKIES WILL MOVE INTO
THE NRN PLAINS AND APPROACH THE WRN GREAT LAKES LATE MON NIGHT. THE
ASSOCIATED SURFACE LOW WILL DEEPEN OVER MN BY THAT TIME WITH A COLD
FRONT PUSHING INTO NORTHWESTERN ILLINOIS DURING THE PRE-DAWN HOURS.
EVEN THOUGH LOW LEVEL MOISTURE WILL STILL BE MEAGER...STRONG LIFT
AND ACCOMPANYING MID LEVEL MOISTURE MAY BE SUFFICIENT FOR SCATTERED
STORMS ALONG THE COLD FRONT. WILL PUT IN SOME CHANCE POPS FOR NWRN
IL AFTER MIDNIGHT MON NIGHT AND THEN REDUCE THEM TO SLIGHT CHANCE ON
TUE OVER THE E AS THE BEST LIFT/DYNAMICS MOVE NEWD INTO CANADA.
THERE WILL BE QUITE A TEMPERATURE SPREAD ON TUE WITH HIGHS FROM THE
MID/UPPER 70S NW TO NEAR 90 IN THE FAR SE.

DRY AND COOLER CONDITIONS ARE EXPECTED ON WED AS THE COLD FRONT
CLEARS THE AREA AND WEAK CANADIAN HIGH PRESSURE COMES S IN ITS WAKE.

LONG TERM...THURSDAY THROUGH SUNDAY...

SOME OF THE MODELS BRING A TROPICAL SYSTEM DEVELOPING IN THE WRN
GULF NW AND RETAINING A REMNANT SURFACE LOW AS FAR N AS OK/NRN TX BY
00Z THU. THE RESULTANT INCREASE IN MOISTURE/PCPN OVER THE MIDWEST
LATER THIS WEEK HAS NOT BEEN INCLUDED IN THIS FORECAST DUE TO
UNCERTAINTY IN THE FATE OF THIS SYSTEM THAT FAR IN ADVANCE.

THE TUE COLD FRONT WILL STALL OUT JUST S OF THE STATE AS IT MOVES S
OF THE STRONGER UPPER WESTERLIES. AS THE NEXT SYSTEM COMES INTO THE
PLAINS ON THU...PRESSURE FALLS AND LEE-SIDE TROUGHING WILL BRING THE
FRONT SLOWLY NWD AS A WARM FRONT. MOISTURE WILL BECOME MORE
FAVORABLE AS THE FRONT RETURNS...AND SHOWERS WILL BE POSSIBLE IN THE
ISENTROPIC LIFT AREA N OF THE FRONT OVER IL AS EARLY AS THU. WILL
BEGIN SLIGHT CHANCE POPS OVER THE SW THU WITH INCREASING POPS
SPREADING NE THROUGH THU NIGHT AND FRI. BY SAT...THE UPPER WAVE WILL
BE MOVING ACROSS THE MIDWEST WITH LOW PRESSURE OVER WI AND A COLD
FRONT SWD THROUGH IL. NEXT SUN SHOULD THEN BE DRY BEHIND THE FRONT.

04

&&

.ILX WATCHES/WARNINGS/ADVISORIES...
FIRE WEATHER WATCH FROM MONDAY AFTERNOON THROUGH MONDAY EVENING
FOR ILZ066>068-071>073.

&&

$$

000
FXUS63 KLOT 060003
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
703 PM CDT SUN SEP 5 2010

.DISCUSSION...
324 PM CDT

WARMER WEATHER WILL OCCUR MONDAY.

TONIGHT...SOME SHOWERS MAY REACH ROCKFORD THIS EVENING. THE
SHOWERS AND AN ISOLATED THUNDERSTORM WILL OCCUR THIS EVENING. AT
1948 UTC THERE WERE SHOWERS AND THUNDERSTORMS OVER EASTERN IOWA.
WE EXPECT THE SHOWERS AND THUNDERSTORMS WILL BE NORTH OF
INTERSTATE 80. WARM AIR WILL MOVE NORTH INTO NORTH CENTRAL
ILLINOIS...NORTHEAST ILLINOIS AND NORTHWEST INDIANA TONIGHT. THIS
WARM AIR ADVECTION WILL CONTINUE OVERNIGHT. THE 305 K ISENTROPIC
SURFACE WAS AROUND 10400 FT OR 694 MB THIS MORNING OVER DAVENPORT.
THE OUR LOCAL WRF MODEL FORECAST STRONG ISENTROPIC LIFT ALONG THE
305 K SURFACE LATE TONIGHT AND MONDAY. WE WILL KEEP A CHANCE OF
SHOWERS AND THUNDERSTORMS NORTH OF INTERSTATE 80 TONIGHT. WE USED
A COMBINATION OF MODEL OUTPUT STATISTICS FOR THE TEMPERATURE AND
DEWPOINT FORECASTS. THIS COMBINATION OF MODEL OUTPUT STATISTICS
FROM THE VARIOUS MODELS HAD THE LOWEST MEAN ABSOLUTE ERRORS FOR
THE LAST SEVEN DAYS.

MONDAY...WARM AIR AND MORE HUMID AIR WILL MOVE INTO NORTHERN
ILLINOIS AND NORTHWEST INDIANA. ALTHOUGH MOST OF THE ISENTROPIC
LIFT ON THE 305 K SURFACE WILL BE NORTH OF ILLINOIS. THERE WILL BE
A CHANCE OF SHOWERS AND ISOLATED THUNDERSTORMS NORTH OF ILLINOIS
WISCONSIN BORDER. THE HIGH TEMPERATURE ARE EXPECTED TO BE IN THE
80S.

MONDAY NIGHT THROUGH THURSDAY...A STRONG 500 MB TROUGH THAT WAS
OVER BRITISH COLUMBIA AND ALBERTA WILL MOVE ACROSS THE NORTHERN
GREAT PLAINS MONDAY. THE GFS...CANADIAN...NAM AND ECMWF MODELS
SHOW THE TROUGH MOVING INTO ILLINOIS BY TUESDAY MORNING. MOST OF
THE STRONG POSITIVE VORTICITY ADVECTION WILL BE IN WISCONSIN. THAT
IS WHERE WE EXPECT MOST OF THE LIFT WILL BE. WE WILL HAVE A CHANCE
OF THUNDERSTORMS MONDAY NIGHT AND TUESDAY NORTH OF INTERSTATE 80.
THE WEATHER WILL BE DRY WEDNESDAY WITH COOLER WEATHER. THERE WILL
BE AN INCREASING CHANCE OF THUNDERSTORMS LATE THURSDAY AND FRIDAY.

&&

.FIRE WEATHER...
330 AM CDT

THE ATMOSPHERE MAY APPROACH FIRE WEATHER RED FLAG CONDITIONS MONDAY
AFTERNOON AND EVENING. THAT IS WHEN THE HUMIDITY IS FORECAST TO BE
THE LOWEST. THE RED FLAG CONDITIONS MAY DEPEND ON WIND AND FUEL
MOISTURE. THERE WILL BE GUSTY CONDITIONS BUT THE FUEL MOISTURE
WILL HAVE TO BE WATCHED MONDAY.

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 00Z...

LGT SHRA SLIDING OVER TERMINALS THRU 01Z...PSBL LINGERING VCSH AFT
01Z. LLWS INCREASES FROM S/SW ARND 2KFT AGL TO 35KTS BY 05Z. VFR
CONDS OTHERWISE.

BEACHLER

//DISCUSSION...UPDATED 00Z...

IR IMAGERY SHOWS AN AREA OF MID/HIGH LVL CLOUDS SLIDING E/NE ALONG
THE LEADING EDGE OF AN ELEVATED BNDRY. ELEVATED INSTABILITY WAS
ASSOCIATED WITH THIS BNDRY AS IT PUSHES OVER NORTHERN IL/SOUTHERN
WI/NORTHWEST IN...RESULTING IN SOME SCT SHRA. NEAR SFC ENVIRONMENT
REMAINS RELATIVELY DRY...THUS ONLY THINKING SHRA FOR A FEW HRS
THEN PRECIP SHUD ERODE AND RESULT IN P CLOUDY CONDS WITH CLOUD
DECK ARND 8KFT AGL FEW/SCT. THE LARGER CONCERN OVERNIGHT IS THE
DEVELOPMENT OF LLWS FOR MANY AIRFIELDS. GUIDANCE HAS BACKED OFF OF
EARLIER CONDS OF 45KTS TO CURRENT ANALYSIS OF 35KTS OFF OF THE
DECK ARND 2KFT AGL FROM THE 200-220 DEG RANGE BY 05Z. NOT
EXPECTING SFC WINDS TO KICK BACK UP TO GUSTY CONDS UNTIL AFT
DAYBREAK MON AS BETTER MIXING ARRIVES. IT STILL APPEARS THE DIR
WILL BE S VEERING SW BY LATE AFTN. MIXED LYR MON SHUD FILTER TO
THE SFC GUSTS BTWN 15-20KTS BY 16Z THEN INCREASE TO 25-30KTS BY
21-22Z. SFC LOW SHUD TRACK TWRDS UPPER GREAT LAKES AFT 03Z
TUE...WITH FRONTAL BNDRY PASSAGE NOT EXPECTED FOR NORTHERN
IL/NORTHWEST IN UNTIL MIDDAY TUE AT THE EARLIEST.

BEACHLER

//ORD AND MDW CONFIDENCE...UPDATED 00Z...

MEDIUM CONFIDENCE ON PRECIP ENDING BY 01Z.
HIGH CONFIDENCE ON LLWS DEVELOPING AFT 05Z.
HIGH CONFIDENCE ON GUSTY S/SW SFC WINDS AFT 16Z MON.

BEACHLER

//OUTLOOK FOR ORD/MDW FOR 06Z TUESDAY-12Z SATURDAY...UPDATED 18Z...

MONDAY NIGHT...SLIGHT CHANCE TSRA OTHERWISE VFR.
TUESDAY...VFR. WIND GUSTS TO 30 KTS POSSIBLE DURING THE DAY.
WEDNESDAY...VFR.
THURSDAY...SLIGHT CHANCE TSRA OTHERWISE VFR.
FRIDAY...CHANCE TSRA OTHERWISE VFR.
SATURDAY...CHANCE TSRA OTHERWISE VFR.

BMD

&&

.MARINE...
232 PM CDT

A TIGHT PRESSURE GRADIENT PERSISTS TODAY BETWEEN A RIDGE OF HIGH
PRESSURE THAT EXTENDS FROM THE EAST COAST INTO TENNESSEE AND A LOW
PRESSURE SYSTEM OVER THE CENTRAL PLAINS. A WARM FRONT LIFTING ACROSS
THE LAKE THIS EVENING WILL BRING A CHANCE OF SHOWERS AND
THUNDERSTORMS TONIGHT. AS THE COLD FRONT APPROACHES THE AREA
TOMORROW...THE PRESSURE GRADIENT WILL TIGHTEN AND WINDS ARE EXPECTED
TO INCREASE TO GALES BY LATE MONDAY NIGHT/TUESDAY MORNING AND LAST
THROUGH EARLY WEDNESDAY MORNING. WINDS WILL BE SOUTH TO SOUTHWEST
THROUGH THIS PERIOD BEFORE FINALLY COMING AROUND TO THE NORTHWEST
AND GRADUALLY DIMINISHING BEHIND THE COLD FRONT. HIGH PRESSURE THEN
WILL BUILD INTO THE UPPER MIDWEST WEDNESDAY AND BOTH WINDS AND WAVES
WILL SUBSIDE THROUGHOUT THE DAY.

BMD

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY...LMZ740-LMZ741-LMZ742-LMZ743-LMZ744-
     LMZ745...7 AM MONDAY TO 7 AM TUESDAY.

     GALE WATCH...LMZ740-LMZ741-LMZ742-LMZ743-LMZ744-LMZ745...7 AM
     TUESDAY TO 9 PM TUESDAY.

     GALE WATCH...LMZ080-LMZ567-LMZ669-LMZ671-LMZ673-LMZ675-LMZ777-
     LMZ779-LMZ868-LMZ870-LMZ872-LMZ874-LMZ876-LMZ878...MIDNIGHT
     TUESDAY TO 9 PM TUESDAY.

     GALE WATCH...LMZ261-LMZ362-LMZ364-LMZ366-LMZ563-LMZ565...5 AM
     TUESDAY TO 9 PM TUESDAY.

&&

$$

000
FXUS63 KILX 052344
AFDILX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LINCOLN IL
644 PM CDT SUN SEP 5 2010

.DISCUSSION...
ISSUED 302 PM CDT SUN SEP 5 2010

SHORT TERM...TONIGHT THROUGH WEDNESDAY...
SURFACE HIGH HAS MOVED TO THE E...WITH SLY RETURN FLOW UNDERWAY OVER
IL. THE AIRMASS IS STILL QUITE DRY WITH DEWPOINTS IN THE 40S FROM
ERN IL ALL THE WAY DOWN INTO LA/MS. WEAK WARM ADVECTION IN THE MID
LEVELS IS PRODUCING ISOLATED CONVECTION OVER IA THIS AFTERNOON...
BUT EXPECT MOST OF THIS ACTIVITY TO REMAIN TO OUR N TONIGHT...WITH
POPS BELOW SLIGHT CHANCE CATEGORY. MON WILL CONTINUE THE DRY TREND
AS THE SURFACE PRESSURE GRADIENT INCREASES AND CAUSES GUSTY WIND
CONDITIONS. AS DISCUSSED BELOW...THERE WILL BE A HEIGHTENED RISK OF
FIRE DANGER FOR PORTIONS OF SERN IL MON AFTERNOON AND EARLY EVENING.

A STRONG UPPER WAVE NOW MOVING ACROSS THE NRN ROCKIES WILL MOVE INTO
THE NRN PLAINS AND APPROACH THE WRN GREAT LAKES LATE MON NIGHT. THE
ASSOCIATED SURFACE LOW WILL DEEPEN OVER MN BY THAT TIME WITH A COLD
FRONT PUSHING INTO NORTHWESTERN ILLINOIS DURING THE PRE-DAWN HOURS.
EVEN THOUGH LOW LEVEL MOISTURE WILL STILL BE MEAGER...STRONG LIFT
AND ACCOMPANYING MID LEVEL MOISTURE MAY BE SUFFICIENT FOR SCATTERED
STORMS ALONG THE COLD FRONT. WILL PUT IN SOME CHANCE POPS FOR NWRN
IL AFTER MIDNIGHT MON NIGHT AND THEN REDUCE THEM TO SLIGHT CHANCE ON
TUE OVER THE E AS THE BEST LIFT/DYNAMICS MOVE NEWD INTO CANADA.
THERE WILL BE QUITE A TEMPERATURE SPREAD ON TUE WITH HIGHS FROM THE
MID/UPPER 70S NW TO NEAR 90 IN THE FAR SE.

DRY AND COOLER CONDITIONS ARE EXPECTED ON WED AS THE COLD FRONT
CLEARS THE AREA AND WEAK CANADIAN HIGH PRESSURE COMES S IN ITS WAKE.

LONG TERM...THURSDAY THROUGH SUNDAY...

SOME OF THE MODELS BRING A TROPICAL SYSTEM DEVELOPING IN THE WRN
GULF NW AND RETAINING A REMNANT SURFACE LOW AS FAR N AS OK/NRN TX BY
00Z THU. THE RESULTANT INCREASE IN MOISTURE/PCPN OVER THE MIDWEST
LATER THIS WEEK HAS NOT BEEN INCLUDED IN THIS FORECAST DUE TO
UNCERTAINTY IN THE FATE OF THIS SYSTEM THAT FAR IN ADVANCE.

THE TUE COLD FRONT WILL STALL OUT JUST S OF THE STATE AS IT MOVES S
OF THE STRONGER UPPER WESTERLIES. AS THE NEXT SYSTEM COMES INTO THE
PLAINS ON THU...PRESSURE FALLS AND LEE-SIDE TROUGHING WILL BRING THE
FRONT SLOWLY NWD AS A WARM FRONT. MOISTURE WILL BECOME MORE
FAVORABLE AS THE FRONT RETURNS...AND SHOWERS WILL BE POSSIBLE IN THE
ISENTROPIC LIFT AREA N OF THE FRONT OVER IL AS EARLY AS THU. WILL
BEGIN SLIGHT CHANCE POPS OVER THE SW THU WITH INCREASING POPS
SPREADING NE THROUGH THU NIGHT AND FRI. BY SAT...THE UPPER WAVE WILL
BE MOVING ACROSS THE MIDWEST WITH LOW PRESSURE OVER WI AND A COLD
FRONT SWD THROUGH IL. NEXT SUN SHOULD THEN BE DRY BEHIND THE FRONT.

04

&&

.AVIATION...
ISSUED 644 PM CDT SUN SEP 5 2010...FOR THE 00Z TAFS

WAA MID CLOUDS ARE PROGRESSING ACROSS OUR CWA...WITH RADAR RETURNS
SHOWING A FEW SPRINKLES MAY BE POSSIBLE. WILL NOT INCLUDE ANY
MENTION OF PRECIP IN THE TAFS...DUE TO THE LACK OF MEASURABLE
PRECIP.

WINDS MAY REMAIN 10KT TO 15KT OVERNIGHT...AS THE PRESSURE GRADIENT
INCREASES IN RESPONSE TO APPROACHING LOW PRESSURE.

LOW LEVEL WIND SHEAR /LLWS/ WILL DEVELOP OVERNIGHT. AS THE SURFACE WINDS
DECOUPLE...AND THE LLJ ALOFT INTENSIFIES... WE EXPECT LLWS FOR
MUCH OF THE NIGHT. THE WESTERN AREAS WILL SEE STRONGER WIND
SHEAR...WITH 40 KTS BY 12Z. THE EASTERN AREAS MAY ONLY SEE 30KT.

STRONG SOUTH WINDS ARE EXPECTED TOMORROW...AS MIXING DEVELOPS IN
THE HEAT OF THE DAY. THERE WILL BE FREQUENT GUSTS TO 25-30KT.

SHIMON
&&

.ILX WATCHES/WARNINGS/ADVISORIES...
FIRE WEATHER WATCH FROM MONDAY AFTERNOON THROUGH MONDAY EVENING
FOR ILZ066>068-071>073.

&&

$$

000
FXUS63 KLOT 052154
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
454 PM CDT SUN SEP 5 2010

.DISCUSSION...
324 PM CDT

WARMER WEATHER WILL OCCUR MONDAY.

TONIGHT...SOME SHOWERS MAY REACH ROCKFORD THIS EVENING. THE
SHOWERS AND AN ISOLATED THUNDERSTORM WILL OCCUR THIS EVENING. AT
1948 UTC THERE WERE SHOWERS AND THUNDERSTORMS OVER EASTERN IOWA.
WE EXPECT THE SHOWERS AND THUNDERSTORMS WILL BE NORTH OF
INTERSTATE 80. WARM AIR WILL MOVE NORTH INTO NORTH CENTRAL
ILLINOIS...NORTHEAST ILLINOIS AND NORTHWEST INDIANA TONIGHT. THIS
WARM AIR ADVECTION WILL CONTINUE OVERNIGHT. THE 305 K ISENTROPIC
SURFACE WAS AROUND 10400 FT OR 694 MB THIS MORNING OVER DAVENPORT.
THE OUR LOCAL WRF MODEL FORECAST STRONG ISENTROPIC LIFT ALONG THE
305 K SURFACE LATE TONIGHT AND MONDAY. WE WILL KEEP A CHANCE OF
SHOWERS AND THUNDERSTORMS NORTH OF INTERSTATE 80 TONIGHT. WE USED
A COMBINATION OF MODEL OUTPUT STATISTICS FOR THE TEMPERATURE AND
DEWPOINT FORECASTS. THIS COMBINATION OF MODEL OUTPUT STATISTICS
FROM THE VARIOUS MODELS HAD THE LOWEST MEAN ABSOLUTE ERRORS FOR
THE LAST SEVEN DAYS.

MONDAY...WARM AIR AND MORE HUMID AIR WILL MOVE INTO NORTHERN
ILLINOIS AND NORTHWEST INDIANA. ALTHOUGH MOST OF THE ISENTROPIC
LIFT ON THE 305 K SURFACE WILL BE NORTH OF ILLINOIS. THERE WILL BE
A CHANCE OF SHOWERS AND ISOLATED THUNDERSTORMS NORTH OF ILLINOIS
WISCONSIN BORDER. THE HIGH TEMPERATURE ARE EXPECTED TO BE IN THE
80S.

MONDAY NIGHT THROUGH THURSDAY...A STRONG 500 MB TROUGH THAT WAS
OVER BRITISH COLUMBIA AND ALBERTA WILL MOVE ACROSS THE NORTHERN
GREAT PLAINS MONDAY. THE GFS...CANADIAN...NAM AND ECMWF MODELS
SHOW THE TROUGH MOVING INTO ILLINOIS BY TUESDAY MORNING. MOST OF
THE STRONG POSITIVE VORTICITY ADVECTION WILL BE IN WISCONSIN. THAT
IS WHERE WE EXPECT MOST OF THE LIFT WILL BE. WE WILL HAVE A CHANCE
OF THUNDERSTORMS MONDAY NIGHT AND TUESDAY NORTH OF INTERSTATE 80.
THE WEATHER WILL BE DRY WEDNESDAY WITH COOLER WEATHER. THERE WILL
BE AN INCREASING CHANCE OF THUNDERSTORMS LATE THURSDAY AND FRIDAY.

&&

.FIRE WEATHER...
330 AM CDT

THE ATMOSPHERE MAY APPROACH FIRE WEATHER RED FLAG CONDITIONS MONDAY
AFTERNOON AND EVENING. THAT IS WHEN THE HUMIDITY IS FORECAST TO BE
THE LOWEST. THE RED FLAG CONDITIONS MAY DEPEND ON WIND AND FUEL
MOISTURE. THERE WILL BE GUSTY CONDITIONS BUT THE FUEL MOISTURE
WILL HAVE TO BE WATCHED MONDAY.

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 21Z...

PSBL SHRA PUSHING INTO ORD/MDW...FEEL VCSH IS BEST THRU 01Z.
THUNDER SHUD REMAIN EXTREMELY ISOLATED SO HAVE HELD OUT OF TAFS.

GUSTY WINDS BECOME LESS FREQUENT AFT SUNSET...HOWEVER ABOVE THE
DECK ARND 2KFT AGL WINDS INCREASE AFT 03Z TO 45KTS CREATING WIND
SHEAR CONDITIONS. MIXED LYR MON WILL ALLOW GUSTY S/SW WINDS AT THE
SFC.

BEACHLER

//DISCUSSION...UPDATED 18Z...

PRESSURE GRADIENT TIGHTENING OVER THE NEXT 24HRS BETWEEN A RIDGE OF
HIGH PRESSURE OVER THE OHIO RIVER VALLEY AND A DEVELOPING LOW
PRESSURE SYSTEM OVER THE CENTRAL PLAINS. WINDS ARE GRADUALLY
EXPECTED TO BACK TO A MORE SOUTHERLY DIRECTION AND INCREASE IN
MAGNITUDE AS THE PATTERN SHIFTS EAST TODAY. A WEAK WARM FRONT
LIFTING THROUGH THE AREA IS BRINGING A MID LEVEL CLOUD DECK BUT
CONDITIONS SHOULD REMAIN DRY EXPECT FOR AN ISOLATED SPRINKLE OR
SHOWER. AS ATMOSPHERE DECOUPLES LATE TONIGHT...EXPECT LOW LEVEL WIND
SHEAR. STRONG WINDS WILL BE UNABLE TO MIX TO THE SURFACE AND WINDS
AT 2K FT AROUND 40-45KTS ARE EXPECTED WITH UPWARDS OF 50KTS BRIEFLY
POSSIBLE.

MONDAY WILL BE VERY WINDY AGAIN AS COLD FRONT APPROACHES FROM THE
WEST. MAGNITUDE OF WIND GUSTS ARE EXPECTED TO INCREASE THROUGH THE
DAY AS THE DEPTH OF THE MIXED LAYER INCREASES. GUSTS TO AROUND 40KTS
MAY BE POSSIBLE JUST BEYOND THE CURRENT TAF PERIOD.

BMD

//ORD AND MDW CONFIDENCE...UPDATED 21Z...

MEDIUM CONFIDENCE ON VCSH THRU 01Z.
MEDIUM CONFIDENCE IN LLWS AFT 03Z.
HIGH CONFIDENCE ON VFR CONDS.
HIGH CONFIDENCE IN GUSTY S/SW SFC WINDS AFT 15Z MON.

BEACHLER

//OUTLOOK FOR ORD/MDW FOR 06Z TUESDAY-12Z SATURDAY...UPDATED 18Z...

MONDAY NIGHT...SLIGHT CHANCE TSRA OTHERWISE VFR.
TUESDAY...VFR. WIND GUSTS TO 30 KTS POSSIBLE DURING THE DAY.
WEDNESDAY...VFR.
THURSDAY...SLIGHT CHANCE TSRA OTHERWISE VFR.
FRIDAY...CHANCE TSRA OTHERWISE VFR.
SATURDAY...CHANCE TSRA OTHERWISE VFR.

BMD

&&

.MARINE...
232 PM CDT

A TIGHT PRESSURE GRADIENT PERSISTS TODAY BETWEEN A RIDGE OF HIGH
PRESSURE THAT EXTENDS FROM THE EAST COAST INTO TENNESSEE AND A LOW
PRESSURE SYSTEM OVER THE CENTRAL PLAINS. A WARM FRONT LIFTING ACROSS
THE LAKE THIS EVENING WILL BRING A CHANCE OF SHOWERS AND
THUNDERSTORMS TONIGHT. AS THE COLD FRONT APPROACHES THE AREA
TOMORROW...THE PRESSURE GRADIENT WILL TIGHTEN AND WINDS ARE EXPECTED
TO INCREASE TO GALES BY LATE MONDAY NIGHT/TUESDAY MORNING AND LAST
THROUGH EARLY WEDNESDAY MORNING. WINDS WILL BE SOUTH TO SOUTHWEST
THROUGH THIS PERIOD BEFORE FINALLY COMING AROUND TO THE NORTHWEST
AND GRADUALLY DIMINISHING BEHIND THE COLD FRONT. HIGH PRESSURE THEN
WILL BUILD INTO THE UPPER MIDWEST WEDNESDAY AND BOTH WINDS AND WAVES
WILL SUBSIDE THROUGHOUT THE DAY.

BMD

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY...LMZ740-LMZ741-LMZ742-LMZ743-LMZ744-
     LMZ745...7 AM MONDAY TO 7 AM TUESDAY.

     GALE WATCH...LMZ740-LMZ741-LMZ742-LMZ743-LMZ744-LMZ745...7 AM
     TUESDAY TO 9 PM TUESDAY.

     GALE WATCH...LMZ080-LMZ567-LMZ669-LMZ671-LMZ673-LMZ675-LMZ777-
     LMZ779-LMZ868-LMZ870-LMZ872-LMZ874-LMZ876-LMZ878...MIDNIGHT
     TUESDAY TO 9 PM TUESDAY.

     GALE WATCH...LMZ261-LMZ362-LMZ364-LMZ366-LMZ563-LMZ565...5 AM
     TUESDAY TO 9 PM TUESDAY.

&&

$$

000
FXUS63 KLOT 052114
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
414 PM CDT SUN SEP 5 2010

.DISCUSSION...
324 PM CDT

WARMER WEATHER WILL OCCUR MONDAY.

TONIGHT...SOME SHOWERS MAY REACH ROCKFORD THIS EVENING. THE
SHOWERS AND AN ISOLATED THUNDERSTORM WILL OCCUR THIS EVENING. AT
1948 UTC THERE WERE SHOWERS AND THUNDERSTORMS OVER EASTERN IOWA.
WE EXPECT THE SHOWERS AND THUNDERSTORMS WILL BE NORTH OF
INTERSTATE 80. WARM AIR WILL MOVE NORTH INTO NORTH CENTRAL
ILLINOIS...NORTHEAST ILLINOIS AND NORTHWEST INDIANA TONIGHT. THIS
WARM AIR ADVECTION WILL CONTINUE OVERNIGHT. THE 305 K ISENTROPIC
SURFACE WAS AROUND 10400 FT OR 694 MB THIS MORNING OVER DAVENPORT.
THE OUR LOCAL WRF MODEL FORECAST STRONG ISENTROPIC LIFT ALONG THE
305 K SURFACE LATE TONIGHT AND MONDAY. WE WILL KEEP A CHANCE OF
SHOWERS AND THUNDERSTORMS NORTH OF INTERSTATE 80 TONIGHT. WE USED
A COMBINATION OF MODEL OUTPUT STATISTICS FOR THE TEMPERATURE AND
DEWPOINT FORECASTS. THIS COMBINATION OF MODEL OUTPUT STATISTICS
FROM THE VARIOUS MODELS HAD THE LOWEST MEAN ABSOLUTE ERRORS FOR
THE LAST SEVEN DAYS.

MONDAY...WARM AIR AND MORE HUMID AIR WILL MOVE INTO NORTHERN
ILLINOIS AND NORTHWEST INDIANA. ALTHOUGH MOST OF THE ISENTROPIC
LIFT ON THE 305 K SURFACE WILL BE NORTH OF ILLINOIS. THERE WILL BE
A CHANCE OF SHOWERS AND ISOLATED THUNDERSTORMS NORTH OF ILLINOIS
WISCONSIN BORDER. THE HIGH TEMPERATURE ARE EXPECTED TO BE IN THE
80S.

MONDAY NIGHT THROUGH THURSDAY...A STRONG 500 MB TROUGH THAT WAS
OVER BRITISH COLUMBIA AND ALBERTA WILL MOVE ACROSS THE NORTHERN
GREAT PLAINS MONDAY. THE GFS...CANADIAN...NAM AND ECMWF MODELS
SHOW THE TROUGH MOVING INTO ILLINOIS BY TUESDAY MORNING. MOST OF
THE STRONG POSITIVE VORTICITY ADVECTION WILL BE IN WISCONSIN. THAT
IS WHERE WE EXPECT MOST OF THE LIFT WILL BE. WE WILL HAVE A CHANCE
OF THUNDERSTORMS MONDAY NIGHT AND TUESDAY NORTH OF INTERSTATE 80.
THE WEATHER WILL BE DRY WEDNESDAY WITH COOLER WEATHER. THERE WILL
BE AN INCREASING CHANCE OF THUNDERSTORMS LATE THURSDAY AND FRIDAY.

&&

.FIRE WEATHER...
330 AM CDT

THE ATMOSPHERE MAY APPROACH FIRE WEATHER RED FLAG CONDITIONS MONDAY
AFTERNOON AND EVENING. THAT IS WHEN THE HUMIDITY IS FORECAST TO BE
THE LOWEST. THE RED FLAG CONDITIONS MAY DEPEND ON WIND AND FUEL
MOISTURE. THERE WILL BE GUSTY CONDITIONS BUT THE FUEL MOISTURE
WILL HAVE TO BE WATCHED MONDAY.

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 21Z...

GUSTY WINDS BECOME LESS FREQUENT AFT SUNSET...HOWEVER ABOVE THE
DECK ARND 2KFT AGL WINDS INCREASE AFT 03Z TO 45KTS CREATING WIND
SHEAR CONDITIONS. MIXED LYR MON WILL ALLOW GUSTY S/SW WINDS AT THE
SFC.

BEACHLER

//DISCUSSION...UPDATED 18Z...

PRESSURE GRADIENT TIGHTENING OVER THE NEXT 24HRS BETWEEN A RIDGE OF
HIGH PRESSURE OVER THE OHIO RIVER VALLEY AND A DEVELOPING LOW
PRESSURE SYSTEM OVER THE CENTRAL PLAINS. WINDS ARE GRADUALLY
EXPECTED TO BACK TO A MORE SOUTHERLY DIRECTION AND INCREASE IN
MAGNITUDE AS THE PATTERN SHIFTS EAST TODAY. A WEAK WARM FRONT
LIFTING THROUGH THE AREA IS BRINGING A MID LEVEL CLOUD DECK BUT
CONDITIONS SHOULD REMAIN DRY EXPECT FOR AN ISOLATED SPRINKLE OR
SHOWER. AS ATMOSPHERE DECOUPLES LATE TONIGHT...EXPECT LOW LEVEL WIND
SHEAR. STRONG WINDS WILL BE UNABLE TO MIX TO THE SURFACE AND WINDS
AT 2K FT AROUND 40-45KTS ARE EXPECTED WITH UPWARDS OF 50KTS BRIEFLY
POSSIBLE.

MONDAY WILL BE VERY WINDY AGAIN AS COLD FRONT APPROACHES FROM THE
WEST. MAGNITUDE OF WIND GUSTS ARE EXPECTED TO INCREASE THROUGH THE
DAY AS THE DEPTH OF THE MIXED LAYER INCREASES. GUSTS TO AROUND 40KTS
MAY BE POSSIBLE JUST BEYOND THE CURRENT TAF PERIOD.

BMD

//ORD AND MDW CONFIDENCE...UPDATED 21Z...

MEDIUM CONFIDENCE IN LLWS AFT 03Z.
HIGH CONFIDENCE ON VFR CONDS.
HIGH CONFIDENCE IN GUSTY S/SW SFC WINDS AFT 15Z MON.

BEACHLER

//OUTLOOK FOR ORD/MDW FOR 06Z TUESDAY-12Z SATURDAY...UPDATED 18Z...

MONDAY NIGHT...SLIGHT CHANCE TSRA OTHERWISE VFR.
TUESDAY...VFR. WIND GUSTS TO 30 KTS POSSIBLE DURING THE DAY.
WEDNESDAY...VFR.
THURSDAY...SLIGHT CHANCE TSRA OTHERWISE VFR.
FRIDAY...CHANCE TSRA OTHERWISE VFR.
SATURDAY...CHANCE TSRA OTHERWISE VFR.

BMD

&&

.MARINE...
232 PM CDT

A TIGHT PRESSURE GRADIENT PERSISTS TODAY BETWEEN A RIDGE OF HIGH
PRESSURE THAT EXTENDS FROM THE EAST COAST INTO TENNESSEE AND A LOW
PRESSURE SYSTEM OVER THE CENTRAL PLAINS. A WARM FRONT LIFTING ACROSS
THE LAKE THIS EVENING WILL BRING A CHANCE OF SHOWERS AND
THUNDERSTORMS TONIGHT. AS THE COLD FRONT APPROACHES THE AREA
TOMORROW...THE PRESSURE GRADIENT WILL TIGHTEN AND WINDS ARE EXPECTED
TO INCREASE TO GALES BY LATE MONDAY NIGHT/TUESDAY MORNING AND LAST
THROUGH EARLY WEDNESDAY MORNING. WINDS WILL BE SOUTH TO SOUTHWEST
THROUGH THIS PERIOD BEFORE FINALLY COMING AROUND TO THE NORTHWEST
AND GRADUALLY DIMINISHING BEHIND THE COLD FRONT. HIGH PRESSURE THEN
WILL BUILD INTO THE UPPER MIDWEST WEDNESDAY AND BOTH WINDS AND WAVES
WILL SUBSIDE THROUGHOUT THE DAY.

BMD

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY...LMZ740-LMZ741-LMZ742-LMZ743-LMZ744-
     LMZ745...7 AM MONDAY TO 7 AM TUESDAY.

     GALE WATCH...LMZ740-LMZ741-LMZ742-LMZ743-LMZ744-LMZ745...7 AM
     TUESDAY TO 9 PM TUESDAY.

     GALE WATCH...LMZ080-LMZ567-LMZ669-LMZ671-LMZ673-LMZ675-LMZ777-
     LMZ779-LMZ868-LMZ870-LMZ872-LMZ874-LMZ876-LMZ878...MIDNIGHT
     TUESDAY TO 9 PM TUESDAY.

     GALE WATCH...LMZ261-LMZ362-LMZ364-LMZ366-LMZ563-LMZ565...5 AM
     TUESDAY TO 9 PM TUESDAY.

&&

$$

000
FXUS63 KLOT 052051
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
351 PM CDT SUN SEP 5 2010

.DISCUSSION...
324 PM CDT

WARMER WEATHER WILL OCCUR MONDAY.

TONIGHT...SOME SHOWERS MAY REACH ROCKFORD THIS EVENING. THE
SHOWERS AND AN ISOLATED THUNDERSTORM WILL OCCUR THIS EVENING. AT
1948 UTC THERE WERE SHOWERS AND THUNDERSTORMS OVER EASTERN IOWA.
WE EXPECT THE SHOWERS AND THUNDERSTORMS WILL BE NORTH OF
INTERSTATE 80. WARM AIR WILL MOVE NORTH INTO NORTH CENTRAL
ILLINOIS...NORTHEAST ILLINOIS AND NORTHWEST INDIANA TONIGHT. THIS
WARM AIR ADVECTION WILL CONTINUE OVERNIGHT. THE 305 K ISENTROPIC
SURFACE WAS AROUND 10400 FT OR 694 MB THIS MORNING OVER DAVENPORT.
THE OUR LOCAL WRF MODEL FORECAST STRONG ISENTROPIC LIFT ALONG THE
305 K SURFACE LATE TONIGHT AND MONDAY. WE WILL KEEP A CHANCE OF
SHOWERS AND THUNDERSTORMS NORTH OF INTERSTATE 80 TONIGHT. WE USED
A COMBINATION OF MODEL OUTPUT STATISTICS FOR THE TEMPERATURE AND
DEWPOINT FORECASTS. THIS COMBINATION OF MODEL OUTPUT STATISTICS
FROM THE VARIOUS MODELS HAD THE LOWEST MEAN ABSOLUTE ERRORS FOR
THE LAST SEVEN DAYS.

MONDAY...WARM AIR AND MORE HUMID AIR WILL MOVE INTO NORTHERN
ILLINOIS AND NORTHWEST INDIANA. ALTHOUGH MOST OF THE ISENTROPIC
LIFT ON THE 305 K SURFACE WILL BE NORTH OF ILLINOIS. THERE WILL BE
A CHANCE OF SHOWERS AND ISOLATED THUNDERSTORMS NORTH OF ILLINOIS
WISCONSIN BORDER. THE HIGH TEMPERATURE ARE EXPECTED TO BE IN THE
80S.

MONDAY NIGHT THROUGH THURSDAY...A STRONG 500 MB TROUGH THAT WAS
OVER BRITISH COLUMBIA AND ALBERTA WILL MOVE ACROSS THE NORTHERN
GREAT PLAINS MONDAY. THE GFS...CANADIAN...NAM AND ECMWF MODELS
SHOW THE TROUGH MOVING INTO ILLINOIS BY TUESDAY MORNING. MOST OF
THE STRONG POSITIVE VORTICITY ADVECTION WILL BE IN WISCONSIN. THAT
IS WHERE WE EXPECT MOST OF THE LIFT WILL BE. WE WILL HAVE A CHANCE
OF THUNDERSTORMS MONDAY NIGHT AND TUESDAY NORTH OF INTERSTATE 80.
THE WEATHER WILL BE DRY WEDNESDAY WITH COOLER WEATHER. THERE WILL
BE AN INCREASING CHANCE OF THUNDERSTORMS LATE THURSDAY AND FRIDAY.

&&

.FIRE WEATHER...
330 AM CDT

THE ATMOSPHERE MAY APPROACH FIRE WEATHER RED FLAG CONDITIONS MONDAY
AFTERNOON AND EVENING. THAT IS WHEN THE HUMIDITY IS FORECAST TO BE
THE LOWEST. THE RED FLAG CONDITIONS MAY DEPEND ON WIND AND FUEL
MOISTURE. THERE WILL BE GUSTY CONDITIONS BUT THE FUEL MOISTURE
WILL HAVE TO BE WATCHED MONDAY.

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 18Z...

WINDS A LITTLE STRONGER THAN ORIGINALLY ANTICIPATED. BUMPED UP WINDS
ACROSS THE BOARD ADDING GUSTS FOR THIS AFTERNOON. TERMINAL WINDS
VARYING BETWEEN 190-260.

WIND SHEAR CONDITIONS EXPECTED TONIGHT AND STRONG GUSTS ARE
ANTICIPATED ON MONDAY.

BMD

//DISCUSSION...UPDATED 18Z...

PRESSURE GRADIENT TIGHTENING OVER THE NEXT 24HRS BETWEEN A RIDGE OF
HIGH PRESSURE OVER THE OHIO RIVER VALLEY AND A DEVELOPING LOW
PRESSURE SYSTEM OVER THE CENTRAL PLAINS. WINDS ARE GRADUALLY
EXPECTED TO BACK TO A MORE SOUTHERLY DIRECTION AND INCREASE IN
MAGNITUDE AS THE PATTERN SHIFTS EAST TODAY. A WEAK WARM FRONT
LIFTING THROUGH THE AREA IS BRINGING A MID LEVEL CLOUD DECK BUT
CONDITIONS SHOULD REMAIN DRY EXPECT FOR AN ISOLATED SPRINKLE OR
SHOWER. AS ATMOSPHERE DECOUPLES LATE TONIGHT...EXPECT LOW LEVEL WIND
SHEAR. STRONG WINDS WILL BE UNABLE TO MIX TO THE SURFACE AND WINDS
AT 2K FT AROUND 40-45KTS ARE EXPECTED WITH UPWARDS OF 50KTS BRIEFLY
POSSIBLE.

MONDAY WILL BE VERY WINDY AGAIN AS COLD FRONT APPROACHES FROM THE
WEST. MAGNITUDE OF WIND GUSTS ARE EXPECTED TO INCREASE THROUGH THE
DAY AS THE DEPTH OF THE MIXED LAYER INCREASES. GUSTS TO AROUND 40KTS
MAY BE POSSIBLE JUST BEYOND THE CURRENT TAF PERIOD.

BMD

//ORD AND MDW CONFIDENCE...UPDATED 18Z...

HIGH CONFIDENCE IN LOW LEVEL WIND SHEAR TONIGHT.

HIGH CONFIDENCE IN VFR CONDITIONS.

MEDIUM CONFIDENCE IN MAGNITUDE OF WIND GUSTS MONDAY.

BMD

//OUTLOOK FOR ORD/MDW FOR 06Z TUESDAY-12Z SUNDAY...UPDATED 18Z...

MONDAY NIGHT...SLIGHT CHANCE TSRA OTHERWISE VFR.
TUESDAY...VFR. WIND GUSTS TO 30 KTS POSSIBLE DURING THE DAY.
WEDNESDAY...VFR.
THURSDAY...SLIGHT CHANCE TSRA OTHERWISE VFR.
FRIDAY...CHANCE TSRA OTHERWISE VFR.
SATURDAY...CHANCE TSRA OTHERWISE VFR.

BMD

&&

.MARINE...
232 PM CDT

A TIGHT PRESSURE GRADIENT PERSISTS TODAY BETWEEN A RIDGE OF HIGH
PRESSURE THAT EXTENDS FROM THE EAST COAST INTO TENNESSEE AND A LOW
PRESSURE SYSTEM OVER THE CENTRAL PLAINS. A WARM FRONT LIFTING ACROSS
THE LAKE THIS EVENING WILL BRING A CHANCE OF SHOWERS AND
THUNDERSTORMS TONIGHT. AS THE COLD FRONT APPROACHES THE AREA
TOMORROW...THE PRESSURE GRADIENT WILL TIGHTEN AND WINDS ARE EXPECTED
TO INCREASE TO GALES BY LATE MONDAY NIGHT/TUESDAY MORNING AND LAST
THROUGH EARLY WEDNESDAY MORNING. WINDS WILL BE SOUTH TO SOUTHWEST
THROUGH THIS PERIOD BEFORE FINALLY COMING AROUND TO THE NORTHWEST
AND GRADUALLY DIMINISHING BEHIND THE COLD FRONT. HIGH PRESSURE THEN
WILL BUILD INTO THE UPPER MIDWEST WEDNESDAY AND BOTH WINDS AND WAVES
WILL SUBSIDE THROUGHOUT THE DAY.

BMD

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY...LMZ740-LMZ741-LMZ742-LMZ743-LMZ744-
     LMZ745...7 AM MONDAY TO 7 AM TUESDAY.

     GALE WATCH...LMZ740-LMZ741-LMZ742-LMZ743-LMZ744-LMZ745...7 AM
     TUESDAY TO 9 PM TUESDAY.

     GALE WATCH...LMZ080-LMZ567-LMZ669-LMZ671-LMZ673-LMZ675-LMZ777-
     LMZ779-LMZ868-LMZ870-LMZ872-LMZ874-LMZ876-LMZ878...MIDNIGHT
     TUESDAY TO 9 PM TUESDAY.

     GALE WATCH...LMZ261-LMZ362-LMZ364-LMZ366-LMZ563-LMZ565...5 AM
     TUESDAY TO 9 PM TUESDAY.

&&

$$

000
FXUS63 KILX 052003
AFDILX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LINCOLN IL
302 PM CDT SUN SEP 5 2010

.DISCUSSION...
ISSUED 302 PM CDT SUN SEP 5 2010

SHORT TERM...TONIGHT THROUGH WEDNESDAY...
SURFACE HIGH HAS MOVED TO THE E...WITH SLY RETURN FLOW UNDERWAY OVER
IL. THE AIRMASS IS STILL QUITE DRY WITH DEWPOINTS IN THE 40S FROM
ERN IL ALL THE WAY DOWN INTO LA/MS. WEAK WARM ADVECTION IN THE MID
LEVELS IS PRODUCING ISOLATED CONVECTION OVER IA THIS AFTERNOON...
BUT EXPECT MOST OF THIS ACTIVITY TO REMAIN TO OUR N TONIGHT...WITH
POPS BELOW SLIGHT CHANCE CATEGORY. MON WILL CONTINUE THE DRY TREND
AS THE SURFACE PRESSURE GRADIENT INCREASES AND CAUSES GUSTY WIND
CONDITIONS. AS DISCUSSED BELOW...THERE WILL BE A HEIGHTENED RISK OF
FIRE DANGER FOR PORTIONS OF SERN IL MON AFTERNOON AND EARLY EVENING.

A STRONG UPPER WAVE NOW MOVING ACROSS THE NRN ROCKIES WILL MOVE INTO
THE NRN PLAINS AND APPROACH THE WRN GREAT LAKES LATE MON NIGHT. THE
ASSOCIATED SURFACE LOW WILL DEEPEN OVER MN BY THAT TIME WITH A COLD
FRONT PUSHING INTO NORTHWESTERN ILLINOIS DURING THE PRE-DAWN HOURS.
EVEN THOUGH LOW LEVEL MOISTURE WILL STILL BE MEAGER...STRONG LIFT
AND ACCOMPANYING MID LEVEL MOISTURE MAY BE SUFFICIENT FOR SCATTERED
STORMS ALONG THE COLD FRONT. WILL PUT IN SOME CHANCE POPS FOR NWRN
IL AFTER MIDNIGHT MON NIGHT AND THEN REDUCE THEM TO SLIGHT CHANCE ON
TUE OVER THE E AS THE BEST LIFT/DYNAMICS MOVE NEWD INTO CANADA.
THERE WILL BE QUITE A TEMPERATURE SPREAD ON TUE WITH HIGHS FROM THE
MID/UPPER 70S NW TO NEAR 90 IN THE FAR SE.

DRY AND COOLER CONDITIONS ARE EXPECTED ON WED AS THE COLD FRONT
CLEARS THE AREA AND WEAK CANADIAN HIGH PRESSURE COMES S IN ITS WAKE.

LONG TERM...THURSDAY THROUGH SUNDAY...

SOME OF THE MODELS BRING A TROPICAL SYSTEM DEVELOPING IN THE WRN
GULF NW AND RETAINING A REMNANT SURFACE LOW AS FAR N AS OK/NRN TX BY
00Z THU. THE RESULTANT INCREASE IN MOISTURE/PCPN OVER THE MIDWEST
LATER THIS WEEK HAS NOT BEEN INCLUDED IN THIS FORECAST DUE TO
UNCERTAINTY IN THE FATE OF THIS SYSTEM THAT FAR IN ADVANCE.

THE TUE COLD FRONT WILL STALL OUT JUST S OF THE STATE AS IT MOVES S
OF THE STRONGER UPPER WESTERLIES. AS THE NEXT SYSTEM COMES INTO THE
PLAINS ON THU...PRESSURE FALLS AND LEE-SIDE TROUGHING WILL BRING THE
FRONT SLOWLY NWD AS A WARM FRONT. MOISTURE WILL BECOME MORE
FAVORABLE AS THE FRONT RETURNS...AND SHOWERS WILL BE POSSIBLE IN THE
ISENTROPIC LIFT AREA N OF THE FRONT OVER IL AS EARLY AS THU. WILL
BEGIN SLIGHT CHANCE POPS OVER THE SW THU WITH INCREASING POPS
SPREADING NE THROUGH THU NIGHT AND FRI. BY SAT...THE UPPER WAVE WILL
BE MOVING ACROSS THE MIDWEST WITH LOW PRESSURE OVER WI AND A COLD
FRONT SWD THROUGH IL. NEXT SUN SHOULD THEN BE DRY BEHIND THE FRONT.

04
&&

.AVIATION...
ISSUED 1236 PM CDT SUN SEP 5 2010

PATCHY MID CLOUDS CURRENTLY ACROSS IOWA AND NORTHERN MISSOURI WILL
DRIFT EASTWARD INTO CENTRAL ILLINOIS THIS AFTERNOON AND EVE...MAINLY
IMPACTING THE WESTERN TERMINALS. BASED ON FORECAST SOUNDINGS AND
UPSTREAM OBS...CLOUD BASES WILL GENERALLY REMAIN AOA 12000FT. AS
MID-LEVEL WARM ADVECTION INCREASES THIS EVENING...SOME OF THE MODELS
ARE SUGGESTING A FEW SPRINKLES OR LIGHT SHOWERS WILL DEVELOP ACROSS
WEST-CENTRAL AND NORTHWEST ILLINOIS. THINK THESE WILL BE ISOLATED IN
NATURE IF THEY OCCUR AT ALL...SO HAVE NOT INCLUDED VCSH AT ANY OF
THE TAF SITES. GUSTY S/SE WINDS THIS AFTERNOON WILL DIMINISH AFTER
SUNSET...HOWEVER LOW-LEVEL JET WILL INCREASE MARKEDLY. AS A
RESULT...HAVE INCLUDED WIND SHEAR ACROSS THE ENTIRE AREA...WITH 40KT
AT 2000FT ACROSS THE WESTERN SITES TAPERING DOWN TO 30KT AT KCMI. AS
THIS WIND ENERGY GETS MIXED DOWN MONDAY MORNING...SURFACE WINDS WILL
GUST TO 20 TO 25KT...AND PERHAPS EVEN HIGHER BY AFTERNOON.

BARNES
&&

.FIRE WEATHER...
ISSUED 300 PM CDT SUN SEP 5 2010

THE COMBINATION OF DRY AIR AND STRONG WINDS WILL PRODUCE HEIGHTENED
FIRE DANGER OVER PORTIONS OF CENTRAL AND SERN IL ON LABOR DAY. AREAS
SE OF I-70 HAVE MISSED OUT ON THE RECENT HEAVY RAINFALL THAT WAS
EXPERIENCED FURTHER TO THE NW...SO RED FLAG CONDITIONS MAY BE MET OR
EXCEEDED. THE US FORESTRY SERVICE INDICATES THAT 10-HOUR FUELS ARE
AROUND 7 PERCENT...AND LOWEST RELATIVE HUMIDITIES WILL BE AT OR
BELOW 25 PERCENT. IN ADDITION...WINDY CONDITIONS ARE EXPECTED WITH S
WINDS OF 15 TO 25 MPH WITH HIGHER GUSTS. AFTER COORDINATION WITH
PAH/IND...WILL ISSUE A FIRE WEATHER WATCH FOR THE FAR SERN COUNTIES
OF THE FORECAST AREA FOR MON AFTERNOON AND EARLY EVENING.

04
&&

.ILX WATCHES/WARNINGS/ADVISORIES...
FIRE WEATHER WATCH MONDAY AFTERNOON AND EARLY EVENING FOR
ILZ066>068-071>073.

&&

$$

000
FXUS63 KLOT 051933
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
233 PM CDT SUN SEP 5 2010

.DISCUSSION...
339 AM CDT

WHILE CHANCES OF ANY APPRECIABLE PRECIPITATION ARE RATHER LOW FOR
THE LOCAL AREA OVER THE NEXT SEVERAL DAYS...PATTERN WILL BE FAIRLY
ACTIVE IN TERMS OF A VIGOROUS STORM SYSTEM TRACKING JUST NORTH OF
THE AREA THAT WILL BRING SOME MODERATING TEMPERATURES FOR MONDAY
AHEAD OF THE COLD FRONT...AND SOME WINDY CONDITIONS FOR MONDAY AND
TUESDAY.

IN THE NEAR TERM...QUIET WEATHER CONTINUES FOR THE LOCAL AREA AND
THE MOST INTERESTING WEATHER FEATURE TO WATCH FOR TODAY WILL BE MID
LEVEL CLOUDS INCREASING ACROSS THE AREA. IR SATELLITE IMAGERY OVER
PAST 1 TO 2 HOURS BEGINNING TO SHOW BLOSSOMING MID LEVEL CLOUD FROM
SOUTHWEST MINNESOTA INTO SOUTHEAST IOWA AT NOSE OF STRONGER MID
LEVEL WARM ADVECTION. MODELS SEEM TO HAVE HANDLED THIS INCREASING
MID LEVEL RH FAIRLY WELL THIS MORNING...AND SHOULD GRADUALLY SEE THIS
EXPANDING MID DECK WORK ITS WAY INTO NORTHERN ILLINOIS LATER THIS
MORNING AND THIS AFTERNOON.

SOME UPPER FORCING TO INCREASE ACROSS THE AREA THIS AFTERNOON AS A
VORT MAX ACROSS EASTERN SOUTH DAKOTA/EASTERN NEBRASKA PROGRESSES
THOUGH THE UPPER RIDGE AND INTO NORTHERN ILLINOIS. AS THIS
OCCURS...ISENTROPIC UPGLIDE WILL RAMP UP...ESPECIALLY TOWARD
EVENING. ANALYSIS OF NAM/GFS 305K ISENTROPIC SURFACES STILL
INDICATING THIS STRONGEST UPGLIDE ACROSS APPROX NORTHERN ONE
THIRD OF THE FORECAST AREA. EVEN WITH THIS UPGLIDE...CONDENSATIONAL
PRESSURE DEFICITS ON THIS SURFACE STILL 100-150 MB...WITH THE
LOWER VALUES FURTHER TO NORTH FROM CENTRAL WISCONSIN INTO CENTRAL
LOWER MICHIGAN. PRECIPITATION PROB STILL LOOKING QUITE MEAGER
TODAY. EVEN THOUGH SOUTHERLY LOW LEVEL FLOW WILL RAMP UP LATER
THIS AFTERNOON...UPSTREAM MOISTURE PROFILES PER 00Z RAOBS FROM
LAST EVENING ARE NOTHING IMPRESSIVE WITH 850 HPA DEW PTS OF -2 DEG
CELSIUS AT KLZK AND +5 DEG CELSIUS AT KSGF. GIVEN STRENGTH OF
ISENTROPIC UPGLIDE...DID NOT WANT TO COMPLETELY REMOVE POPS FOR
TONIGHT...ALTHOUGH WITH SUCH DRY LOW LEVELS WILL TONE DOWN MENTION
TO SLIGHT CHANCE OF LIGHT RAIN SHOWERS OR SPRINKLES. EXPECTING
TEMPERATURES TODAY TO BE 5 TO 10 DEGREES WARMER THAN YESTERDAY AND
THE MAGNITUDE OF MODERATION TODAY WILL BE SOMEWHAT CONTROLLED BY
EXTENT AND TIMING OF MID LEVEL CLOUD INCREASE THIS AFTERNOON.

BY 12Z MONDAY...FOCUS FOR STRONGER ISENTROPIC LIFT WILL SHIFT
NORTHWARD INTO SOUTHERN/CENTRAL WISCONSIN WITH LOW LEVEL WARM FRONT...
SO HAVE MADE NO CHANGES TO A DRY MONDAY FORECAST AS SOME OF THAT
FAIRLY DRY LOW LEVEL AIR CURRENTLY ACROSS LOWER MS RIVER VALLEY
ADVECTS NORTHWARD. MAIN AXIS OF MOISTURE TRANSPORT MONDAY WILL
OCCUR TO THE WEST ACROSS THE CENTRAL AND NORTHERN PLAINS AS
THE VIGOROUS UPPER LEVEL TROUGH TRACKS EAST OUT OF THE ROCKIES.
WITH LOW LEVEL RIDGE ACROSS LOWER MS RVR VALLEY BEING SLOW TO
TRUDGE EASTWARD...IT STILL APPEARS AS THOUGH MORE SIGNIFICANT LOW
LEVEL MOISTURE WILL BE CONFINED TO NARROW FRONTAL AXIS ONCE AGAIN
AND ANY CHANCE OF PRECIP FOR LOCAL AREA WILL HOLD OFF UNTIL MONDAY
NIGHT AS FRONT APPROACHES. OTHERWISE...MONDAY LOOKING TO BE QUITE
WARM WITH ABOVE NORMAL HIGHS REACHING INTO THE LOWER TO MID 80S
FOR THE AREA WITH SOUTH GUSTS OF 30 TO 35 MPH POSSIBLE IN THE
AFTERNOON. MODELS ARE IN GENERAL AGREEMENT IN OCCLUDING SYSTEM
MONDAY NIGHT INTO EARLY TUESDAY WITH INITIALLY BETTER UPPER
DYNAMICS/LOW LEVEL CONVG MONDAY AFTERNOON/EARLY EVENING SETTING UP
ACROSS PORTIONS OF IOWA/SOUTHERN MINNESOTA. AT THIS TIME...STILL
FEEL BETTER CONVECTIVE CHANCES WILL BE GENERALLY WEST OF MS
RIVER...ALTHOUGH WILL MAINTAIN SLIGHT CHANCE POPS FOR THUNDER FROM
WEST TO EAST MONDAY NIGHT.

SYSTEM WILL SLOWLY FILL TUESDAY AS DRY LOW/MID LEVEL AIR WORKS
INTO THE AREA. THERE MAY BE SOME ISOLD SHOWERS ALONG THE FRONT
EARLY TUESDAY ACROSS SOUTHEASTERN PORTIONS OF THE AREA...BUT
OVERWHELMING DRY AIR ADVECTION ACROSS THE AREA SHOULD RESULT IN
DRY AND VERY WINDY CONDITIONS FOR TUES AFTERNOON. COLD ADVECTION
TUESDAY AFTERNOON WILL ALLOW FOR MORE SUBSTANTIAL MIXED LAYER
DEPTHS AND EVEN SOME CONCERN FOR NUDGING UP AGAINST WIND ADVISORY
CRITERIA AND WILL INCLUDE MENTION OF THESE EXPECTED VERY WINDY
CONDITIONS IN THIS MORNINGS HWO. TEMPS RATHER TRICKY ON TUESDAY
WITH COLD ADVECTION FIGHTING THE EFFECTS OF DEEPER MIXING. MAY BE
A BIT WARM WITH HIGHS TUESDAY RANGING FROM MID 70S FAR NORTH
CENTRAL ILLINOIS TO LOWER 80S FAR SOUTHEAST...BUT THIS DOES APPEAR
TO BE A COMMON SETUP WHEN THE EFFECTS OF SUBSIDENCE/MIXING DO
ALLOW FOR WARMER THAN EXPECTED TEMPS...SO HAVE NOT CHANGED THESE
HIGHS MUCH AT THIS POINT WITH STILL SOME SUBTLE MODEL DIFFERENCES
IN TIMING THIS COLD ADVECTION.

WEATHER TO FINALLY QUIET DOWN TUESDAY NIGHT INTO WEDNESDAY AS NEXT
SFC HIGH SLIDES INTO THE REGION. LOW LEVEL FRONT NOT EXPECTED TO BE
TOO FAR SOUTH OF THE AREA...ALTHOUGH NOT EXPECTING THIS LOW LEVEL
BAROCLINIC ZONE TO BE ACTIVE WITH ANY PRECIP DUE TO LIMITED
MOISTURE. NEW MEDIUM RANGE MODELS STILL SUPPORT THE GOING EXTENDED
FORECAST OF CHANCES OF THUNDER LATE THURSDAY/FRIDAY WITH RENEWED
THETA-E ADVECTION IN ADVANCE OF NEXT SIGNIFICANT UPPER TROUGH
WORKING THROUGH NWRN CONUS. THIS PATTERN SHOULD ALSO ALLOW MUCH OF
THE AREA TO POTENTIALLY WARM BACK INTO THE LOWER 80S TOWARD THE END
OF THE WEEK.

MARSILI

&&

.FIRE WEATHER...
330 AM CDT

SFC PRESSURE GRADIENT WILL STRENGTHEN ON MONDAY AS STRONG SFC LOW
MOVES INTO SOUTHERN MINNESOTA. STILL SOME UNCERTAINTY REMAINS AS
TO MIXING HEIGHTS MONDAY AFTERNOON AND EXACTLY HOW MUCH LOW LEVEL
DRY AIR CAN MIX DOWN TO THE SURFACE. FORECASTED HIGHS INTO THE
LOWER TO MID 80S COMBINED WITH DEW PTS LIKELY MIXING OUT TO AROUND
50 WOULD SUPPORT MIN AFTERNOON RELATIVE HUMIDITIES AROUND 30
PERCENT. WHILE WIND GUSTS SHOULD BE UP AROUND 30 MPH MONDAY
AFTERNOON...ENOUGH UNCERTAINTY EXISTS WITH REGARDS TO MIXING AND
FUEL MOISTURES TO HOLD OFF ON ANY FIRE WEATHER HEADLINES AT THIS
TIME.

TUESDAY IS SHAPING UP AS ANOTHER DAY OF POTENTIAL FIRE WEATHER
CONCERN AS CONFIDENCE IN DEEPER MIXED LAYER IS HIGHER ALONG WITH
POTENTIAL OF SOME SOUTHWEST WIND GUSTS TO 40 TO 45 MPH. IN
CONTRAST TO MONDAY THE MAIN ELEMENT OF UNCERTAINTY WITH HOW LOW
AFTERNOON RELATIVE HUMIDITIES CAN REACH IS JUST HOW HIGH THE
TEMPERATURE WILL CLIMB. AT THIS TIME...HAVE FORECASTED MIN
AFTERNOON RELATIVE HUMIDITIES IN THE 30 TO 35 PERCENT RANGE BUT
THIS WILL NEED TO BE MONITORED FOR ANY CHANGES TO FUTURE
FORECASTS. ALSO IF FRONTAL PASSAGE DOES COME THROUGH DRY MONDAY
NIGHT INTO TUESDAY...FUEL MOISTURES WILL BE SOMEWHAT LOWER WHICH
WOULD INCREASE FIRE WEATHER RISK FOR TUESDAY.

MARSILI

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 18Z...

WINDS A LITTLE STRONGER THAN ORIGINALLY ANTICIPATED. BUMPED UP WINDS
ACROSS THE BOARD ADDING GUSTS FOR THIS AFTERNOON. TERMINAL WINDS
VARYING BETWEEN 190-260.

WIND SHEAR CONDITIONS EXPECTED TONIGHT AND STRONG GUSTS ARE
ANTICIPATED ON MONDAY.

BMD

//DISCUSSION...UPDATED 18Z...

PRESSURE GRADIENT TIGHTENING OVER THE NEXT 24HRS BETWEEN A RIDGE OF
HIGH PRESSURE OVER THE OHIO RIVER VALLEY AND A DEVELOPING LOW
PRESSURE SYSTEM OVER THE CENTRAL PLAINS. WINDS ARE GRADUALLY
EXPECTED TO BACK TO A MORE SOUTHERLY DIRECTION AND INCREASE IN
MAGNITUDE AS THE PATTERN SHIFTS EAST TODAY. A WEAK WARM FRONT
LIFTING THROUGH THE AREA IS BRINGING A MID LEVEL CLOUD DECK BUT
CONDITIONS SHOULD REMAIN DRY EXPECT FOR AN ISOLATED SPRINKLE OR
SHOWER. AS ATMOSPHERE DECOUPLES LATE TONIGHT...EXPECT LOW LEVEL WIND
SHEAR. STRONG WINDS WILL BE UNABLE TO MIX TO THE SURFACE AND WINDS
AT 2K FT AROUND 40-45KTS ARE EXPECTED WITH UPWARDS OF 50KTS BRIEFLY
POSSIBLE.

MONDAY WILL BE VERY WINDY AGAIN AS COLD FRONT APPROACHES FROM THE
WEST. MAGNITUDE OF WIND GUSTS ARE EXPECTED TO INCREASE THROUGH THE
DAY AS THE DEPTH OF THE MIXED LAYER INCREASES. GUSTS TO AROUND 40KTS
MAY BE POSSIBLE JUST BEYOND THE CURRENT TAF PERIOD.

BMD

//ORD AND MDW CONFIDENCE...UPDATED 18Z...

HIGH CONFIDENCE IN LOW LEVEL WIND SHEAR TONIGHT.

HIGH CONFIDENCE IN VFR CONDITIONS.

MEDIUM CONFIDENCE IN MAGNITUDE OF WIND GUSTS MONDAY.

BMD

//OUTLOOK FOR ORD/MDW FOR 06Z TUESDAY-12Z SUNDAY...UPDATED 18Z...

MONDAY NIGHT...SLIGHT CHANCE TSRA OTHERWISE VFR.
TUESDAY...VFR. WIND GUSTS TO 30 KTS POSSIBLE DURING THE DAY.
WEDNESDAY...VFR.
THURSDAY...SLIGHT CHANCE TSRA OTHERWISE VFR.
FRIDAY...CHANCE TSRA OTHERWISE VFR.
SATURDAY...CHANCE TSRA OTHERWISE VFR.

BMD

&&

.MARINE...
232 PM CDT

A TIGHT PRESSURE GRADIENT PERSISTS TODAY BETWEEN A RIDGE OF HIGH
PRESSURE THAT EXTENDS FROM THE EAST COAST INTO TENNESSEE AND A LOW
PRESSURE SYSTEM OVER THE CENTRAL PLAINS. A WARM FRONT LIFTING ACROSS
THE LAKE THIS EVENING WILL BRING A CHANCE OF SHOWERS AND
THUNDERSTORMS TONIGHT. AS THE COLD FRONT APPROACHES THE AREA
TOMORROW...THE PRESSURE GRADIENT WILL TIGHTEN AND WINDS ARE EXPECTED
TO INCREASE TO GALES BY LATE MONDAY NIGHT/TUESDAY MORNING AND LAST
THROUGH EARLY WEDNESDAY MORNING. WINDS WILL BE SOUTH TO SOUTHWEST
THROUGH THIS PERIOD BEFORE FINALLY COMING AROUND TO THE NORTHWEST
AND GRADUALLY DIMINISHING BEHIND THE COLD FRONT. HIGH PRESSURE THEN
WILL BUILD INTO THE UPPER MIDWEST WEDNESDAY AND BOTH WINDS AND WAVES
WILL SUBSIDE THROUGHOUT THE DAY.

BMD

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...GALE WATCH...LMZ080-LMZ567-LMZ669-LMZ671-LMZ673-LMZ675-LMZ777-
     LMZ779-LMZ868-LMZ870-LMZ872-LMZ874-LMZ876-LMZ878...MIDNIGHT
     TUESDAY TO 9 PM TUESDAY.

     GALE WATCH...LMZ261-LMZ362-LMZ364-LMZ366-LMZ563-LMZ565...5 AM
     TUESDAY TO 9 PM TUESDAY.

&&

$$

000
FXUS63 KILX 051736
AFDILX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LINCOLN IL
1236 PM CDT SUN SEP 5 2010

.DISCUSSION...
ISSUED 1026 AM CDT SUN SEP 5 2010

MORNING SURFACE ANALYSIS SHOWS HIGH PRESSURE CENTERED OVER EASTERN
KENTUCKY...WITH SOUTHERLY RETURN FLOW NOTED ACROSS CENTRAL ILLINOIS.
AREA OF MID-LEVEL CLOUDS HAS DEVELOPED IN ZONE OF STRONGEST WARM
ADVECTION FROM EASTERN NEBRASKA EASTWARD INTO NORTHERN ILLINOIS.
ISOLATED SHOWERS HAVE EVEN DEVELOPED ACROSS SOUTHWEST
IOWA/NORTHWEST MISSOURI...BUT THESE ARE EXPECTED TO DISSIPATE AS
THE TRACK FURTHER EAST INTO A RATHER DRY LOW-LEVEL AIRMASS ACROSS
ILLINOIS. GENERAL FORECAST OF MOSTLY SUNNY SKIES IS STILL ON
TRACK...WITH AFTERNOON HIGHS A FEW DEGREES WARMER THAN YESTERDAY
IN THE UPPER 70S. HAVE MADE SOME ADJUSTMENTS TO HOURLY
TEMPS/DEWPOINTS...BUT CHANGES ARE TOO MINOR TO WARRANT A ZONE
UPDATE AT THIS TIME.

&&

.AVIATION...
ISSUED 1236 PM CDT SUN SEP 5 2010

PATCHY MID CLOUDS CURRENTLY ACROSS IOWA AND NORTHERN MISSOURI WILL
DRIFT EASTWARD INTO CENTRAL ILLINOIS THIS AFTERNOON AND
EVENING...MAINLY IMPACTING THE WESTERN TERMINALS. BASED ON
FORECAST SOUNDINGS AND UPSTREAM OBS...CLOUD BASES WILL GENERALLY
REMAIN AOA 12000FT. AS MID-LEVEL WARM ADVECTION INCREASES THIS
EVENING...SOME OF THE MODELS ARE SUGGESTING A FEW SPRINKLES OR
LIGHT SHOWERS WILL DEVELOP ACROSS WEST-CENTRAL AND NORTHWEST
ILLINOIS. THINK THESE WILL BE ISOLATED IN NATURE IF THEY OCCUR AT
ALL...SO HAVE NOT INCLUDED VCSH AT ANY OF THE TAF SITES. GUSTY
S/SE WINDS THIS AFTERNOON WILL DIMINISH AFTER SUNSET...HOWEVER
LOW-LEVEL JET WILL INCREASE MARKEDLY. AS A RESULT...HAVE INCLUDED
WIND SHEAR ACROSS THE ENTIRE AREA...WITH 40KT AT 2000FT ACROSS THE
WESTERN SITES TAPERING DOWN TO 30KT AT KCMI. AS THIS WIND ENERGY
GETS MIXED DOWN MONDAY MORNING...SURFACE WINDS WILL GUST TO 20 TO
25KT...AND PERHAPS EVEN HIGHER BY AFTERNOON.

BARNES
&&

.PREV DISCUSSION...
ISSUED 330 AM CDT SUN SEP 5 2010

00Z MODELS REMAIN IN FAIR AGREEMENT NEXT FEW DAYS THEN DIVERGE
LATER IN THE WEEK. MODELS CONTINUE TO SHOW STRONG LOW PRESSURE
PASSING WELL NORTH OF IL MON NIGHT/TUE WITH WEAKENING FRONT MOVING
THROUGH CENTRAL/SE IL WITH BREEZY CONDITIONS AND LITTLE OR NO QPF
DUE TO VERY LIMITED MOISTURE. LEANED ON THE WARMER MAV HIGHS NEXT
FEW DAYS WHICH HAVE BETTER TRACK RECORD.

SHORT TERM...TODAY THROUGH TUESDAY NIGHT.

WEAK HIGH PRESSURE 1017 MB OVER THE OHIO AND MID MS VALLEYS
PROVIDING CLEAR SKIES AND CALM WINDS OVER CENTRAL/SE IL EARLY
THIS MORNING. COOL FALL LIKE TEMPS IN THE UPPER 40S AND LOWER 50S
AND COOLEST MORNING SINCE MAY 19TH.

ANOTHER NICE DAY AHEAD WITH PARTLY TO MOSTLY SUNNY SKIES AND
MILDER HIGHS IN THE UPPER 70S TO NEAR 80F. WEAK HIGH PRESSURE OVER
THE OHIO VALLEY TO DRIFT EAST INTO THE MID ATLANTIC STATES TONIGHT
WHILE LOW PRESSURE DEEPENS OVER NEBRASKA. STRONG UPPER LEVEL LOW
ALONG THE ALBERTA AND SASKATCHEWAN PROVINCE LINE DIGS INTO THE
NORTHERN PLAINS MON AND BRINGS DEEP LOW PRESSURE INTO THE UPPER MS
VALLEY. TIGHTENING PRESSURE GRADIENT OVER IL MON WITH INCREASING
SSW WINDS BRINGING WARMER AIR WITH HIGHS IN THE MID 80S CENTRAL IL
AND UPPER 80S SE IL.

MODELS HAVE TRENDED QUICKER WITH FRONT MOVING THROUGH IL OVERNIGHT
MON NIGHT AND TUE MORNING AND GENERALLY COMES THROUGH DRY WITH
LIMITED MOISTURE TO WORK WITH AND UPPER LEVEL DYNAMICS PASSING
WELL NORTH OF CENTRAL IL OVER THE UPPER GREAT LAKES. HAVE JUST
SLIGHT CHANCE AT BEST OVER THE IL RIVER VALLEY AFTER MIDNIGHT MON
NIGHT AND OVER REST OF AREA TUE. WITH FASTER MOVEMENT OF FRONT
COOLED HIGHS A BIT ON TUE WITH AROUND 80F OVER THE IL RIVER VALLEY
AND NEAR 90F AT LAWRENCEVILLE. STILL BREEZY TUE WITH STRONG LOW
PRESSURE PASSING JUST NORTH OF MI.

LONG TERM...WEDNESDAY THROUGH SATURDAY.

EXTENDED MODELS BUILD UPPER LEVEL RIDGE INTO THE MS VALLEY WED-FRI
WHICH SHOULD ALLOW TEMPS TO MODIFY AGAIN DURING THIS TIME FRAME
WITH MID TO UPPER 80S FRI/SAT AND LAWRENCEVILLE NEAR 90F.
MOISTURE FROM THE WESTERN GULF LIFTING NORTHWARD INTO THE OZARKS
WED AND POSSIBLY INTO CENTRAL/SOUTHERN IL THU. CONTINUED TO HAVE
20-30% CHANCES SW AREAS WED AND ACROSS AREA THU.

HUETTL

&&

.ILX WATCHES/WARNINGS/ADVISORIES...
NONE.
&&

$$

000
FXUS63 KLOT 051735
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
1235 PM CDT SUN SEP 5 2010

.DISCUSSION...
339 AM CDT

WHILE CHANCES OF ANY APPRECIABLE PRECIPITATION ARE RATHER LOW FOR
THE LOCAL AREA OVER THE NEXT SEVERAL DAYS...PATTERN WILL BE FAIRLY
ACTIVE IN TERMS OF A VIGOROUS STORM SYSTEM TRACKING JUST NORTH OF
THE AREA THAT WILL BRING SOME MODERATING TEMPERATURES FOR MONDAY
AHEAD OF THE COLD FRONT...AND SOME WINDY CONDITIONS FOR MONDAY AND
TUESDAY.

IN THE NEAR TERM...QUIET WEATHER CONTINUES FOR THE LOCAL AREA AND
THE MOST INTERESTING WEATHER FEATURE TO WATCH FOR TODAY WILL BE MID
LEVEL CLOUDS INCREASING ACROSS THE AREA. IR SATELLITE IMAGERY OVER
PAST 1 TO 2 HOURS BEGINNING TO SHOW BLOSSOMING MID LEVEL CLOUD FROM
SOUTHWEST MINNESOTA INTO SOUTHEAST IOWA AT NOSE OF STRONGER MID
LEVEL WARM ADVECTION. MODELS SEEM TO HAVE HANDLED THIS INCREASING
MID LEVEL RH FAIRLY WELL THIS MORNING...AND SHOULD GRADUALLY SEE THIS
EXPANDING MID DECK WORK ITS WAY INTO NORTHERN ILLINOIS LATER THIS
MORNING AND THIS AFTERNOON.

SOME UPPER FORCING TO INCREASE ACROSS THE AREA THIS AFTERNOON AS A
VORT MAX ACROSS EASTERN SOUTH DAKOTA/EASTERN NEBRASKA PROGRESSES
THOUGH THE UPPER RIDGE AND INTO NORTHERN ILLINOIS. AS THIS
OCCURS...ISENTROPIC UPGLIDE WILL RAMP UP...ESPECIALLY TOWARD
EVENING. ANALYSIS OF NAM/GFS 305K ISENTROPIC SURFACES STILL
INDICATING THIS STRONGEST UPGLIDE ACROSS APPROX NORTHERN ONE
THIRD OF THE FORECAST AREA. EVEN WITH THIS UPGLIDE...CONDENSATIONAL
PRESSURE DEFICITS ON THIS SURFACE STILL 100-150 MB...WITH THE
LOWER VALUES FURTHER TO NORTH FROM CENTRAL WISCONSIN INTO CENTRAL
LOWER MICHIGAN. PRECIPITATION PROB STILL LOOKING QUITE MEAGER
TODAY. EVEN THOUGH SOUTHERLY LOW LEVEL FLOW WILL RAMP UP LATER
THIS AFTERNOON...UPSTREAM MOISTURE PROFILES PER 00Z RAOBS FROM
LAST EVENING ARE NOTHING IMPRESSIVE WITH 850 HPA DEW PTS OF -2 DEG
CELSIUS AT KLZK AND +5 DEG CELSIUS AT KSGF. GIVEN STRENGTH OF
ISENTROPIC UPGLIDE...DID NOT WANT TO COMPLETELY REMOVE POPS FOR
TONIGHT...ALTHOUGH WITH SUCH DRY LOW LEVELS WILL TONE DOWN MENTION
TO SLIGHT CHANCE OF LIGHT RAIN SHOWERS OR SPRINKLES. EXPECTING
TEMPERATURES TODAY TO BE 5 TO 10 DEGREES WARMER THAN YESTERDAY AND
THE MAGNITUDE OF MODERATION TODAY WILL BE SOMEWHAT CONTROLLED BY
EXTENT AND TIMING OF MID LEVEL CLOUD INCREASE THIS AFTERNOON.

BY 12Z MONDAY...FOCUS FOR STRONGER ISENTROPIC LIFT WILL SHIFT
NORTHWARD INTO SOUTHERN/CENTRAL WISCONSIN WITH LOW LEVEL WARM FRONT...
SO HAVE MADE NO CHANGES TO A DRY MONDAY FORECAST AS SOME OF THAT
FAIRLY DRY LOW LEVEL AIR CURRENTLY ACROSS LOWER MS RIVER VALLEY
ADVECTS NORTHWARD. MAIN AXIS OF MOISTURE TRANSPORT MONDAY WILL
OCCUR TO THE WEST ACROSS THE CENTRAL AND NORTHERN PLAINS AS
THE VIGOROUS UPPER LEVEL TROUGH TRACKS EAST OUT OF THE ROCKIES.
WITH LOW LEVEL RIDGE ACROSS LOWER MS RVR VALLEY BEING SLOW TO
TRUDGE EASTWARD...IT STILL APPEARS AS THOUGH MORE SIGNIFICANT LOW
LEVEL MOISTURE WILL BE CONFINED TO NARROW FRONTAL AXIS ONCE AGAIN
AND ANY CHANCE OF PRECIP FOR LOCAL AREA WILL HOLD OFF UNTIL MONDAY
NIGHT AS FRONT APPROACHES. OTHERWISE...MONDAY LOOKING TO BE QUITE
WARM WITH ABOVE NORMAL HIGHS REACHING INTO THE LOWER TO MID 80S
FOR THE AREA WITH SOUTH GUSTS OF 30 TO 35 MPH POSSIBLE IN THE
AFTERNOON. MODELS ARE IN GENERAL AGREEMENT IN OCCLUDING SYSTEM
MONDAY NIGHT INTO EARLY TUESDAY WITH INITIALLY BETTER UPPER
DYNAMICS/LOW LEVEL CONVG MONDAY AFTERNOON/EARLY EVENING SETTING UP
ACROSS PORTIONS OF IOWA/SOUTHERN MINNESOTA. AT THIS TIME...STILL
FEEL BETTER CONVECTIVE CHANCES WILL BE GENERALLY WEST OF MS
RIVER...ALTHOUGH WILL MAINTAIN SLIGHT CHANCE POPS FOR THUNDER FROM
WEST TO EAST MONDAY NIGHT.

SYSTEM WILL SLOWLY FILL TUESDAY AS DRY LOW/MID LEVEL AIR WORKS
INTO THE AREA. THERE MAY BE SOME ISOLD SHOWERS ALONG THE FRONT
EARLY TUESDAY ACROSS SOUTHEASTERN PORTIONS OF THE AREA...BUT
OVERWHELMING DRY AIR ADVECTION ACROSS THE AREA SHOULD RESULT IN
DRY AND VERY WINDY CONDITIONS FOR TUES AFTERNOON. COLD ADVECTION
TUESDAY AFTERNOON WILL ALLOW FOR MORE SUBSTANTIAL MIXED LAYER
DEPTHS AND EVEN SOME CONCERN FOR NUDGING UP AGAINST WIND ADVISORY
CRITERIA AND WILL INCLUDE MENTION OF THESE EXPECTED VERY WINDY
CONDITIONS IN THIS MORNINGS HWO. TEMPS RATHER TRICKY ON TUESDAY
WITH COLD ADVECTION FIGHTING THE EFFECTS OF DEEPER MIXING. MAY BE
A BIT WARM WITH HIGHS TUESDAY RANGING FROM MID 70S FAR NORTH
CENTRAL ILLINOIS TO LOWER 80S FAR SOUTHEAST...BUT THIS DOES APPEAR
TO BE A COMMON SETUP WHEN THE EFFECTS OF SUBSIDENCE/MIXING DO
ALLOW FOR WARMER THAN EXPECTED TEMPS...SO HAVE NOT CHANGED THESE
HIGHS MUCH AT THIS POINT WITH STILL SOME SUBTLE MODEL DIFFERENCES
IN TIMING THIS COLD ADVECTION.

WEATHER TO FINALLY QUIET DOWN TUESDAY NIGHT INTO WEDNESDAY AS NEXT
SFC HIGH SLIDES INTO THE REGION. LOW LEVEL FRONT NOT EXPECTED TO BE
TOO FAR SOUTH OF THE AREA...ALTHOUGH NOT EXPECTING THIS LOW LEVEL
BAROCLINIC ZONE TO BE ACTIVE WITH ANY PRECIP DUE TO LIMITED
MOISTURE. NEW MEDIUM RANGE MODELS STILL SUPPORT THE GOING EXTENDED
FORECAST OF CHANCES OF THUNDER LATE THURSDAY/FRIDAY WITH RENEWED
THETA-E ADVECTION IN ADVANCE OF NEXT SIGNIFICANT UPPER TROUGH
WORKING THROUGH NWRN CONUS. THIS PATTERN SHOULD ALSO ALLOW MUCH OF
THE AREA TO POTENTIALLY WARM BACK INTO THE LOWER 80S TOWARD THE END
OF THE WEEK.

MARSILI

&&

.FIRE WEATHER...
330 AM CDT

SFC PRESSURE GRADIENT WILL STRENGTHEN ON MONDAY AS STRONG SFC LOW
MOVES INTO SOUTHERN MINNESOTA. STILL SOME UNCERTAINTY REMAINS AS
TO MIXING HEIGHTS MONDAY AFTERNOON AND EXACTLY HOW MUCH LOW LEVEL
DRY AIR CAN MIX DOWN TO THE SURFACE. FORECASTED HIGHS INTO THE
LOWER TO MID 80S COMBINED WITH DEW PTS LIKELY MIXING OUT TO AROUND
50 WOULD SUPPORT MIN AFTERNOON RELATIVE HUMIDITIES AROUND 30
PERCENT. WHILE WIND GUSTS SHOULD BE UP AROUND 30 MPH MONDAY
AFTERNOON...ENOUGH UNCERTAINTY EXISTS WITH REGARDS TO MIXING AND
FUEL MOISTURES TO HOLD OFF ON ANY FIRE WEATHER HEADLINES AT THIS
TIME.

TUESDAY IS SHAPING UP AS ANOTHER DAY OF POTENTIAL FIRE WEATHER
CONCERN AS CONFIDENCE IN DEEPER MIXED LAYER IS HIGHER ALONG WITH
POTENTIAL OF SOME SOUTHWEST WIND GUSTS TO 40 TO 45 MPH. IN
CONTRAST TO MONDAY THE MAIN ELEMENT OF UNCERTAINTY WITH HOW LOW
AFTERNOON RELATIVE HUMIDITIES CAN REACH IS JUST HOW HIGH THE
TEMPERATURE WILL CLIMB. AT THIS TIME...HAVE FORECASTED MIN
AFTERNOON RELATIVE HUMIDITIES IN THE 30 TO 35 PERCENT RANGE BUT
THIS WILL NEED TO BE MONITORED FOR ANY CHANGES TO FUTURE
FORECASTS. ALSO IF FRONTAL PASSAGE DOES COME THROUGH DRY MONDAY
NIGHT INTO TUESDAY...FUEL MOISTURES WILL BE SOMEWHAT LOWER WHICH
WOULD INCREASE FIRE WEATHER RISK FOR TUESDAY.

MARSILI

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 18Z...

WINDS A LITTLE STRONGER THAN ORIGINALLY ANTICIPATED. BUMPED UP WINDS
ACROSS THE BOARD ADDING GUSTS FOR THIS AFTERNOON. TERMINAL WINDS
VARYING BETWEEN 190-260.

WIND SHEAR CONDITIONS EXPECTED TONIGHT AND STRONG GUSTS ARE
ANTICIPATED ON MONDAY.

BMD

//DISCUSSION...UPDATED 18Z...

PRESSURE GRADIENT TIGHTENING OVER THE NEXT 24HRS BETWEEN A RIDGE OF
HIGH PRESSURE OVER THE OHIO RIVER VALLEY AND A DEVELOPING LOW
PRESSURE SYSTEM OVER THE CENTRAL PLAINS. WINDS ARE GRADUALLY
EXPECTED TO BACK TO A MORE SOUTHERLY DIRECTION AND INCREASE IN
MAGNITUDE AS THE PATTERN SHIFTS EAST TODAY. A WEAK WARM FRONT
LIFTING THROUGH THE AREA IS BRINGING A MID LEVEL CLOUD DECK BUT
CONDITIONS SHOULD REMAIN DRY EXPECT FOR AN ISOLATED SPRINKLE OR
SHOWER. AS ATMOSPHERE DECOUPLES LATE TONIGHT...EXPECT LOW LEVEL WIND
SHEAR. STRONG WINDS WILL BE UNABLE TO MIX TO THE SURFACE AND WINDS
AT 2K FT AROUND 40-45KTS ARE EXPECTED WITH UPWARDS OF 50KTS BRIEFLY
POSSIBLE.

MONDAY WILL BE VERY WINDY AGAIN AS COLD FRONT APPROACHES FROM THE
WEST. MAGNITUDE OF WIND GUSTS ARE EXPECTED TO INCREASE THROUGH THE
DAY AS THE DEPTH OF THE MIXED LAYER INCREASES. GUSTS TO AROUND 40KTS
MAY BE POSSIBLE JUST BEYOND THE CURRENT TAF PERIOD.

BMD

//ORD AND MDW CONFIDENCE...UPDATED 18Z...

HIGH CONFIDENCE IN LOW LEVEL WIND SHEAR TONIGHT.

HIGH CONFIDENCE IN VFR CONDITIONS.

MEDIUM CONFIDENCE IN MAGNITUDE OF WIND GUSTS MONDAY.

BMD

//OUTLOOK FOR ORD/MDW FOR 06Z TUESDAY-12Z SUNDAY...UPDATED 18Z...

MONDAY NIGHT...SLIGHT CHANCE TSRA OTHERWISE VFR.
TUESDAY...VFR. WIND GUSTS TO 30 KTS POSSIBLE DURING THE DAY.
WEDNESDAY...VFR.
THURSDAY...SLIGHT CHANCE TSRA OTHERWISE VFR.
FRIDAY...CHANCE TSRA OTHERWISE VFR.
SATURDAY...CHANCE TSRA OTHERWISE VFR.

BMD

&&

.MARINE...
330 AM CDT

STILL SEEING SOME ACCELERATION OF THE WINDS THIS MORNING OVER
EASTERN PORTIONS OF THE LAKE NEAR THE LAKE INSTABILITY INDUCED
CONVERGENCE BANDS. THOSE LOCALIZED WIND MAXIMA WILL FADE AFTER
SUNRISE WITH GRADIENT RELAXING AND WINDS BACKING IN ADVANCE OF THE
NEXT STORM SYSTEM.

MODEL GUIDANCE REMAINS IN EXCELLENT AGREEMENT ON TRACKING A DEEP LOW
FROM THE HIGH PLAINS THIS EVENING TO LAKE SUPERIOR BY TUESDAY
MORNING. VERY STRONG PRESSURE GRADIENT ASSOCIATED WITH THIS LARGE
AND RATHER INTENSE LOW SHOULD RESULT IN AN EXTENDED PERIOD OF HIGH
WINDS/WAVES. FORECAST SOUNDINGS FROM THE GFS/WRF-NAM BOTH CONTINUE
TO SUGGEST SUFFICIENTLY STEEP LOW LEVEL LAPSE RATES MONDAY INTO
MONDAY EVENING TO TAP INTO THE GALE FORCE WINDS ALOFT...HOWEVER
STRONGLY SUSPECT THAT WATER TEMPS IN THE MODELS ARE TOO WARM AND DO
NOT ACCOUNT FOR THE RECENT UPWELLING THAT HAS OCCURRED. MODEL 2M
TEMPS ARE PROGGED TO GET INTO THE MID-UPPER 70S OVER THE LAKE AND
INTO THE 80S OVER LAND...WHICH BEING ADVECTED OVER TOP THE UPPER
60/NEAR 70F WATERS SHOULD RESULT IN A NOTICEABLY MORE STABLE MARINE
LAYER MONDAY INTO MONDAY EVENING. FOR THIS REASON HAVE UNDERCUT
MODEL WINDS AND PARTICULARLY GUSTS AND HELD SPEEDS JUST BELOW GALE
FORCE THRU MON EVENING.

LATER MONDAY NIGHT INTO TUESDAY AS OCCLUDED FRONT MOVE THROUGH
EXPECT COLD AIR ADVECTION TO STEEPEN UP THE LAPSE RATES AND ALLOW
WINDS TO REALLY RAMP UP OVER THE LAKE. WHILE LOW WILL BE IN A
WEAKENING PHASE TUESDAY...THAT WILL ACTUALLY ONLY WORK TO ENHANCE
THE PRESSURE RISES AS THE LOW PULLS OFF TO THE EAST. GIVEN
THIS...HAVE FOLLOWED MODEL GUIDANCE WHICH IS IN GOOD AGREEMENT ON
GALES DEVELOPING LATE MONDAY NIGHT AND LASTING UNTIL TUESDAY
EVENING. GIVEN THE STRONG MODEL CONSENSUS AND RUN-TO-RUN CONSISTENCY
HAVE GONE AHEAD AND HOISTED A GALE WATCH FOR THE OPEN LAKE FOR LATE
MON NIGHT INTO TUESDAY. GALE WATCH MAY WELL NEED TO BE EXPANDED INTO
THE NEARSHORE WATERS AS WELL...BUT THAT WILL BE A 5TH PERIOD EVENT
AND WITH SLIGHTLY LESSER CONFIDENCE THAN OVER THE OPEN LAKE WILL
PUNT THAT DECISION TO THE LATER SHIFTS.

IZZI

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...GALE WATCH...LMZ080-LMZ567-LMZ669-LMZ671-LMZ673-LMZ675-LMZ777-
     LMZ779-LMZ868-LMZ870-LMZ872-LMZ874-LMZ876-LMZ878...MIDNIGHT
     TUESDAY TO 9 PM TUESDAY.

     GALE WATCH...LMZ261-LMZ362-LMZ364-LMZ366-LMZ563-LMZ565...5 AM
     TUESDAY TO 9 PM TUESDAY.

&&

$$

000
FXUS63 KILX 051526
AFDILX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LINCOLN IL
1026 AM CDT SUN SEP 5 2010

.DISCUSSION...
ISSUED 1026 AM CDT SUN SEP 5 2010

MORNING SURFACE ANALYSIS SHOWS HIGH PRESSURE CENTERED OVER EASTERN
KENTUCKY...WITH SOUTHERLY RETURN FLOW NOTED ACROSS CENTRAL ILLINOIS.
AREA OF MID-LEVEL CLOUDS HAS DEVELOPED IN ZONE OF STRONGEST WARM
ADVECTION FROM EASTERN NEBRASKA EASTWARD INTO NORTHERN ILLINOIS.
ISOLATED SHOWERS HAVE EVEN DEVELOPED ACROSS SOUTHWEST
IOWA/NORTHWEST MISSOURI...BUT THESE ARE EXPECTED TO DISSIPATE AS
THE TRACK FURTHER EAST INTO A RATHER DRY LOW-LEVEL AIRMASS ACROSS
ILLINOIS. GENERAL FORECAST OF MOSTLY SUNNY SKIES IS STILL ON
TRACK...WITH AFTERNOON HIGHS A FEW DEGREES WARMER THAN YESTERDAY
IN THE UPPER 70S. HAVE MADE SOME ADJUSTMENTS TO HOURLY
TEMPS/DEWPOINTS...BUT CHANGES ARE TOO MINOR TO WARRANT A ZONE
UPDATE AT THIS TIME.

BARNES
&&

.AVIATION...
ISSUED 648 AM CDT SUN SEP 5 2010

MAINLY QUIET/VFR AVIATION WEATHER CONDITIONS EXPECTED THROUGH THE
12Z TAF VALID TIME. A RIDGE OF HIGH PRESSURE HAS SHIFTED JUST EAST
OF THE CENTRAL ILLINOIS TERMINALS...WITH SOUTHERLY WINDS
ANTICIPATED ON ITS BACK SIDE TODAY. SOME GUSTS ARE POSSIBLE DURING
PEAK DIURNAL HEATING...BUT THEY SHOULD GENERALLY BE AOB 20 KTS.
LLWS IS EXPECTED TO DEVELOP TONIGHT AS SURFACE WINDS DECOUPLE AND A
LOW LEVEL JET DEVELOPS JUST OFF THE SURFACE. OTHERWISE...CLOUD
COVER SHOULD BE MINIMAL INITIALLY...WITH HIGH BASED VFR CIGS
DEVELOPING TONIGHT IN ADVANCE OF A DEVELOPING FRONTAL SYSTEM IN
THE PLAINS.

BAK
&&

.PREV DISCUSSION...
ISSUED 330 AM CDT SUN SEP 5 2010

00Z MODELS REMAIN IN FAIR AGREEMENT NEXT FEW DAYS THEN DIVERGE
LATER IN THE WEEK. MODELS CONTINUE TO SHOW STRONG LOW PRESSURE
PASSING WELL NORTH OF IL MON NIGHT/TUE WITH WEAKENING FRONT MOVING
THROUGH CENTRAL/SE IL WITH BREEZY CONDITIONS AND LITTLE OR NO QPF
DUE TO VERY LIMITED MOISTURE. LEANED ON THE WARMER MAV HIGHS NEXT
FEW DAYS WHICH HAVE BETTER TRACK RECORD.

SHORT TERM...TODAY THROUGH TUESDAY NIGHT.

WEAK HIGH PRESSURE 1017 MB OVER THE OHIO AND MID MS VALLEYS
PROVIDING CLEAR SKIES AND CALM WINDS OVER CENTRAL/SE IL EARLY
THIS MORNING. COOL FALL LIKE TEMPS IN THE UPPER 40S AND LOWER 50S
AND COOLEST MORNING SINCE MAY 19TH.

ANOTHER NICE DAY AHEAD WITH PARTLY TO MOSTLY SUNNY SKIES AND
MILDER HIGHS IN THE UPPER 70S TO NEAR 80F. WEAK HIGH PRESSURE OVER
THE OHIO VALLEY TO DRIFT EAST INTO THE MID ATLANTIC STATES TONIGHT
WHILE LOW PRESSURE DEEPENS OVER NEBRASKA. STRONG UPPER LEVEL LOW
ALONG THE ALBERTA AND SASKATCHEWAN PROVINCE LINE DIGS INTO THE
NORTHERN PLAINS MON AND BRINGS DEEP LOW PRESSURE INTO THE UPPER MS
VALLEY. TIGHTENING PRESSURE GRADIENT OVER IL MON WITH INCREASING
SSW WINDS BRINGING WARMER AIR WITH HIGHS IN THE MID 80S CENTRAL IL
AND UPPER 80S SE IL.

MODELS HAVE TRENDED QUICKER WITH FRONT MOVING THROUGH IL OVERNIGHT
MON NIGHT AND TUE MORNING AND GENERALLY COMES THROUGH DRY WITH
LIMITED MOISTURE TO WORK WITH AND UPPER LEVEL DYNAMICS PASSING
WELL NORTH OF CENTRAL IL OVER THE UPPER GREAT LAKES. HAVE JUST
SLIGHT CHANCE AT BEST OVER THE IL RIVER VALLEY AFTER MIDNIGHT MON
NIGHT AND OVER REST OF AREA TUE. WITH FASTER MOVEMENT OF FRONT
COOLED HIGHS A BIT ON TUE WITH AROUND 80F OVER THE IL RIVER VALLEY
AND NEAR 90F AT LAWRENCEVILLE. STILL BREEZY TUE WITH STRONG LOW
PRESSURE PASSING JUST NORTH OF MI.

LONG TERM...WEDNESDAY THROUGH SATURDAY.

EXTENDED MODELS BUILD UPPER LEVEL RIDGE INTO THE MS VALLEY WED-FRI
WHICH SHOULD ALLOW TEMPS TO MODIFY AGAIN DURING THIS TIME FRAME
WITH MID TO UPPER 80S FRI/SAT AND LAWRENCEVILLE NEAR 90F.
MOISTURE FROM THE WESTERN GULF LIFTING NORTHWARD INTO THE OZARKS
WED AND POSSIBLY INTO CENTRAL/SOUTHERN IL THU. CONTINUED TO HAVE
20-30% CHANCES SW AREAS WED AND ACROSS AREA THU.

HUETTL

&&

.ILX WATCHES/WARNINGS/ADVISORIES...
NONE.
&&

$$

000
FXUS63 KLOT 051509
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
1009 AM CDT SUN SEP 5 2010

.DISCUSSION...
339 AM CDT

WHILE CHANCES OF ANY APPRECIABLE PRECIPITATION ARE RATHER LOW FOR
THE LOCAL AREA OVER THE NEXT SEVERAL DAYS...PATTERN WILL BE FAIRLY
ACTIVE IN TERMS OF A VIGOROUS STORM SYSTEM TRACKING JUST NORTH OF
THE AREA THAT WILL BRING SOME MODERATING TEMPERATURES FOR MONDAY
AHEAD OF THE COLD FRONT...AND SOME WINDY CONDITIONS FOR MONDAY AND
TUESDAY.

IN THE NEAR TERM...QUIET WEATHER CONTINUES FOR THE LOCAL AREA AND
THE MOST INTERESTING WEATHER FEATURE TO WATCH FOR TODAY WILL BE MID
LEVEL CLOUDS INCREASING ACROSS THE AREA. IR SATELLITE IMAGERY OVER
PAST 1 TO 2 HOURS BEGINNING TO SHOW BLOSSOMING MID LEVEL CLOUD FROM
SOUTHWEST MINNESOTA INTO SOUTHEAST IOWA AT NOSE OF STRONGER MID
LEVEL WARM ADVECTION. MODELS SEEM TO HAVE HANDLED THIS INCREASING
MID LEVEL RH FAIRLY WELL THIS MORNING...AND SHOULD GRADUALLY SEE THIS
EXPANDING MID DECK WORK ITS WAY INTO NORTHERN ILLINOIS LATER THIS
MORNING AND THIS AFTERNOON.

SOME UPPER FORCING TO INCREASE ACROSS THE AREA THIS AFTERNOON AS A
VORT MAX ACROSS EASTERN SOUTH DAKOTA/EASTERN NEBRASKA PROGRESSES
THOUGH THE UPPER RIDGE AND INTO NORTHERN ILLINOIS. AS THIS
OCCURS...ISENTROPIC UPGLIDE WILL RAMP UP...ESPECIALLY TOWARD
EVENING. ANALYSIS OF NAM/GFS 305K ISENTROPIC SURFACES STILL
INDICATING THIS STRONGEST UPGLIDE ACROSS APPROX NORTHERN ONE
THIRD OF THE FORECAST AREA. EVEN WITH THIS UPGLIDE...CONDENSATIONAL
PRESSURE DEFICITS ON THIS SURFACE STILL 100-150 MB...WITH THE
LOWER VALUES FURTHER TO NORTH FROM CENTRAL WISCONSIN INTO CENTRAL
LOWER MICHIGAN. PRECIPITATION PROB STILL LOOKING QUITE MEAGER
TODAY. EVEN THOUGH SOUTHERLY LOW LEVEL FLOW WILL RAMP UP LATER
THIS AFTERNOON...UPSTREAM MOISTURE PROFILES PER 00Z RAOBS FROM
LAST EVENING ARE NOTHING IMPRESSIVE WITH 850 HPA DEW PTS OF -2 DEG
CELSIUS AT KLZK AND +5 DEG CELSIUS AT KSGF. GIVEN STRENGTH OF
ISENTROPIC UPGLIDE...DID NOT WANT TO COMPLETELY REMOVE POPS FOR
TONIGHT...ALTHOUGH WITH SUCH DRY LOW LEVELS WILL TONE DOWN MENTION
TO SLIGHT CHANCE OF LIGHT RAIN SHOWERS OR SPRINKLES. EXPECTING
TEMPERATURES TODAY TO BE 5 TO 10 DEGREES WARMER THAN YESTERDAY AND
THE MAGNITUDE OF MODERATION TODAY WILL BE SOMEWHAT CONTROLLED BY
EXTENT AND TIMING OF MID LEVEL CLOUD INCREASE THIS AFTERNOON.

BY 12Z MONDAY...FOCUS FOR STRONGER ISENTROPIC LIFT WILL SHIFT
NORTHWARD INTO SOUTHERN/CENTRAL WISCONSIN WITH LOW LEVEL WARM FRONT...
SO HAVE MADE NO CHANGES TO A DRY MONDAY FORECAST AS SOME OF THAT
FAIRLY DRY LOW LEVEL AIR CURRENTLY ACROSS LOWER MS RIVER VALLEY
ADVECTS NORTHWARD. MAIN AXIS OF MOISTURE TRANSPORT MONDAY WILL
OCCUR TO THE WEST ACROSS THE CENTRAL AND NORTHERN PLAINS AS
THE VIGOROUS UPPER LEVEL TROUGH TRACKS EAST OUT OF THE ROCKIES.
WITH LOW LEVEL RIDGE ACROSS LOWER MS RVR VALLEY BEING SLOW TO
TRUDGE EASTWARD...IT STILL APPEARS AS THOUGH MORE SIGNIFICANT LOW
LEVEL MOISTURE WILL BE CONFINED TO NARROW FRONTAL AXIS ONCE AGAIN
AND ANY CHANCE OF PRECIP FOR LOCAL AREA WILL HOLD OFF UNTIL MONDAY
NIGHT AS FRONT APPROACHES. OTHERWISE...MONDAY LOOKING TO BE QUITE
WARM WITH ABOVE NORMAL HIGHS REACHING INTO THE LOWER TO MID 80S
FOR THE AREA WITH SOUTH GUSTS OF 30 TO 35 MPH POSSIBLE IN THE
AFTERNOON. MODELS ARE IN GENERAL AGREEMENT IN OCCLUDING SYSTEM
MONDAY NIGHT INTO EARLY TUESDAY WITH INITIALLY BETTER UPPER
DYNAMICS/LOW LEVEL CONVG MONDAY AFTERNOON/EARLY EVENING SETTING UP
ACROSS PORTIONS OF IOWA/SOUTHERN MINNESOTA. AT THIS TIME...STILL
FEEL BETTER CONVECTIVE CHANCES WILL BE GENERALLY WEST OF MS
RIVER...ALTHOUGH WILL MAINTAIN SLIGHT CHANCE POPS FOR THUNDER FROM
WEST TO EAST MONDAY NIGHT.

SYSTEM WILL SLOWLY FILL TUESDAY AS DRY LOW/MID LEVEL AIR WORKS
INTO THE AREA. THERE MAY BE SOME ISOLD SHOWERS ALONG THE FRONT
EARLY TUESDAY ACROSS SOUTHEASTERN PORTIONS OF THE AREA...BUT
OVERWHELMING DRY AIR ADVECTION ACROSS THE AREA SHOULD RESULT IN
DRY AND VERY WINDY CONDITIONS FOR TUES AFTERNOON. COLD ADVECTION
TUESDAY AFTERNOON WILL ALLOW FOR MORE SUBSTANTIAL MIXED LAYER
DEPTHS AND EVEN SOME CONCERN FOR NUDGING UP AGAINST WIND ADVISORY
CRITERIA AND WILL INCLUDE MENTION OF THESE EXPECTED VERY WINDY
CONDITIONS IN THIS MORNINGS HWO. TEMPS RATHER TRICKY ON TUESDAY
WITH COLD ADVECTION FIGHTING THE EFFECTS OF DEEPER MIXING. MAY BE
A BIT WARM WITH HIGHS TUESDAY RANGING FROM MID 70S FAR NORTH
CENTRAL ILLINOIS TO LOWER 80S FAR SOUTHEAST...BUT THIS DOES APPEAR
TO BE A COMMON SETUP WHEN THE EFFECTS OF SUBSIDENCE/MIXING DO
ALLOW FOR WARMER THAN EXPECTED TEMPS...SO HAVE NOT CHANGED THESE
HIGHS MUCH AT THIS POINT WITH STILL SOME SUBTLE MODEL DIFFERENCES
IN TIMING THIS COLD ADVECTION.

WEATHER TO FINALLY QUIET DOWN TUESDAY NIGHT INTO WEDNESDAY AS NEXT
SFC HIGH SLIDES INTO THE REGION. LOW LEVEL FRONT NOT EXPECTED TO BE
TOO FAR SOUTH OF THE AREA...ALTHOUGH NOT EXPECTING THIS LOW LEVEL
BAROCLINIC ZONE TO BE ACTIVE WITH ANY PRECIP DUE TO LIMITED
MOISTURE. NEW MEDIUM RANGE MODELS STILL SUPPORT THE GOING EXTENDED
FORECAST OF CHANCES OF THUNDER LATE THURSDAY/FRIDAY WITH RENEWED
THETA-E ADVECTION IN ADVANCE OF NEXT SIGNIFICANT UPPER TROUGH
WORKING THROUGH NWRN CONUS. THIS PATTERN SHOULD ALSO ALLOW MUCH OF
THE AREA TO POTENTIALLY WARM BACK INTO THE LOWER 80S TOWARD THE END
OF THE WEEK.

MARSILI

&&

.FIRE WEATHER...
330 AM CDT

SFC PRESSURE GRADIENT WILL STRENGTHEN ON MONDAY AS STRONG SFC LOW
MOVES INTO SOUTHERN MINNESOTA. STILL SOME UNCERTAINTY REMAINS AS
TO MIXING HEIGHTS MONDAY AFTERNOON AND EXACTLY HOW MUCH LOW LEVEL
DRY AIR CAN MIX DOWN TO THE SURFACE. FORECASTED HIGHS INTO THE
LOWER TO MID 80S COMBINED WITH DEW PTS LIKELY MIXING OUT TO AROUND
50 WOULD SUPPORT MIN AFTERNOON RELATIVE HUMIDITIES AROUND 30
PERCENT. WHILE WIND GUSTS SHOULD BE UP AROUND 30 MPH MONDAY
AFTERNOON...ENOUGH UNCERTAINTY EXISTS WITH REGARDS TO MIXING AND
FUEL MOISTURES TO HOLD OFF ON ANY FIRE WEATHER HEADLINES AT THIS
TIME.

TUESDAY IS SHAPING UP AS ANOTHER DAY OF POTENTIAL FIRE WEATHER
CONCERN AS CONFIDENCE IN DEEPER MIXED LAYER IS HIGHER ALONG WITH
POTENTIAL OF SOME SOUTHWEST WIND GUSTS TO 40 TO 45 MPH. IN
CONTRAST TO MONDAY THE MAIN ELEMENT OF UNCERTAINTY WITH HOW LOW
AFTERNOON RELATIVE HUMIDITIES CAN REACH IS JUST HOW HIGH THE
TEMPERATURE WILL CLIMB. AT THIS TIME...HAVE FORECASTED MIN
AFTERNOON RELATIVE HUMIDITIES IN THE 30 TO 35 PERCENT RANGE BUT
THIS WILL NEED TO BE MONITORED FOR ANY CHANGES TO FUTURE
FORECASTS. ALSO IF FRONTAL PASSAGE DOES COME THROUGH DRY MONDAY
NIGHT INTO TUESDAY...FUEL MOISTURES WILL BE SOMEWHAT LOWER WHICH
WOULD INCREASE FIRE WEATHER RISK FOR TUESDAY.

MARSILI

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 15Z...

LOW LEVEL WIND SHEAR POSSIBLE TONIGHT.

BMD

//DISCUSSION...UPDATED 12Z...

SFC RIDGE AXIS OVERHEAD EARLY THIS MORNING WILL SHIFT OFF TO THE
EAST AND PROVIDE SOUTHERLY WINDS AROUND 10 KNOTS BY MID TO LATE
MORNING. SATELLITE IMAGERY EARLY THIS MORNING INDICATES EXPANDING
MID LEVEL CLOUDINESS DUE TO WARM ADVECTION...AND THESE MID LEVEL
CLOUDS SHOULD CONTINUE TO WORK EASTWARD THIS MORNING INTO NORTHERN
ILLINOIS. BY LATE TONIGHT...WARM ADVECTION UNDER THIS STRONG
SOUTHERLY LOW LEVEL JET AND BOUNDARY LAYER DECOUPLING WILL ALLOW
FOR THE POSSIBILITY OF LOW LEVEL WIND SHEAR AND HAVE NOT MADE ANY
SIGNIFICANT CHANGES FROM PREVIOUS TAF IN THIS REGARD. THREAT OF
LOW LEVEL WIND SHEAR WILL DIMINISH IN THE 13Z-15Z MONDAY TIMEFRAME
AS MIXING COMMENCES...WITH SOME GUSTS INTO THE 20 TO 25 KT RANGE
POSSIBLE BY MID TO LATE MORNING MONDAY. WILL CONTINUE TO KEEP
TAFS DRY TONIGHT AS ANY MOISTURE INCREASES WILL BE MORE MID LEVEL IN
NATURE MAKING IT HARD TO REALIZE ANY KIND OF SIGNIFICANT
INSTABILITY.

MARSILI

//ORD AND MDW CONFIDENCE...UPDATED 15Z...

HIGH CONFIDENCE IN VFR CONDITIONS.

MEDIUM CONFIDENCE IN LLWS CONDITIONS TONIGHT.

BMD

//OUTLOOK FOR ORD/MDW FOR 18Z MONDAY-12Z FRIDAY...UPDATED 06Z...

MONDAY...VFR. SOUTH WIND GUSTS OVER 30KT POSSIBLE DURING DAYTIME.
TUESDAY...VFR. SOUTHWEST->WEST WIND GUSTS OVER 30KT DURING DAYTIME.
WEDNESDAY...VFR.
THURSDAY AND FRIDAY...SLIGHT CHANCE OF TSRA OTHERWISE VFR.

IZZI

&&

.MARINE...
330 AM CDT

STILL SEEING SOME ACCELERATION OF THE WINDS THIS MORNING OVER
EASTERN PORTIONS OF THE LAKE NEAR THE LAKE INSTABILITY INDUCED
CONVERGENCE BANDS. THOSE LOCALIZED WIND MAXIMA WILL FADE AFTER
SUNRISE WITH GRADIENT RELAXING AND WINDS BACKING IN ADVANCE OF THE
NEXT STORM SYSTEM.

MODEL GUIDANCE REMAINS IN EXCELLENT AGREEMENT ON TRACKING A DEEP LOW
FROM THE HIGH PLAINS THIS EVENING TO LAKE SUPERIOR BY TUESDAY
MORNING. VERY STRONG PRESSURE GRADIENT ASSOCIATED WITH THIS LARGE
AND RATHER INTENSE LOW SHOULD RESULT IN AN EXTENDED PERIOD OF HIGH
WINDS/WAVES. FORECAST SOUNDINGS FROM THE GFS/WRF-NAM BOTH CONTINUE
TO SUGGEST SUFFICIENTLY STEEP LOW LEVEL LAPSE RATES MONDAY INTO
MONDAY EVENING TO TAP INTO THE GALE FORCE WINDS ALOFT...HOWEVER
STRONGLY SUSPECT THAT WATER TEMPS IN THE MODELS ARE TOO WARM AND DO
NOT ACCOUNT FOR THE RECENT UPWELLING THAT HAS OCCURRED. MODEL 2M
TEMPS ARE PROGGED TO GET INTO THE MID-UPPER 70S OVER THE LAKE AND
INTO THE 80S OVER LAND...WHICH BEING ADVECTED OVER TOP THE UPPER
60/NEAR 70F WATERS SHOULD RESULT IN A NOTICEABLY MORE STABLE MARINE
LAYER MONDAY INTO MONDAY EVENING. FOR THIS REASON HAVE UNDERCUT
MODEL WINDS AND PARTICULARLY GUSTS AND HELD SPEEDS JUST BELOW GALE
FORCE THRU MON EVENING.

LATER MONDAY NIGHT INTO TUESDAY AS OCCLUDED FRONT MOVE THROUGH
EXPECT COLD AIR ADVECTION TO STEEPEN UP THE LAPSE RATES AND ALLOW
WINDS TO REALLY RAMP UP OVER THE LAKE. WHILE LOW WILL BE IN A
WEAKENING PHASE TUESDAY...THAT WILL ACTUALLY ONLY WORK TO ENHANCE
THE PRESSURE RISES AS THE LOW PULLS OFF TO THE EAST. GIVEN
THIS...HAVE FOLLOWED MODEL GUIDANCE WHICH IS IN GOOD AGREEMENT ON
GALES DEVELOPING LATE MONDAY NIGHT AND LASTING UNTIL TUESDAY
EVENING. GIVEN THE STRONG MODEL CONSENSUS AND RUN-TO-RUN CONSISTENCY
HAVE GONE AHEAD AND HOISTED A GALE WATCH FOR THE OPEN LAKE FOR LATE
MON NIGHT INTO TUESDAY. GALE WATCH MAY WELL NEED TO BE EXPANDED INTO
THE NEARSHORE WATERS AS WELL...BUT THAT WILL BE A 5TH PERIOD EVENT
AND WITH SLIGHTLY LESSER CONFIDENCE THAN OVER THE OPEN LAKE WILL
PUNT THAT DECISION TO THE LATER SHIFTS.

IZZI

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...GALE WATCH...LMZ080-LMZ567-LMZ669-LMZ671-LMZ673-LMZ675-LMZ777-
     LMZ779-LMZ868-LMZ870-LMZ872-LMZ874-LMZ876-LMZ878...MIDNIGHT
     TUESDAY TO 9 PM TUESDAY.

     GALE WATCH...LMZ261-LMZ362-LMZ364-LMZ366-LMZ563-LMZ565...5 AM
     TUESDAY TO 9 PM TUESDAY.

&&

$$

000
FXUS63 KILX 051148
AFDILX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LINCOLN IL
648 AM CDT SUN SEP 5 2010

.DISCUSSION...
ISSUED 330 AM CDT SUN SEP 5 2010

00Z MODELS REMAIN IN FAIR AGREEMENT NEXT FEW DAYS THEN DIVERGE
LATER IN THE WEEK. MODELS CONTINUE TO SHOW STRONG LOW PRESSURE
PASSING WELL NORTH OF IL MON NIGHT/TUE WITH WEAKENING FRONT MOVING
THROUGH CENTRAL/SE IL WITH BREEZY CONDITIONS AND LITTLE OR NO QPF
DUE TO VERY LIMITED MOISTURE. LEANED ON THE WARMER MAV HIGHS NEXT
FEW DAYS WHICH HAVE BETTER TRACK RECORD.

SHORT TERM...TODAY THROUGH TUESDAY NIGHT.

WEAK HIGH PRESSURE 1017 MB OVER THE OHIO AND MID MS VALLEYS
PROVIDING CLEAR SKIES AND CALM WINDS OVER CENTRAL/SE IL EARLY
THIS MORNING. COOL FALL LIKE TEMPS IN THE UPPER 40S AND LOWER 50S
AND COOLEST MORNING SINCE MAY 19TH.

ANOTHER NICE DAY AHEAD WITH PARTLY TO MOSTLY SUNNY SKIES AND
MILDER HIGHS IN THE UPPER 70S TO NEAR 80F. WEAK HIGH PRESSURE OVER
THE OHIO VALLEY TO DRIFT EAST INTO THE MID ATLANTIC STATES TONIGHT
WHILE LOW PRESSURE DEEPENS OVER NEBRASKA. STRONG UPPER LEVEL LOW
ALONG THE ALBERTA AND SASKATCHEWAN PROVINCE LINE DIGS INTO THE
NORTHERN PLAINS MON AND BRINGS DEEP LOW PRESSURE INTO THE UPPER MS
VALLEY. TIGHTENING PRESSURE GRADIENT OVER IL MON WITH INCREASING
SSW WINDS BRINGING WARMER AIR WITH HIGHS IN THE MID 80S CENTRAL IL
AND UPPER 80S SE IL.

MODELS HAVE TRENDED QUICKER WITH FRONT MOVING THROUGH IL OVERNIGHT
MON NIGHT AND TUE MORNING AND GENERALLY COMES THROUGH DRY WITH
LIMITED MOISTURE TO WORK WITH AND UPPER LEVEL DYNAMICS PASSING
WELL NORTH OF CENTRAL IL OVER THE UPPER GREAT LAKES. HAVE JUST
SLIGHT CHANCE AT BEST OVER THE IL RIVER VALLEY AFTER MIDNIGHT MON
NIGHT AND OVER REST OF AREA TUE. WITH FASTER MOVEMENT OF FRONT
COOLED HIGHS A BIT ON TUE WITH AROUND 80F OVER THE IL RIVER VALLEY
AND NEAR 90F AT LAWRENCEVILLE. STILL BREEZY TUE WITH STRONG LOW
PRESSURE PASSING JUST NORTH OF MI.

LONG TERM...WEDNESDAY THROUGH SATURDAY.

EXTENDED MODELS BUILD UPPER LEVEL RIDGE INTO THE MS VALLEY WED-FRI
WHICH SHOULD ALLOW TEMPS TO MODIFY AGAIN DURING THIS TIME FRAME
WITH MID TO UPPER 80S FRI/SAT AND LAWRENCEVILLE NEAR 90F.
MOISTURE FROM THE WESTERN GULF LIFTING NORTHWARD INTO THE OZARKS
WED AND POSSIBLY INTO CENTRAL/SOUTHERN IL THU. CONTINUED TO HAVE
20-30% CHANCES SW AREAS WED AND ACROSS AREA THU.

HUETTL
&&

.AVIATION...
ISSUED 648 AM CDT SUN SEP 5 2010

MAINLY QUIET/VFR AVIATION WEATHER CONDITIONS EXPECTED THROUGH THE
12Z TAF VALID TIME. A RIDGE OF HIGH PRESSURE HAS SHIFTED JUST EAST
OF THE CENTRAL ILLINOIS TERMINALS...WITH SOUTHERLY WINDS
ANTICIPATED ON ITS BACK SIDE TODAY. SOME GUSTS ARE POSSIBLE DURING
PEAK DIURNAL HEATING...BUT THEY SHOULD GENERALLY BE AOB 20 KTS.
LLWS IS EXPECTED TO DEVELOP TONIGHT AS SURFACE WINDS DECOUPLE AND A
LOW LEVEL JET DEVELOPS JUST OFF THE SURFACE. OTHERWISE...CLOUD
COVER SHOULD BE MINIMAL INITIALLY...WITH HIGH BASED VFR CIGS
DEVELOPING TONIGHT IN ADVANCE OF A DEVELOPING FRONTAL SYSTEM IN
THE PLAINS.

BAK
&&

.ILX WATCHES/WARNINGS/ADVISORIES...
NONE.
&&

$$

000
FXUS63 KLOT 051124
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
624 AM CDT SUN SEP 5 2010

.DISCUSSION...
339 AM CDT

WHILE CHANCES OF ANY APPRECIABLE PRECIPITATION ARE RATHER LOW FOR
THE LOCAL AREA OVER THE NEXT SEVERAL DAYS...PATTERN WILL BE FAIRLY
ACTIVE IN TERMS OF A VIGOROUS STORM SYSTEM TRACKING JUST NORTH OF
THE AREA THAT WILL BRING SOME MODERATING TEMPERATURES FOR MONDAY
AHEAD OF THE COLD FRONT...AND SOME WINDY CONDITIONS FOR MONDAY AND
TUESDAY.

IN THE NEAR TERM...QUIET WEATHER CONTINUES FOR THE LOCAL AREA AND
THE MOST INTERESTING WEATHER FEATURE TO WATCH FOR TODAY WILL BE MID
LEVEL CLOUDS INCREASING ACROSS THE AREA. IR SATELLITE IMAGERY OVER
PAST 1 TO 2 HOURS BEGINNING TO SHOW BLOSSOMING MID LEVEL CLOUD FROM
SOUTHWEST MINNESOTA INTO SOUTHEAST IOWA AT NOSE OF STRONGER MID
LEVEL WARM ADVECTION. MODELS SEEM TO HAVE HANDLED THIS INCREASING
MID LEVEL RH FAIRLY WELL THIS MORNING...AND SHOULD GRADUALLY SEE THIS
EXPANDING MID DECK WORK ITS WAY INTO NORTHERN ILLINOIS LATER THIS
MORNING AND THIS AFTERNOON.

SOME UPPER FORCING TO INCREASE ACROSS THE AREA THIS AFTERNOON AS A
VORT MAX ACROSS EASTERN SOUTH DAKOTA/EASTERN NEBRASKA PROGRESSES
THOUGH THE UPPER RIDGE AND INTO NORTHERN ILLINOIS. AS THIS
OCCURS...ISENTROPIC UPGLIDE WILL RAMP UP...ESPECIALLY TOWARD
EVENING. ANALYSIS OF NAM/GFS 305K ISENTROPIC SURFACES STILL
INDICATING THIS STRONGEST UPGLIDE ACROSS APPROX NORTHERN ONE
THIRD OF THE FORECAST AREA. EVEN WITH THIS UPGLIDE...CONDENSATIONAL
PRESSURE DEFICITS ON THIS SURFACE STILL 100-150 MB...WITH THE
LOWER VALUES FURTHER TO NORTH FROM CENTRAL WISCONSIN INTO CENTRAL
LOWER MICHIGAN. PRECIPITATION PROB STILL LOOKING QUITE MEAGER
TODAY. EVEN THOUGH SOUTHERLY LOW LEVEL FLOW WILL RAMP UP LATER
THIS AFTERNOON...UPSTREAM MOISTURE PROFILES PER 00Z RAOBS FROM
LAST EVENING ARE NOTHING IMPRESSIVE WITH 850 HPA DEW PTS OF -2 DEG
CELSIUS AT KLZK AND +5 DEG CELSIUS AT KSGF. GIVEN STRENGTH OF
ISENTROPIC UPGLIDE...DID NOT WANT TO COMPLETELY REMOVE POPS FOR
TONIGHT...ALTHOUGH WITH SUCH DRY LOW LEVELS WILL TONE DOWN MENTION
TO SLIGHT CHANCE OF LIGHT RAIN SHOWERS OR SPRINKLES. EXPECTING
TEMPERATURES TODAY TO BE 5 TO 10 DEGREES WARMER THAN YESTERDAY AND
THE MAGNITUDE OF MODERATION TODAY WILL BE SOMEWHAT CONTROLLED BY
EXTENT AND TIMING OF MID LEVEL CLOUD INCREASE THIS AFTERNOON.

BY 12Z MONDAY...FOCUS FOR STRONGER ISENTROPIC LIFT WILL SHIFT
NORTHWARD INTO SOUTHERN/CENTRAL WISCONSIN WITH LOW LEVEL WARM FRONT...
SO HAVE MADE NO CHANGES TO A DRY MONDAY FORECAST AS SOME OF THAT
FAIRLY DRY LOW LEVEL AIR CURRENTLY ACROSS LOWER MS RIVER VALLEY
ADVECTS NORTHWARD. MAIN AXIS OF MOISTURE TRANSPORT MONDAY WILL
OCCUR TO THE WEST ACROSS THE CENTRAL AND NORTHERN PLAINS AS
THE VIGOROUS UPPER LEVEL TROUGH TRACKS EAST OUT OF THE ROCKIES.
WITH LOW LEVEL RIDGE ACROSS LOWER MS RVR VALLEY BEING SLOW TO
TRUDGE EASTWARD...IT STILL APPEARS AS THOUGH MORE SIGNIFICANT LOW
LEVEL MOISTURE WILL BE CONFINED TO NARROW FRONTAL AXIS ONCE AGAIN
AND ANY CHANCE OF PRECIP FOR LOCAL AREA WILL HOLD OFF UNTIL MONDAY
NIGHT AS FRONT APPROACHES. OTHERWISE...MONDAY LOOKING TO BE QUITE
WARM WITH ABOVE NORMAL HIGHS REACHING INTO THE LOWER TO MID 80S
FOR THE AREA WITH SOUTH GUSTS OF 30 TO 35 MPH POSSIBLE IN THE
AFTERNOON. MODELS ARE IN GENERAL AGREEMENT IN OCCLUDING SYSTEM
MONDAY NIGHT INTO EARLY TUESDAY WITH INITIALLY BETTER UPPER
DYNAMICS/LOW LEVEL CONVG MONDAY AFTERNOON/EARLY EVENING SETTING UP
ACROSS PORTIONS OF IOWA/SOUTHERN MINNESOTA. AT THIS TIME...STILL
FEEL BETTER CONVECTIVE CHANCES WILL BE GENERALLY WEST OF MS
RIVER...ALTHOUGH WILL MAINTAIN SLIGHT CHANCE POPS FOR THUNDER FROM
WEST TO EAST MONDAY NIGHT.

SYSTEM WILL SLOWLY FILL TUESDAY AS DRY LOW/MID LEVEL AIR WORKS
INTO THE AREA. THERE MAY BE SOME ISOLD SHOWERS ALONG THE FRONT
EARLY TUESDAY ACROSS SOUTHEASTERN PORTIONS OF THE AREA...BUT
OVERWHELMING DRY AIR ADVECTION ACROSS THE AREA SHOULD RESULT IN
DRY AND VERY WINDY CONDITIONS FOR TUES AFTERNOON. COLD ADVECTION
TUESDAY AFTERNOON WILL ALLOW FOR MORE SUBSTANTIAL MIXED LAYER
DEPTHS AND EVEN SOME CONCERN FOR NUDGING UP AGAINST WIND ADVISORY
CRITERIA AND WILL INCLUDE MENTION OF THESE EXPECTED VERY WINDY
CONDITIONS IN THIS MORNINGS HWO. TEMPS RATHER TRICKY ON TUESDAY
WITH COLD ADVECTION FIGHTING THE EFFECTS OF DEEPER MIXING. MAY BE
A BIT WARM WITH HIGHS TUESDAY RANGING FROM MID 70S FAR NORTH
CENTRAL ILLINOIS TO LOWER 80S FAR SOUTHEAST...BUT THIS DOES APPEAR
TO BE A COMMON SETUP WHEN THE EFFECTS OF SUBSIDENCE/MIXING DO
ALLOW FOR WARMER THAN EXPECTED TEMPS...SO HAVE NOT CHANGED THESE
HIGHS MUCH AT THIS POINT WITH STILL SOME SUBTLE MODEL DIFFERENCES
IN TIMING THIS COLD ADVECTION.

WEATHER TO FINALLY QUIET DOWN TUESDAY NIGHT INTO WEDNESDAY AS NEXT
SFC HIGH SLIDES INTO THE REGION. LOW LEVEL FRONT NOT EXPECTED TO BE
TOO FAR SOUTH OF THE AREA...ALTHOUGH NOT EXPECTING THIS LOW LEVEL
BAROCLINIC ZONE TO BE ACTIVE WITH ANY PRECIP DUE TO LIMITED
MOISTURE. NEW MEDIUM RANGE MODELS STILL SUPPORT THE GOING EXTENDED
FORECAST OF CHANCES OF THUNDER LATE THURSDAY/FRIDAY WITH RENEWED
THETA-E ADVECTION IN ADVANCE OF NEXT SIGNIFICANT UPPER TROUGH
WORKING THROUGH NWRN CONUS. THIS PATTERN SHOULD ALSO ALLOW MUCH OF
THE AREA TO POTENTIALLY WARM BACK INTO THE LOWER 80S TOWARD THE END
OF THE WEEK.

MARSILI

&&

.FIRE WEATHER...
330 AM CDT

SFC PRESSURE GRADIENT WILL STRENGTHEN ON MONDAY AS STRONG SFC LOW
MOVES INTO SOUTHERN MINNESOTA. STILL SOME UNCERTAINTY REMAINS AS
TO MIXING HEIGHTS MONDAY AFTERNOON AND EXACTLY HOW MUCH LOW LEVEL
DRY AIR CAN MIX DOWN TO THE SURFACE. FORECASTED HIGHS INTO THE
LOWER TO MID 80S COMBINED WITH DEW PTS LIKELY MIXING OUT TO AROUND
50 WOULD SUPPORT MIN AFTERNOON RELATIVE HUMIDITIES AROUND 30
PERCENT. WHILE WIND GUSTS SHOULD BE UP AROUND 30 MPH MONDAY
AFTERNOON...ENOUGH UNCERTAINTY EXISTS WITH REGARDS TO MIXING AND
FUEL MOISTURES TO HOLD OFF ON ANY FIRE WEATHER HEADLINES AT THIS
TIME.

TUESDAY IS SHAPING UP AS ANOTHER DAY OF POTENTIAL FIRE WEATHER
CONCERN AS CONFIDENCE IN DEEPER MIXED LAYER IS HIGHER ALONG WITH
POTENTIAL OF SOME SOUTHWEST WIND GUSTS TO 40 TO 45 MPH. IN
CONTRAST TO MONDAY THE MAIN ELEMENT OF UNCERTAINTY WITH HOW LOW
AFTERNOON RELATIVE HUMIDITIES CAN REACH IS JUST HOW HIGH THE
TEMPERATURE WILL CLIMB. AT THIS TIME...HAVE FORECASTED MIN
AFTERNOON RELATIVE HUMIDITIES IN THE 30 TO 35 PERCENT RANGE BUT
THIS WILL NEED TO BE MONITORED FOR ANY CHANGES TO FUTURE
FORECASTS. ALSO IF FRONTAL PASSAGE DOES COME THROUGH DRY MONDAY
NIGHT INTO TUESDAY...FUEL MOISTURES WILL BE SOMEWHAT LOWER WHICH
WOULD INCREASE FIRE WEATHER RISK FOR TUESDAY.

MARSILI

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 12Z...

POTENTIAL OF LOW LEVEL WIND SHEAR LATE TONIGHT.

MARSILI

//DISCUSSION...UPDATED 12Z...

SFC RIDGE AXIS OVERHEAD EARLY THIS MORNING WILL SHIFT OFF TO THE
EAST AND PROVIDE SOUTHERLY WINDS AROUND 10 KNOTS BY MID TO LATE
MORNING. SATELLITE IMAGERY EARLY THIS MORNING INDICATES EXPANDING
MID LEVEL CLOUDINESS DUE TO WARM ADVECTION...AND THESE MID LEVEL
CLOUDS SHOULD CONTINUE TO WORK EASTWARD THIS MORNING INTO NORTHERN
ILLINOIS. BY LATE TONIGHT...WARM ADVECTION UNDER THIS STRONG
SOUTHERLY LOW LEVEL JET AND BOUNDARY LAYER DECOUPLING WILL ALLOW
FOR THE POSSIBILITY OF LOW LEVEL WIND SHEAR AND HAVE NOT MADE ANY
SIGNIFICANT CHANGES FROM PREVIOUS TAF IN THIS REGARD. THREAT OF
LOW LEVEL WIND SHEAR WILL DIMINISH IN THE 13Z-15Z MONDAY TIMEFRAME
AS MIXING COMMENCES...WITH SOME GUSTS INTO THE 20 TO 25 KT RANGE
POSSIBLE BY MID TO LATE MORNING MONDAY. WILL CONTINUE TO KEEP
TAFS DRY TONIGHT AS ANY MOISTURE INCREASES WILL BE MORE MID LEVEL IN
NATURE MAKING IT HARD TO REALIZE ANY KIND OF SIGNIFICANT
INSTABILITY.

MARSILI

//ORD AND MDW CONFIDENCE...UPDATED 12Z...

MEDIUM CONFIDENCE IN MEETING LOW LEVEL WIND SHEAR CRITERIA LATE
TONIGHT...MAINLY AFTER 04Z.

HIGH CONFIDENCE IN ALL OTHER ASPECTS OF FORECAST.

MARSILI

//OUTLOOK FOR ORD/MDW FOR 18Z MONDAY-12Z FRIDAY...UPDATED 06Z...

MONDAY...VFR. SOUTH WIND GUSTS OVER 30KT POSSIBLE DURING DAYTIME.
TUESDAY...VFR. SOUTHWEST->WEST WIND GUSTS OVER 30KT DURING DAYTIME.
WEDNESDAY...VFR.
THURSDAY AND FRIDAY...SLIGHT CHANCE OF TSRA OTHERWISE VFR.

IZZI

&&

.MARINE...
330 AM CDT

STILL SEEING SOME ACCELERATION OF THE WINDS THIS MORNING OVER
EASTERN PORTIONS OF THE LAKE NEAR THE LAKE INSTABILITY INDUCED
CONVERGENCE BANDS. THOSE LOCALIZED WIND MAXIMA WILL FADE AFTER
SUNRISE WITH GRADIENT RELAXING AND WINDS BACKING IN ADVANCE OF THE
NEXT STORM SYSTEM.

MODEL GUIDANCE REMAINS IN EXCELLENT AGREEMENT ON TRACKING A DEEP LOW
FROM THE HIGH PLAINS THIS EVENING TO LAKE SUPERIOR BY TUESDAY
MORNING. VERY STRONG PRESSURE GRADIENT ASSOCIATED WITH THIS LARGE
AND RATHER INTENSE LOW SHOULD RESULT IN AN EXTENDED PERIOD OF HIGH
WINDS/WAVES. FORECAST SOUNDINGS FROM THE GFS/WRF-NAM BOTH CONTINUE
TO SUGGEST SUFFICIENTLY STEEP LOW LEVEL LAPSE RATES MONDAY INTO
MONDAY EVENING TO TAP INTO THE GALE FORCE WINDS ALOFT...HOWEVER
STRONGLY SUSPECT THAT WATER TEMPS IN THE MODELS ARE TOO WARM AND DO
NOT ACCOUNT FOR THE RECENT UPWELLING THAT HAS OCCURRED. MODEL 2M
TEMPS ARE PROGGED TO GET INTO THE MID-UPPER 70S OVER THE LAKE AND
INTO THE 80S OVER LAND...WHICH BEING ADVECTED OVER TOP THE UPPER
60/NEAR 70F WATERS SHOULD RESULT IN A NOTICEABLY MORE STABLE MARINE
LAYER MONDAY INTO MONDAY EVENING. FOR THIS REASON HAVE UNDERCUT
MODEL WINDS AND PARTICULARLY GUSTS AND HELD SPEEDS JUST BELOW GALE
FORCE THRU MON EVENING.

LATER MONDAY NIGHT INTO TUESDAY AS OCCLUDED FRONT MOVE THROUGH
EXPECT COLD AIR ADVECTION TO STEEPEN UP THE LAPSE RATES AND ALLOW
WINDS TO REALLY RAMP UP OVER THE LAKE. WHILE LOW WILL BE IN A
WEAKENING PHASE TUESDAY...THAT WILL ACTUALLY ONLY WORK TO ENHANCE
THE PRESSURE RISES AS THE LOW PULLS OFF TO THE EAST. GIVEN
THIS...HAVE FOLLOWED MODEL GUIDANCE WHICH IS IN GOOD AGREEMENT ON
GALES DEVELOPING LATE MONDAY NIGHT AND LASTING UNTIL TUESDAY
EVENING. GIVEN THE STRONG MODEL CONSENSUS AND RUN-TO-RUN CONSISTENCY
HAVE GONE AHEAD AND HOISTED A GALE WATCH FOR THE OPEN LAKE FOR LATE
MON NIGHT INTO TUESDAY. GALE WATCH MAY WELL NEED TO BE EXPANDED INTO
THE NEARSHORE WATERS AS WELL...BUT THAT WILL BE A 5TH PERIOD EVENT
AND WITH SLIGHTLY LESSER CONFIDENCE THAN OVER THE OPEN LAKE WILL
PUNT THAT DECISION TO THE LATER SHIFTS.

IZZI

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...GALE WATCH...LMZ080-LMZ567-LMZ669-LMZ671-LMZ673-LMZ675-LMZ777-
     LMZ779-LMZ868-LMZ870-LMZ872-LMZ874-LMZ876-LMZ878...MIDNIGHT
     TUESDAY TO 9 PM TUESDAY.

     GALE WATCH...LMZ261-LMZ362-LMZ364-LMZ366-LMZ563-LMZ565...5 AM
     TUESDAY TO 9 PM TUESDAY.

&&

$$

000
FXUS63 KLOT 050855
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
355 AM CDT SUN SEP 5 2010

.DISCUSSION...
339 AM CDT

WHILE CHANCES OF ANY APPRECIABLE PRECIPITATION ARE RATHER LOW FOR
THE LOCAL AREA OVER THE NEXT SEVERAL DAYS...PATTERN WILL BE FAIRLY
ACTIVE IN TERMS OF A VIGOROUS STORM SYSTEM TRACKING JUST NORTH OF
THE AREA THAT WILL BRING SOME MODERATING TEMPERATURES FOR MONDAY
AHEAD OF THE COLD FRONT...AND SOME WINDY CONDITIONS FOR MONDAY AND
TUESDAY.

IN THE NEAR TERM...QUIET WEATHER CONTINUES FOR THE LOCAL AREA AND
THE MOST INTERESTING WEATHER FEATURE TO WATCH FOR TODAY WILL BE MID
LEVEL CLOUDS INCREASING ACROSS THE AREA. IR SATELLITE IMAGERY OVER
PAST 1 TO 2 HOURS BEGINNING TO SHOW BLOSSOMING MID LEVEL CLOUD FROM
SOUTHWEST MINNESOTA INTO SOUTHEAST IOWA AT NOSE OF STRONGER MID
LEVEL WARM ADVECTION. MODELS SEEM TO HAVE HANDLED THIS INCREASING
MID LEVEL RH FAIRLY WELL THIS MORNING...AND SHOULD GRADUALLY SEE THIS
EXPANDING MID DECK WORK ITS WAY INTO NORTHERN ILLINOIS LATER THIS
MORNING AND THIS AFTERNOON.

SOME UPPER FORCING TO INCREASE ACROSS THE AREA THIS AFTERNOON AS A
VORT MAX ACROSS EASTERN SOUTH DAKOTA/EASTERN NEBRASKA PROGRESSES
THOUGH THE UPPER RIDGE AND INTO NORTHERN ILLINOIS. AS THIS
OCCURS...ISENTROPIC UPGLIDE WILL RAMP UP...ESPECIALLY TOWARD
EVENING. ANALYSIS OF NAM/GFS 305K ISENTROPIC SURFACES STILL
INDICATING THIS STRONGEST UPGLIDE ACROSS APPROX NORTHERN ONE
THIRD OF THE FORECAST AREA. EVEN WITH THIS UPGLIDE...CONDENSATIONAL
PRESSURE DEFICITS ON THIS SURFACE STILL 100-150 MB...WITH THE
LOWER VALUES FURTHER TO NORTH FROM CENTRAL WISCONSIN INTO CENTRAL
LOWER MICHIGAN. PRECIPITATION PROB STILL LOOKING QUITE MEAGER
TODAY. EVEN THOUGH SOUTHERLY LOW LEVEL FLOW WILL RAMP UP LATER
THIS AFTERNOON...UPSTREAM MOISTURE PROFILES PER 00Z RAOBS FROM
LAST EVENING ARE NOTHING IMPRESSIVE WITH 850 HPA DEW PTS OF -2 DEG
CELSIUS AT KLZK AND +5 DEG CELSIUS AT KSGF. GIVEN STRENGTH OF
ISENTROPIC UPGLIDE...DID NOT WANT TO COMPLETELY REMOVE POPS FOR
TONIGHT...ALTHOUGH WITH SUCH DRY LOW LEVELS WILL TONE DOWN MENTION
TO SLIGHT CHANCE OF LIGHT RAIN SHOWERS OR SPRINKLES. EXPECTING
TEMPERATURES TODAY TO BE 5 TO 10 DEGREES WARMER THAN YESTERDAY AND
THE MAGNITUDE OF MODERATION TODAY WILL BE SOMEWHAT CONTROLLED BY
EXTENT AND TIMING OF MID LEVEL CLOUD INCREASE THIS AFTERNOON.

BY 12Z MONDAY...FOCUS FOR STRONGER ISENTROPIC LIFT WILL SHIFT
NORTHWARD INTO SOUTHERN/CENTRAL WISCONSIN WITH LOW LEVEL WARM FRONT...
SO HAVE MADE NO CHANGES TO A DRY MONDAY FORECAST AS SOME OF THAT
FAIRLY DRY LOW LEVEL AIR CURRENTLY ACROSS LOWER MS RIVER VALLEY
ADVECTS NORTHWARD. MAIN AXIS OF MOISTURE TRANSPORT MONDAY WILL
OCCUR TO THE WEST ACROSS THE CENTRAL AND NORTHERN PLAINS AS
THE VIGOROUS UPPER LEVEL TROUGH TRACKS EAST OUT OF THE ROCKIES.
WITH LOW LEVEL RIDGE ACROSS LOWER MS RVR VALLEY BEING SLOW TO
TRUDGE EASTWARD...IT STILL APPEARS AS THOUGH MORE SIGNIFICANT LOW
LEVEL MOISTURE WILL BE CONFINED TO NARROW FRONTAL AXIS ONCE AGAIN
AND ANY CHANCE OF PRECIP FOR LOCAL AREA WILL HOLD OFF UNTIL MONDAY
NIGHT AS FRONT APPROACHES. OTHERWISE...MONDAY LOOKING TO BE QUITE
WARM WITH ABOVE NORMAL HIGHS REACHING INTO THE LOWER TO MID 80S
FOR THE AREA WITH SOUTH GUSTS OF 30 TO 35 MPH POSSIBLE IN THE
AFTERNOON. MODELS ARE IN GENERAL AGREEMENT IN OCCLUDING SYSTEM
MONDAY NIGHT INTO EARLY TUESDAY WITH INITIALLY BETTER UPPER
DYNAMICS/LOW LEVEL CONVG MONDAY AFTERNOON/EARLY EVENING SETTING UP
ACROSS PORTIONS OF IOWA/SOUTHERN MINNESOTA. AT THIS TIME...STILL
FEEL BETTER CONVECTIVE CHANCES WILL BE GENERALLY WEST OF MS
RIVER...ALTHOUGH WILL MAINTAIN SLIGHT CHANCE POPS FOR THUNDER FROM
WEST TO EAST MONDAY NIGHT.

SYSTEM WILL SLOWLY FILL TUESDAY AS DRY LOW/MID LEVEL AIR WORKS
INTO THE AREA. THERE MAY BE SOME ISOLD SHOWERS ALONG THE FRONT
EARLY TUESDAY ACROSS SOUTHEASTERN PORTIONS OF THE AREA...BUT
OVERWHELMING DRY AIR ADVECTION ACROSS THE AREA SHOULD RESULT IN
DRY AND VERY WINDY CONDITIONS FOR TUES AFTERNOON. COLD ADVECTION
TUESDAY AFTERNOON WILL ALLOW FOR MORE SUBSTANTIAL MIXED LAYER
DEPTHS AND EVEN SOME CONCERN FOR NUDGING UP AGAINST WIND ADVISORY
CRITERIA AND WILL INCLUDE MENTION OF THESE EXPECTED VERY WINDY
CONDITIONS IN THIS MORNINGS HWO. TEMPS RATHER TRICKY ON TUESDAY
WITH COLD ADVECTION FIGHTING THE EFFECTS OF DEEPER MIXING. MAY BE
A BIT WARM WITH HIGHS TUESDAY RANGING FROM MID 70S FAR NORTH
CENTRAL ILLINOIS TO LOWER 80S FAR SOUTHEAST...BUT THIS DOES APPEAR
TO BE A COMMON SETUP WHEN THE EFFECTS OF SUBSIDENCE/MIXING DO
ALLOW FOR WARMER THAN EXPECTED TEMPS...SO HAVE NOT CHANGED THESE
HIGHS MUCH AT THIS POINT WITH STILL SOME SUBTLE MODEL DIFFERENCES
IN TIMING THIS COLD ADVECTION.

WEATHER TO FINALLY QUIET DOWN TUESDAY NIGHT INTO WEDNESDAY AS NEXT
SFC HIGH SLIDES INTO THE REGION. LOW LEVEL FRONT NOT EXPECTED TO BE
TOO FAR SOUTH OF THE AREA...ALTHOUGH NOT EXPECTING THIS LOW LEVEL
BAROCLINIC ZONE TO BE ACTIVE WITH ANY PRECIP DUE TO LIMITED
MOISTURE. NEW MEDIUM RANGE MODELS STILL SUPPORT THE GOING EXTENDED
FORECAST OF CHANCES OF THUNDER LATE THURSDAY/FRIDAY WITH RENEWED
THETA-E ADVECTION IN ADVANCE OF NEXT SIGNIFICANT UPPER TROUGH
WORKING THROUGH NWRN CONUS. THIS PATTERN SHOULD ALSO ALLOW MUCH OF
THE AREA TO POTENTIALLY WARM BACK INTO THE LOWER 80S TOWARD THE END
OF THE WEEK.

&&

.FIRE WEATHER...
330 AM CDT

SFC PRESSURE GRADIENT WILL STRENGTHEN ON MONDAY AS STRONG SFC LOW
MOVES INTO SOUTHERN MINNESOTA. STILL SOME UNCERTAINTY REMAINS AS
TO MIXING HEIGHTS MONDAY AFTERNOON AND EXACTLY HOW MUCH LOW LEVEL
DRY AIR CAN MIX DOWN TO THE SURFACE. FORECASTED HIGHS INTO THE
LOWER TO MID 80S COMBINED WITH DEW PTS LIKELY MIXING OUT TO AROUND
50 WOULD SUPPORT MIN AFTERNOON RELATIVE HUMIDITIES AROUND 30
PERCENT. WHILE WIND GUSTS SHOULD BE UP AROUND 30 MPH MONDAY
AFTERNOON...ENOUGH UNCERTAINTY EXISTS WITH REGARDS TO MIXING AND
FUEL MOISTURES TO HOLD OFF ON ANY FIRE WEATHER HEADLINES AT THIS
TIME.

TUESDAY IS SHAPING UP AS ANOTHER DAY OF POTENTIAL FIRE WEATHER
CONCERN AS CONFIDENCE IN DEEPER MIXED LAYER IS HIGHER ALONG WITH
POTENTIAL OF SOME SOUTHWEST WIND GUSTS TO 40 TO 45 MPH. IN
CONTRAST TO MONDAY THE MAIN ELEMENT OF UNCERTAINTY WITH HOW LOW
AFTERNOON RELATIVE HUMIDITIES CAN REACH IS JUST HOW HIGH THE
TEMPERATURE WILL CLIMB. AT THIS TIME...HAVE FORECASTED MIN
AFTERNOON RELATIVE HUMIDITIES IN THE 30 TO 35 PERCENT RANGE BUT
THIS WILL NEED TO BE MONITORED FOR ANY CHANGES TO FUTURE
FORECASTS. ALSO IF FRONTAL PASSAGE DOES COME THROUGH DRY MONDAY
NIGHT INTO TUESDAY...FUEL MOISTURES WILL BE SOMEWHAT LOWER WHICH
WOULD INCREASE FIRE WEATHER RISK FOR TUESDAY.

MARSILI

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 09Z...

NONE.

IZZI

//DISCUSSION...UPDATED 06Z...

SKC WITH LIGHT WINDS OVERNIGHT. SOUTH TO SOUTHWEST WINDS DEVELOP
BY LATE MORNING SUNDAY WITH AN INCREASE IN MID LEVEL CLOUDS
EXPECTED IN ADVANCE OF A DEVELOPING WEAK SHORTWAVE SUNDAY
AFTERNOON. DEEPENING LOW PRESSURE OVER THE PLAINS SUNDAY NIGHT
SHOULD RESULT IN STRONG LOW LEVEL JET SUNDAY NIGHT WITH FORECAST
SOUNDINGS SUGGESTING A SHARP NEAR SFC INVERSION FAVORABLE FOR
LLWS. LOW LEVEL MOISTURE LOOKS TOO SCANT FOR PRECIP WITH JUST A
REMOTE CHANCE OF A SPRINKLE FROM THE MID LEVEL DECK SUN EVENING.

IZZI

//ORD AND MDW CONFIDENCE...UPDATED 09Z...

HIGH CONFIDENCE IN ALL ASPECTS OF THE TAFS.

IZZI

//OUTLOOK FOR ORD/MDW FOR 12Z MONDAY-12Z SATURDAY...UPDATED 06Z...

MONDAY...VFR. SOUTH WIND GUSTS OVER 30KT POSSIBLE DURING DAYTIME.
TUESDAY...VFR. SOUTHWEST->WEST WIND GUSTS OVER 30KT DURING DAYTIME.
WEDNESDAY...VFR.
THURSDAY AND FRIDAY...SLIGHT CHANCE OF TSRA OTHERWISE VFR.

IZZI

&&

.MARINE...
330 AM CDT

STILL SEEING SOME ACCELERATION OF THE WINDS THIS MORNING OVER
EASTERN PORTIONS OF THE LAKE NEAR THE LAKE INSTABILITY INDUCED
CONVERGENCE BANDS. THOSE LOCALIZED WIND MAXIMA WILL FADE AFTER
SUNRISE WITH GRADIENT RELAXING AND WINDS BACKING IN ADVANCE OF THE
NEXT STORM SYSTEM.

MODEL GUIDANCE REMAINS IN EXCELLENT AGREEMENT ON TRACKING A DEEP LOW
FROM THE HIGH PLAINS THIS EVENING TO LAKE SUPERIOR BY TUESDAY
MORNING. VERY STRONG PRESSURE GRADIENT ASSOCIATED WITH THIS LARGE
AND RATHER INTENSE LOW SHOULD RESULT IN AN EXTENDED PERIOD OF HIGH
WINDS/WAVES. FORECAST SOUNDINGS FROM THE GFS/WRF-NAM BOTH CONTINUE
TO SUGGEST SUFFICIENTLY STEEP LOW LEVEL LAPSE RATES MONDAY INTO
MONDAY EVENING TO TAP INTO THE GALE FORCE WINDS ALOFT...HOWEVER
STRONGLY SUSPECT THAT WATER TEMPS IN THE MODELS ARE TOO WARM AND DO
NOT ACCOUNT FOR THE RECENT UPWELLING THAT HAS OCCURRED. MODEL 2M
TEMPS ARE PROGGED TO GET INTO THE MID-UPPER 70S OVER THE LAKE AND
INTO THE 80S OVER LAND...WHICH BEING ADVECTED OVER TOP THE UPPER
60/NEAR 70F WATERS SHOULD RESULT IN A NOTICEABLY MORE STABLE MARINE
LAYER MONDAY INTO MONDAY EVENING. FOR THIS REASON HAVE UNDERCUT
MODEL WINDS AND PARTICULARLY GUSTS AND HELD SPEEDS JUST BELOW GALE
FORCE THRU MON EVENING.

LATER MONDAY NIGHT INTO TUESDAY AS OCCLUDED FRONT MOVE THROUGH
EXPECT COLD AIR ADVECTION TO STEEPEN UP THE LAPSE RATES AND ALLOW
WINDS TO REALLY RAMP UP OVER THE LAKE. WHILE LOW WILL BE IN A
WEAKENING PHASE TUESDAY...THAT WILL ACTUALLY ONLY WORK TO ENHANCE
THE PRESSURE RISES AS THE LOW PULLS OFF TO THE EAST. GIVEN
THIS...HAVE FOLLOWED MODEL GUIDANCE WHICH IS IN GOOD AGREEMENT ON
GALES DEVELOPING LATE MONDAY NIGHT AND LASTING UNTIL TUESDAY
EVENING. GIVEN THE STRONG MODEL CONSENSUS AND RUN-TO-RUN CONSISTENCY
HAVE GONE AHEAD AND HOISTED A GALE WATCH FOR THE OPEN LAKE FOR LATE
MON NIGHT INTO TUESDAY. GALE WATCH MAY WELL NEED TO BE EXPANDED INTO
THE NEARSHORE WATERS AS WELL...BUT THAT WILL BE A 5TH PERIOD EVENT
AND WITH SLIGHTLY LESSER CONFIDENCE THAN OVER THE OPEN LAKE WILL
PUNT THAT DECISION TO THE LATER SHIFTS.

IZZI

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...GALE WATCH...LMZ080-LMZ567-LMZ669-LMZ671-LMZ673-LMZ675-LMZ777-
     LMZ779-LMZ868-LMZ870-LMZ872-LMZ874-LMZ876-LMZ878...MIDNIGHT
     TUESDAY TO 9 PM TUESDAY.

     GALE WATCH...LMZ261-LMZ362-LMZ364-LMZ366-LMZ563-LMZ565...5 AM
     TUESDAY TO 9 PM TUESDAY.

&&

$$

000
FXUS63 KLOT 050839
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
339 AM CDT SUN SEP 5 2010

.DISCUSSION...
339 AM CDT

WHILE CHANCES OF ANY APPRECIABLE PRECIPITATION ARE RATHER LOW FOR
THE LOCAL AREA OVER THE NEXT SEVERAL DAYS...PATTERN WILL BE FAIRLY
ACTIVE IN TERMS OF A VIGOROUS STORM SYSTEM TRACKING JUST NORTH OF
THE AREA THAT WILL BRING SOME MODERATING TEMPERATURES FOR MONDAY
AHEAD OF THE COLD FRONT...AND SOME WINDY CONDITIONS FOR MONDAY AND
TUESDAY.

IN THE NEAR TERM...QUIET WEATHER CONTINUES FOR THE LOCAL AREA AND
THE MOST INTERESTING WEATHER FEATURE TO WATCH FOR TODAY WILL BE MID
LEVEL CLOUDS INCREASING ACROSS THE AREA. IR SATELLITE IMAGERY OVER
PAST 1 TO 2 HOURS BEGINNING TO SHOW BLOSSOMING MID LEVEL CLOUD FROM
SOUTHWEST MINNESOTA INTO SOUTHEAST IOWA AT NOSE OF STRONGER MID
LEVEL WARM ADVECTION. MODELS SEEM TO HAVE HANDLED THIS INCREASING
MID LEVEL RH FAIRLY WELL THIS MORNING...AND SHOULD GRADUALLY SEE THIS
EXPANDING MID DECK WORK ITS WAY INTO NORTHERN ILLINOIS LATER THIS
MORNING AND THIS AFTERNOON.

SOME UPPER FORCING TO INCREASE ACROSS THE AREA THIS AFTERNOON AS A
VORT MAX ACROSS EASTERN SOUTH DAKOTA/EASTERN NEBRASKA PROGRESSES
THOUGH THE UPPER RIDGE AND INTO NORTHERN ILLINOIS. AS THIS
OCCURS...ISENTROPIC UPGLIDE WILL RAMP UP...ESPECIALLY TOWARD
EVENING. ANALYSIS OF NAM/GFS 305K ISENTROPIC SURFACES STILL
INDICATING THIS STRONGEST UPGLIDE ACROSS APPROX NORTHERN ONE
THIRD OF THE FORECAST AREA. EVEN WITH THIS UPGLIDE...CONDENSATIONAL
PRESSURE DEFICITS ON THIS SURFACE STILL 100-150 MB...WITH THE
LOWER VALUES FURTHER TO NORTH FROM CENTRAL WISCONSIN INTO CENTRAL
LOWER MICHIGAN. PRECIPITATION PROB STILL LOOKING QUITE MEAGER
TODAY. EVEN THOUGH SOUTHERLY LOW LEVEL FLOW WILL RAMP UP LATER
THIS AFTERNOON...UPSTREAM MOISTURE PROFILES PER 00Z RAOBS FROM
LAST EVENING ARE NOTHING IMPRESSIVE WITH 850 HPA DEW PTS OF -2 DEG
CELSIUS AT KLZK AND +5 DEG CELSIUS AT KSGF. GIVEN STRENGTH OF
ISENTROPIC UPGLIDE...DID NOT WANT TO COMPLETELY REMOVE POPS FOR
TONIGHT...ALTHOUGH WITH SUCH DRY LOW LEVELS WILL TONE DOWN MENTION
TO SLIGHT CHANCE OF LIGHT RAIN SHOWERS OR SPRINKLES. EXPECTING
TEMPERATURES TODAY TO BE 5 TO 10 DEGREES WARMER THAN YESTERDAY AND
THE MAGNITUDE OF MODERATION TODAY WILL BE SOMEWHAT CONTROLLED BY
EXTENT AND TIMING OF MID LEVEL CLOUD INCREASE THIS AFTERNOON.

BY 12Z MONDAY...FOCUS FOR STRONGER ISENTROPIC LIFT WILL SHIFT
NORTHWARD INTO SOUTHERN/CENTRAL WISCONSIN WITH LOW LEVEL WARM FRONT...
SO HAVE MADE NO CHANGES TO A DRY MONDAY FORECAST AS SOME OF THAT
FAIRLY DRY LOW LEVEL AIR CURRENTLY ACROSS LOWER MS RIVER VALLEY
ADVECTS NORTHWARD. MAIN AXIS OF MOISTURE TRANSPORT MONDAY WILL
OCCUR TO THE WEST ACROSS THE CENTRAL AND NORTHERN PLAINS AS
THE VIGOROUS UPPER LEVEL TROUGH TRACKS EAST OUT OF THE ROCKIES.
WITH LOW LEVEL RIDGE ACROSS LOWER MS RVR VALLEY BEING SLOW TO
TRUDGE EASTWARD...IT STILL APPEARS AS THOUGH MORE SIGNIFICANT LOW
LEVEL MOISTURE WILL BE CONFINED TO NARROW FRONTAL AXIS ONCE AGAIN
AND ANY CHANCE OF PRECIP FOR LOCAL AREA WILL HOLD OFF UNTIL MONDAY
NIGHT AS FRONT APPROACHES. OTHERWISE...MONDAY LOOKING TO BE QUITE
WARM WITH ABOVE NORMAL HIGHS REACHING INTO THE LOWER TO MID 80S
FOR THE AREA WITH SOUTH GUSTS OF 30 TO 35 MPH POSSIBLE IN THE
AFTERNOON. MODELS ARE IN GENERAL AGREEMENT IN OCCLUDING SYSTEM
MONDAY NIGHT INTO EARLY TUESDAY WITH INITIALLY BETTER UPPER
DYNAMICS/LOW LEVEL CONVG MONDAY AFTERNOON/EARLY EVENING SETTING UP
ACROSS PORTIONS OF IOWA/SOUTHERN MINNESOTA. AT THIS TIME...STILL
FEEL BETTER CONVECTIVE CHANCES WILL BE GENERALLY WEST OF MS
RIVER...ALTHOUGH WILL MAINTAIN SLIGHT CHANCE POPS FOR THUNDER FROM
WEST TO EAST MONDAY NIGHT.

SYSTEM WILL SLOWLY FILL TUESDAY AS DRY LOW/MID LEVEL AIR WORKS
INTO THE AREA. THERE MAY BE SOME ISOLD SHOWERS ALONG THE FRONT
EARLY TUESDAY ACROSS SOUTHEASTERN PORTIONS OF THE AREA...BUT
OVERWHELMING DRY AIR ADVECTION ACROSS THE AREA SHOULD RESULT IN
DRY AND VERY WINDY CONDITIONS FOR TUES AFTERNOON. COLD ADVECTION
TUESDAY AFTERNOON WILL ALLOW FOR MORE SUBSTANTIAL MIXED LAYER
DEPTHS AND EVEN SOME CONCERN FOR NUDGING UP AGAINST WIND ADVISORY
CRITERIA AND WILL INCLUDE MENTION OF THESE EXPECTED VERY WINDY
CONDITIONS IN THIS MORNINGS HWO. TEMPS RATHER TRICKY ON TUESDAY
WITH COLD ADVECTION FIGHTING THE EFFECTS OF DEEPER MIXING. MAY BE
A BIT WARM WITH HIGHS TUESDAY RANGING FROM MID 70S FAR NORTH
CENTRAL ILLINOIS TO LOWER 80S FAR SOUTHEAST...BUT THIS DOES APPEAR
TO BE A COMMON SETUP WHEN THE EFFECTS OF SUBSIDENCE/MIXING DO
ALLOW FOR WARMER THAN EXPECTED TEMPS...SO HAVE NOT CHANGED THESE
HIGHS MUCH AT THIS POINT WITH STILL SOME SUBTLE MODEL DIFFERENCES
IN TIMING THIS COLD ADVECTION.

WEATHER TO FINALLY QUIET DOWN TUESDAY NIGHT INTO WEDNESDAY AS NEXT
SFC HIGH SLIDES INTO THE REGION. LOW LEVEL FRONT NOT EXPECTED TO BE
TOO FAR SOUTH OF THE AREA...ALTHOUGH NOT EXPECTING THIS LOW LEVEL
BAROCLINIC ZONE TO BE ACTIVE WITH ANY PRECIP DUE TO LIMITED
MOISTURE. NEW MEDIUM RANGE MODELS STILL SUPPORT THE GOING EXTENDED
FORECAST OF CHANCES OF THUNDER LATE THURSDAY/FRIDAY WITH RENEWED
THETA-E ADVECTION IN ADVANCE OF NEXT SIGNIFICANT UPPER TROUGH
WORKING THROUGH NWRN CONUS. THIS PATTERN SHOULD ALSO ALLOW MUCH OF
THE AREA TO POTENTIALLY WARM BACK INTO THE LOWER 80S TOWARD THE END
OF THE WEEK.

&&

.FIRE WEATHER...
330 AM CDT

SFC PRESSURE GRADIENT WILL STRENGTHEN ON MONDAY AS STRONG SFC LOW
MOVES INTO SOUTHERN MINNESOTA. STILL SOME UNCERTAINTY REMAINS AS
TO MIXING HEIGHTS MONDAY AFTERNOON AND EXACTLY HOW MUCH LOW LEVEL
DRY AIR CAN MIX DOWN TO THE SURFACE. FORECASTED HIGHS INTO THE
LOWER TO MID 80S COMBINED WITH DEW PTS LIKELY MIXING OUT TO AROUND
50 WOULD SUPPORT MIN AFTERNOON RELATIVE HUMIDITIES AROUND 30
PERCENT. WHILE WIND GUSTS SHOULD BE UP AROUND 30 MPH MONDAY
AFTERNOON...ENOUGH UNCERTAINTY EXISTS WITH REGARDS TO MIXING AND
FUEL MOISTURES TO HOLD OFF ON ANY FIRE WEATHER HEADLINES AT THIS
TIME.

TUESDAY IS SHAPING UP AS ANOTHER DAY OF POTENTIAL FIRE WEATHER
CONCERN AS CONFIDENCE IN DEEPER MIXED LAYER IS HIGHER ALONG WITH
POTENTIAL OF SOME SOUTHWEST WIND GUSTS TO 40 TO 45 MPH. IN
CONTRAST TO MONDAY THE MAIN ELEMENT OF UNCERTAINTY WITH HOW LOW
AFTERNOON RELATIVE HUMIDITIES CAN REACH IS JUST HOW HIGH THE
TEMPERATURE WILL CLIMB. AT THIS TIME...HAVE FORECASTED MIN
AFTERNOON RELATIVE HUMIDITIES IN THE 30 TO 35 PERCENT RANGE BUT
THIS WILL NEED TO BE MONITORED FOR ANY CHANGES TO FUTURE
FORECASTS. ALSO IF FRONTAL PASSAGE DOES COME THROUGH DRY MONDAY
NIGHT INTO TUESDAY...FUEL MOISTURES WILL BE SOMEWHAT LOWER WHICH
WOULD INCREASE FIRE WEATHER RISK FOR TUESDAY.

MARSILI

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 06Z...

NONE.

IZZI

//DISCUSSION...UPDATED 06Z...

SKC WITH LIGHT WINDS OVERNIGHT. SOUTH TO SOUTHWEST WINDS DEVELOP
BY LATE MORNING SUNDAY WITH AN INCREASE IN MID LEVEL CLOUDS
EXPECTED IN ADVANCE OF A DEVELOPING WEAK SHORTWAVE SUNDAY
AFTERNOON. DEEPENING LOW PRESSURE OVER THE PLAINS SUNDAY NIGHT
SHOULD RESULT IN STRONG LOW LEVEL JET SUNDAY NIGHT WITH FORECAST
SOUNDINGS SUGGESTING A SHARP NEAR SFC INVERSION FAVORABLE FOR
LLWS. LOW LEVEL MOISTURE LOOKS TOO SCANT FOR PRECIP WITH JUST A
REMOTE CHANCE OF A SPRINKLE FROM THE MID LEVEL DECK SUN EVENING.

IZZI

//ORD AND MDW CONFIDENCE...UPDATED 06Z...

HIGH CONFIDENCE IN ALL ASPECTS OF THE TAFS.

IZZI

//OUTLOOK FOR ORD/MDW FOR 12Z MONDAY-12Z SATURDAY...UPDATED 06Z...

MONDAY...VFR. SOUTH WIND GUSTS OVER 30KT POSSIBLE DURING DAYTIME.
TUESDAY...VFR. SOUTHWEST->WEST WIND GUSTS OVER 30KT DURING DAYTIME.
WEDNESDAY...VFR.
THURSDAY AND FRIDAY...SLIGHT CHANCE OF TSRA OTHERWISE VFR.

IZZI

&&

.MARINE...
330 AM CDT

STILL SEEING SOME ACCELERATION OF THE WINDS THIS MORNING OVER
EASTERN PORTIONS OF THE LAKE NEAR THE LAKE INSTABILITY INDUCED
CONVERGENCE BANDS. THOSE LOCALIZED WIND MAXIMA WILL FADE AFTER
SUNRISE WITH GRADIENT RELAXING AND WINDS BACKING IN ADVANCE OF THE
NEXT STORM SYSTEM.

MODEL GUIDANCE REMAINS IN EXCELLENT AGREEMENT ON TRACKING A DEEP LOW
FROM THE HIGH PLAINS THIS EVENING TO LAKE SUPERIOR BY TUESDAY
MORNING. VERY STRONG PRESSURE GRADIENT ASSOCIATED WITH THIS LARGE
AND RATHER INTENSE LOW SHOULD RESULT IN AN EXTENDED PERIOD OF HIGH
WINDS/WAVES. FORECAST SOUNDINGS FROM THE GFS/WRF-NAM BOTH CONTINUE
TO SUGGEST SUFFICIENTLY STEEP LOW LEVEL LAPSE RATES MONDAY INTO
MONDAY EVENING TO TAP INTO THE GALE FORCE WINDS ALOFT...HOWEVER
STRONGLY SUSPECT THAT WATER TEMPS IN THE MODELS ARE TOO WARM AND DO
NOT ACCOUNT FOR THE RECENT UPWELLING THAT HAS OCCURRED. MODEL 2M
TEMPS ARE PROGGED TO GET INTO THE MID-UPPER 70S OVER THE LAKE AND
INTO THE 80S OVER LAND...WHICH BEING ADVECTED OVER TOP THE UPPER
60/NEAR 70F WATERS SHOULD RESULT IN A NOTICEABLY MORE STABLE MARINE
LAYER MONDAY INTO MONDAY EVENING. FOR THIS REASON HAVE UNDERCUT
MODEL WINDS AND PARTICULARLY GUSTS AND HELD SPEEDS JUST BELOW GALE
FORCE THRU MON EVENING.

LATER MONDAY NIGHT INTO TUESDAY AS OCCLUDED FRONT MOVE THROUGH
EXPECT COLD AIR ADVECTION TO STEEPEN UP THE LAPSE RATES AND ALLOW
WINDS TO REALLY RAMP UP OVER THE LAKE. WHILE LOW WILL BE IN A
WEAKENING PHASE TUESDAY...THAT WILL ACTUALLY ONLY WORK TO ENHANCE
THE PRESSURE RISES AS THE LOW PULLS OFF TO THE EAST. GIVEN
THIS...HAVE FOLLOWED MODEL GUIDANCE WHICH IS IN GOOD AGREEMENT ON
GALES DEVELOPING LATE MONDAY NIGHT AND LASTING UNTIL TUESDAY
EVENING. GIVEN THE STRONG MODEL CONSENSUS AND RUN-TO-RUN CONSISTENCY
HAVE GONE AHEAD AND HOISTED A GALE WATCH FOR THE OPEN LAKE FOR LATE
MON NIGHT INTO TUESDAY. GALE WATCH MAY WELL NEED TO BE EXPANDED INTO
THE NEARSHORE WATERS AS WELL...BUT THAT WILL BE A 5TH PERIOD EVENT
AND WITH SLIGHTLY LESSER CONFIDENCE THAN OVER THE OPEN LAKE WILL
PUNT THAT DECISION TO THE LATER SHIFTS.

IZZI

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...GALE WATCH...LMZ080-LMZ567-LMZ669-LMZ671-LMZ673-LMZ675-LMZ777-
     LMZ779-LMZ868-LMZ870-LMZ872-LMZ874-LMZ876-LMZ878...MIDNIGHT
     TUESDAY TO 9 PM TUESDAY.

     GALE WATCH...LMZ261-LMZ362-LMZ364-LMZ366-LMZ563-LMZ565...5 AM
     TUESDAY TO 9 PM TUESDAY.

&&

$$

000
FXUS63 KILX 050830
AFDILX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LINCOLN IL
330 AM CDT SUN SEP 5 2010

.DISCUSSION...
ISSUED 330 AM CDT SUN SEP 5 2010

00Z MODELS REMAIN IN FAIR AGREEMENT NEXT FEW DAYS THEN DIVERGE
LATER IN THE WEEK. MODELS CONTINUE TO SHOW STRONG LOW PRESSURE
PASSING WELL NORTH OF IL MON NIGHT/TUE WITH WEAKENING FRONT MOVING
THROUGH CENTRAL/SE IL WITH BREEZY CONDITIONS AND LITTLE OR NO QPF
DUE TO VERY LIMITED MOISTURE. LEANED ON THE WARMER MAV HIGHS NEXT
FEW DAYS WHICH HAVE BETTER TRACK RECORD.

SHORT TERM...TODAY THROUGH TUESDAY NIGHT.

WEAK HIGH PRESSURE 1017 MB OVER THE OHIO AND MID MS VALLEYS
PROVIDING CLEAR SKIES AND CALME WINDS OVER CENTRAL/SE IL EARLY
THIS MORNING. COOL FALL LIKE TEMPS IN THE UPPER 40S AND LOWER 50S
AND COOLEST MORNING SINCE MAY 19TH.

ANOTHER NICE DAY AHEAD WITH PARTLY TO MOSTLY SUNNY SKIES AND
MILDER HIGHS IN THE UPPER 70S TO NEAR 80F. WEAK HIGH PRESSURE OVER
THE OHIO VALLEY TO DRIFT EAST INTO THE MID ATLANTIC STATES TONIGHT
WHILE LOW PRESSURE DEEPENS OVER NEBRASKA. STRONG UPPER LEVEL LOW
ALONG THE ALBERTA AND SASKETCHEWAN PROVINCE LINE DIGS INTO THE
NORTHERN PLAINS MON AND BRINGS DEEP LOW PRESSURE INTO THE UPPER MS
VALLEY. TIGHTENING PRESSURE GRADIENT OVER IL MON WITH INCREASING
SSW WINDS BRINGING WARMER AIR WITH HIGHS IN THE MID 80S CENTRAL IL
AND UPPER 80S SE IL.

MODELS HAVE TRENDED QUICKER WITH FRONT MOVING THROUGH IL OVERNIGHT
MON NIGHT AND TUE MORNING AND GENERALLY COMES THROUGH DRY WITH
LIMITED MOISTURE TO WORK WITH AND UPPER LEVEL DYNAMICS PASSING
WELL NORTH OF CENTRAL IL OVER THE UPPER GREAT LAKES. HAVE JUST
SLIGHT CHANCE AT BEST OVER THE IL RIVER VALLEY AFTER MIDNIGHT MON
NIGHT AND OVER REST OF AREA TUE. WITH FASTER MOVEMENT OF FRONT
COOLED HIGHS A BIT ON TUE WITH AROUND 80F OVER THE IL RIVER VALLEY
AND NEAR 90F AT LAWRENCEVILLE. STILL BREEZY TUE WITH STRONG LOW
PRESSURE PASSING JUST NORTH OF MI.

LONG TERM...WEDNESDAY THROUGH SATURDAY.

EXTENDED MODELS BUILD UPPER LEVEL RIDGE INTO THE MS VALLEY WED-FRI
WHICH SHOULD ALLOW TEMPS TO MODIFY AGAIN DURING THIS TIME FRAME
WITH MID TO UPPER 80S FRI/SAT AND LAWRENCEVILLE NEAR 90F. MOISTURE
FROM THE WESTERN GULF LIFTING NORTHWARD INTO THE OZARKS WED AND
POSSIBLY INTO CENTRAL/SOUTHERN IL THU. CONTINUED TO HAVE 20-30%
CHANCES SW AREAS WED AND ACROSS AREA THU.

HUETTL

&&

.AVIATION...
ISSUED 1139 PM CDT SAT SEP 4 2010...FOR THE 06Z TAFS

WAA PATTERN IS BECOMING EVIDENT ACROSS THE PLAINS BASED ON THE
SATELLITE IMAGES. WE WILL MOST LIKELY SEE SOME AC CLOUDS BY MID
MORNING...ALONG WITH INCREASING SOUTHERLY WINDS ON THE SOUTH SIDE
OF A DEVELOPING WARM FRONT. WILL PUT SOME GUSTS TO 20 KT FOR
PIA/SPI...CLOSER TO THE TIGHTER PRESSURE GRADIENT.

ANY CIGS WILL BE VFR AT 12K FT OR HIGHER. PATCHY LIGHT FOG MAY
DEVELOP IN LOW LYING AREAS...BUT WE DO NOT EXPECT ANY TAF SITES TO
BE AFFECTED.

SHIMON
&&

.ILX WATCHES/WARNINGS/ADVISORIES...
NONE.
&&

$$

000
FXUS63 KLOT 050534
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
1234 AM CDT SUN SEP 5 2010

.DISCUSSION...
244 PM CDT

UNSEASONABLY COOL TEMPERATURES AND BREEZY CONDITIONS OCCURRED TODAY
AS A LOW PRESSURE SYSTEM DRIFTED SLOWLY EAST OVER WESTERN QUEBEC BUT
DO EXPECT WARMER WEATHER CONDITIONS TO FINISH OUT THIS HOLIDAY
WEEKEND. A TIGHT PRESSURE GRADIENT WILL CONTINUE TO RELAX OVER THE
NEXT 24 HOURS AS A RIDGE OF HIGH PRESSURE BEGINS TO MOVE INTO THE
UPPER MIDWEST. THIS WILL CAUSE WINDS TO WEAKEN AND EVENTUALLY SHIFT
TO MORE SOUTHERLY ON SUNDAY AS THE RIDGE AXIS SHIFTS TO THE EAST OF
THE FORECAST AREA. THIS WILL ALLOW WARMER AIR TO ENTER THE
REGION...THUS CONTINUE TO CALL FOR AN 8-10F WARMING TREND EACH DAY
FOR THE NEXT COUPLE DAYS. H85 TEMPS IN THE LOW SINGLE DIGITS TODAY
WILL GRADUALLY WARM TO NEAR 20C BY MONDAY AFTERNOON AS A LOW
PRESSURE SYSTEM DEVELOPS OVER THE NORTHERN PLAINS AND SOUTHWESTERLY
FLOW INCREASES.

A WEAK WARM FRONT PASSES THROUGH SUNDAY NIGHT INTO MONDAY
MORNING...HOWEVER DUE TO THE ALIGNMENT OF THE RIDGE AXIS WHICH
EXTENDS SOUTHWEST INTO LOUISIANA...MOISTURE AVAILABILITY WILL BE A
LIMITING FACTOR FOR ANY WIDESPREAD PRECIPITATION. MODELS INDICATE A
DRY FRONTAL PASSAGE AND PRECIP IS EXPECTED TO OCCUR FURTHER NORTH
WHERE MORE FAVORABLE ISENTROPIC LIFT IS OCCURRING. AS THE LOW LIFTS
NORTH INTO CANADA...A TRAILING COLD FRONT IS THEN EXPECTED TO PUSH
THROUGH THE REGION TUESDAY. MODELS SOUNDINGS SHOW WEAK MID LEVEL LAPS
RATES...AND ELEVATED WARM LAYER. IN ADDITION...WINDS BEHIND FRONT
NEVER REALLY GAIN ANY NORTHERLY COMPONENT...AND WITH RIDGE AXIS
SOUTH OF THE AREA STILL STRETCHING AS FAR WEST AS TEXAS...DONT SEE
MUCH IN TERMS OF MOISTURE AVAILABILITY. ALL THINGS
CONSIDERED...SYSTEM DOES NOT LOOK TERRIBLY IMPRESSIVE SO ONLY
CALLING FOR SLIGHT CHANCE PRECIPITATION ALONG THE FRONT. AMPLIFIED
UPPER RIDGE THEN BUILDS OVERHEAD FOR THE MIDDLE OF NEXT WEEK WITH
THE NEXT SIGNIFICANT SYSTEM EXPECTED FRIDAY.

BMD

&&

.FIRE WEATHER...
330 AM CDT

ON MONDAY...SOUTH WINDS ARE EXPECTED TO INCREASE INTO THE 15 TO 25
MPH RANGE WITH SOME GUSTS TO 30 MPH OR SLIGHTLY HIGHER. THERE IS A
POSSIBILITY THAT SOME DRIER LOW LEVEL AIR MAY MIX DOWN TO THE
SURFACE WHICH WOULD RESULT IN MINIMUM AFTERNOON RELATIVE
HUMIDITIES AROUND OR LESS THAN 30 PERCENT. CONFIDENCE IN MEETING
RED FLAG CONDITIONS IS LOW AT THIS POINT GIVEN UNCERTAINTY AS TO
HOW MUCH OF THIS LOW LEVEL DRY AIR WILL MIX TO THE SURFACE...AND
ALSO 10 HR FUEL MOISTURES ARE STILL RUNNING ON THE HIGH SIDE
ACROSS THE AREA.

MARSILI

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 06Z...

NONE.

IZZI

//DISCUSSION...UPDATED 06Z...

SKC WITH LIGHT WINDS OVERNIGHT. SOUTH TO SOUTHWEST WINDS DEVELOP
BY LATE MORNING SUNDAY WITH AN INCREASE IN MID LEVEL CLOUDS
EXPECTED IN ADVANCE OF A DEVELOPING WEAK SHORTWAVE SUNDAY
AFTERNOON. DEEPENING LOW PRESSURE OVER THE PLAINS SUNDAY NIGHT
SHOULD RESULT IN STRONG LOW LEVEL JET SUNDAY NIGHT WITH FORECAST
SOUNDINGS SUGGESTING A SHARP NEAR SFC INVERSION FAVORABLE FOR
LLWS. LOW LEVEL MOISTURE LOOKS TOO SCANT FOR PRECIP WITH JUST A
REMOTE CHANCE OF A SPRINKLE FROM THE MID LEVEL DECK SUN EVENING.

IZZI

//ORD AND MDW CONFIDENCE...UPDATED 06Z...

HIGH CONFIDENCE IN ALL ASPECTS OF THE TAFS.

IZZI

//OUTLOOK FOR ORD/MDW FOR 12Z MONDAY-12Z SATURDAY...UPDATED 06Z...

MONDAY...VFR. SOUTH WIND GUSTS OVER 30KT POSSIBLE DURING DAYTIME.
TUESDAY...VFR. SOUTHWEST->WEST WIND GUSTS OVER 30KT DURING DAYTIME.
WEDNESDAY...VFR.
THURSDAY AND FRIDAY...SLIGHT CHANCE OF TSRA OTHERWISE VFR.

IZZI

&&

.MARINE...
151 PM CDT

THE LOW IN NORTHWEST QUEBEC WILL REMAIN IN NORTHWEST QUEBEC
THROUGH SUNDAY MORNING. THEN THE LOW MAY MOVE TO JUST WEST OF
JAMES BAY AFTER MIDNIGHT SUNDAY NIGHT. THE WIND WILL BE NORTHWEST
UNTIL VERY EARLY SUNDAY MORNING. A STRONG LOW WILL DEVELOP IN
WESTERN NEBRASKA SUNDAY AFTERNOON. THIS LOW WILL CAUSE THE WIND TO
BECOME SOUTH OVER LAKE MICHIGAN SUNDAY. THE SOUTHERN HALF OF THE
LAKE WILL HAVE A SOUTH WIND BY SUNDAY AFTERNOON AND THE NORTHERN
HALF WILL HAVE A SOUTH WIND BY SUNDAY EVENING. THE WIND SPEED WILL
BE 10 TO 15 KNOTS. THE WAVES WILL NOT BE AS LARGE AS THEY WERE
THIS SATURDAY MORNING.

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY...INDIANA NEARSHORE WATERS UNTIL 4 AM SUNDAY.

&&

$$

000
FXUS63 KILX 050439
AFDILX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LINCOLN IL
1139 PM CDT SAT SEP 4 2010

.DISCUSSION...
ISSUED 847 PM CDT SAT SEP 4 2010

QUIET WEATHER IS EXPECTED THE REST OF THE NIGHT AS LIGHT WINDS
DEVELOP UNDER THE SURFACE RIDGE AXIS. SKIES WILL REMAIN MOSTLY
CLEAR...DESPITE INCREASING WAA FLOWS ALOFT TOWARD MORNING.
RADIATIONAL COOLING WILL BE MAXIMIZED OVERNIGHT...WITH SOME OF THE
COOLEST LOW TEMPS WE HAVE SEEN IN QUITE A WHILE. LOW TEMPS WILL
LIKELY DIP INTO THE MID TO UPPER 40S.

THE FORECAST GRIDS HAVE A GOOD HANDLE ON THE EXPECTED
CONDITIONS...SO NO FORMAL UPDATE WILL BE NEEDED THIS EVENING.

SHIMON

&&

.AVIATION...
ISSUED 1139 PM CDT SAT SEP 4 2010...FOR THE 06Z TAFS

WAA PATTERN IS BECOMING EVIDENT ACROSS THE PLAINS BASED ON THE
SATELLITE IMAGES. WE WILL MOST LIKELY SEE SOME AC CLOUDS BY MID
MORNING...ALONG WITH INCREASING SOUTHERLY WINDS ON THE SOUTH SIDE
OF A DEVELOPING WARM FRONT. WILL PUT SOME GUSTS TO 20 KT FOR
PIA/SPI...CLOSER TO THE TIGHTER PRESSURE GRADIENT.

ANY CIGS WILL BE VFR AT 12K FT OR HIGHER. PATCHY LIGHT FOG MAY
DEVELOP IN LOW LYING AREAS...BUT WE DO NOT EXPECT ANY TAF SITES TO
BE AFFECTED.

SHIMON
&&

.PREV DISCUSSION...
ISSUED 300 PM CDT SAT SEP 4 2010

SHORT TERM...TONIGHT THROUGH TUESDAY...
SURFACE HIGH PRESSURE FROM N TX INTO IA WILL MOVE EWD ACROSS THE
AREA TONIGHT. LIGHT WLY WINDS WILL BECOME SLY ON SUN AND BEGIN A
WARMING TREND THAT WILL CONTINUE INTO TUE. MODELS ARE PRODUCING SOME
MID LEVEL CLOUDS LATE TONIGHT ON THE LEADING EDGE OF THE MID/UPPER
LEVEL RIDGE THAT IS NOW COMING EWD INTO THE PLAINS. THESE SHOULD
MOVE N OF THE AREA DURING THE AFTERNOON...AND IT APPEARS THAT THE
BETTER CHANCES FOR SHOWERS WILL BE TO THE N OF CENTRAL IL SUN
AFTN/EVE WHERE WIND FIELDS WILL BE A BIT STRONGER AND TEMPERATURES
ALOFT COOLER. WARMER 850 MB TEMPERATURES ON SUN WILL MIX DOWN AND
RESULT IN MAXES A COUPLE OF CATEGORIES WARMER THAN TODAY...WITH MOST
AREAS SEEING HIGHS 75-80.

NEXT POTENTIAL WEATHER MAKER WILL BE A STRONG UPPER LOW THAT IS NOW
MOVING SEWD TOWARD THE PACIFIC NORTHWEST. BY LATE MON...THIS FEATURE
WILL BE COMING INTO THE PLAINS AND BY DAWN TUE MORN...THE ASSOCIATED
SURFACE LOW WILL BE NEAR THE WRN GREAT LAKES WITH A COLD FRONT
EXTENDING SWD INTO NWRN IL. MOISTURE RETURN AHEAD OF THE FRONT WILL
BE RATHER MEAGER INITIALLY...BUT MAY BE SUFFICIENT FOR SOME SHOWERS
ALONG AND IMMEDIATELY BEHIND THE FRONT. WILL KEEP SLIGHT CHANCE POPS
GOING FOR THE NW AFTER MIDNIGHT MON NIGHT...WITH A LITTLE HIGHER
POPS ON TUESDAY WITH FRONTAL PASSAGE. ANY PRECIPITATION THAT DOES
OCCUR SHOULD BE FAIRLY LIGHT GIVEN THE LIMITED AVAILABLE MOISTURE.
AHEAD OF THE FRONT...TEMPERATURES WILL CONTINUE THEIR WARMING TREND
WITH HIGHS ON TUE FROM THE MID 80S TO LOWER 90S IN THE CENTRAL AND
SE.

LONG TERM...WEDNESDAY THROUGH SUNDAY...
HIGH PRESSURE AND DRIER AIR BEHIND THE FRONT SHOULD KEEP WED MAINLY
DRY AND A BIT COOLER. THE MODELS HAVE BEEN DIFFERING ON HOW STRONGLY
THE SURFACE RIDGE WILL BUILD SWD INTO THE MIDWEST AND WHETHER THERE
WILL BE ANY LEFT-OVER SHOWERS IN SRN IL. BOTH THE GFS AND ECMWF
MODELS ARE PRETTY CLOSE IN SLOWING THE COLD FRONT IN SRN IL BUT THE
ECMWF PLACES POST-FRONTAL QPF FURTHER N INTO IL THAN THE GFS. THIS
IS ABOUT THE OPPOSITE OF WHAT EACH MODEL WAS INDICATING 12 HOURS
AGO...WHICH ADDS TO THE UNCERTAINTY. FOR NOW WILL KEEP SLIGHT CHANCE
POPS IN THE SE FOR WED.

THE STRENGTH/DEPTH OF THE WED SURFACE HIGH WILL ALSO HAVE AN IMPACT
ON WHEN THE NEXT CHANCE OF RAIN WILL BE. WITH THE UPPER PATTERN
BEING FAIRLY AMPLIFIED AS DEEP TROUGHS SET UP OVER BOTH COASTS...IT
SEEMS MORE PROBABLE THAT THE GFS MAY BE MORE REALISTIC IN PUSHING
THE HIGH PRESSURE FURTHER SOUTH THAN THE ECMWF. THUS WILL KEEP POPS
OUT OF WED NIGHT/THU. AFTER THAT...THE UPPER FLOW BECOMES SWLY AS
THE WRN UPPER TROUGH SWINGS NEWD INTO CANADA. THE STALLED FRONT TO
THE SOUTH WILL BE PULLED NORTHWARD AND POSSIBLY PRODUCE SOME
CONVECTION LATE THU NIGHT AND INTO FRI...FOLLOWED BY THE COLD FRONT
ON SUN. SINCE THE EXTENDED RANGE MODEL ENSEMBLES ARE SHOWING QUITE A
BIT OF SPREAD REGARDING THIS AS WELL AS THE PRECEDING MID-WEEK
SYSTEM...WILL KEEP POPS BELOW MENTIONABLE LEVELS FOR NOW.

04

&&

.ILX WATCHES/WARNINGS/ADVISORIES...
NONE.
&&

$$

000
FXUS63 KLOT 050308
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
1008 PM CDT SAT SEP 4 2010

.DISCUSSION...
244 PM CDT

UNSEASONABLY COOL TEMPERATURES AND BREEZY CONDITIONS OCCURRED TODAY
AS A LOW PRESSURE SYSTEM DRIFTED SLOWLY EAST OVER WESTERN QUEBEC BUT
DO EXPECT WARMER WEATHER CONDITIONS TO FINISH OUT THIS HOLIDAY
WEEKEND. A TIGHT PRESSURE GRADIENT WILL CONTINUE TO RELAX OVER THE
NEXT 24 HOURS AS A RIDGE OF HIGH PRESSURE BEGINS TO MOVE INTO THE
UPPER MIDWEST. THIS WILL CAUSE WINDS TO WEAKEN AND EVENTUALLY SHIFT
TO MORE SOUTHERLY ON SUNDAY AS THE RIDGE AXIS SHIFTS TO THE EAST OF
THE FORECAST AREA. THIS WILL ALLOW WARMER AIR TO ENTER THE
REGION...THUS CONTINUE TO CALL FOR AN 8-10F WARMING TREND EACH DAY
FOR THE NEXT COUPLE DAYS. H85 TEMPS IN THE LOW SINGLE DIGITS TODAY
WILL GRADUALLY WARM TO NEAR 20C BY MONDAY AFTERNOON AS A LOW
PRESSURE SYSTEM DEVELOPS OVER THE NORTHERN PLAINS AND SOUTHWESTERLY
FLOW INCREASES.

A WEAK WARM FRONT PASSES THROUGH SUNDAY NIGHT INTO MONDAY
MORNING...HOWEVER DUE TO THE ALIGNMENT OF THE RIDGE AXIS WHICH
EXTENDS SOUTHWEST INTO LOUISIANA...MOISTURE AVAILABILITY WILL BE A
LIMITING FACTOR FOR ANY WIDESPREAD PRECIPITATION. MODELS INDICATE A
DRY FRONTAL PASSAGE AND PRECIP IS EXPECTED TO OCCUR FURTHER NORTH
WHERE MORE FAVORABLE ISENTROPIC LIFT IS OCCURRING. AS THE LOW LIFTS
NORTH INTO CANADA...A TRAILING COLD FRONT IS THEN EXPECTED TO PUSH
THROUGH THE REGION TUESDAY. MODELS SOUNDINGS SHOW WEAK MID LEVEL LAPS
RATES...AND ELEVATED WARM LAYER. IN ADDITION...WINDS BEHIND FRONT
NEVER REALLY GAIN ANY NORTHERLY COMPONENT...AND WITH RIDGE AXIS
SOUTH OF THE AREA STILL STRETCHING AS FAR WEST AS TEXAS...DONT SEE
MUCH IN TERMS OF MOISTURE AVAILABILITY. ALL THINGS
CONSIDERED...SYSTEM DOES NOT LOOK TERRIBLY IMPRESSIVE SO ONLY
CALLING FOR SLIGHT CHANCE PRECIPITATION ALONG THE FRONT. AMPLIFIED
UPPER RIDGE THEN BUILDS OVERHEAD FOR THE MIDDLE OF NEXT WEEK WITH
THE NEXT SIGNIFICANT SYSTEM EXPECTED FRIDAY.

BMD

&&

.FIRE WEATHER...
330 AM CDT

ON MONDAY...SOUTH WINDS ARE EXPECTED TO INCREASE INTO THE 15 TO 25
MPH RANGE WITH SOME GUSTS TO 30 MPH OR SLIGHTLY HIGHER. THERE IS A
POSSIBILITY THAT SOME DRIER LOW LEVEL AIR MAY MIX DOWN TO THE
SURFACE WHICH WOULD RESULT IN MINIMUM AFTERNOON RELATIVE
HUMIDITIES AROUND OR LESS THAN 30 PERCENT. CONFIDENCE IN MEETING
RED FLAG CONDITIONS IS LOW AT THIS POINT GIVEN UNCERTAINTY AS TO
HOW MUCH OF THIS LOW LEVEL DRY AIR WILL MIX TO THE SURFACE...AND
ALSO 10 HR FUEL MOISTURES ARE STILL RUNNING ON THE HIGH SIDE
ACROSS THE AREA.

MARSILI

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 03Z...

WINDS WILL REMAIN LGT FROM W/NW. WINDS BECOME SW BY 15Z THEN GUSTY
SW WINDS TO 20KTS BY 18Z.

BEACHLER

//DISCUSSION...UPDATED 00Z...

VERY DRY AIR MASS CONTINUES TO HOVER OVER THE GREAT LAKES REGION
AND PROVIDE MINIMAL CLOUD COVER. HIGH PRESSURE WILL REMAIN
CENTERED SOUTH OF NORTHERN IL/NORTHWEST IN...AND SLOWLY DRIFT EAST
OVERNIGHT. SKIES WILL BECOME SKC BY 02-03Z AND REMAIN THRU
DAYBREAK SUN. WINDS WILL RAPIDLY DECOUPLE BY 02Z WITH NW WINDS
ARND 5-7KTS FOR MOST TERMINALS. THEN AS HIGH PRESSURE DRIFTS EAST
OVERNIGHT WINDS WILL BACK TO SOUTHWESTERLY ARND 12-15Z...THEN
GRADUALLY INCREASE. BY 18Z SW WINDS WILL GUST BTWN 15-20KTS THRU
00Z MON. THE ATMOS SHUD REMAIN RELATIVELY DRY...WITH MINIMAL
MOISTURE ADVECTING INTO NORTHERN IL/NORTHWEST IN SUN AFTN CLOUDS
SHUD REMAIN MINIMAL. SOME GUIDANCE MEMBERS ARE SUGGESTING LATE SUN
ADDTL CLOUDS/MOISTURE WILL ADVECT NE TWRDS NORTHERN IL...HOWEVER
THIS APPEARS TO BE MORE LIKELY AS CLOUDS. THUS PRECIP SHUD REMAIN
OUT OF AIRFIELDS THRU AT LEAST 00Z MON.

BEACHLER

//ORD AND MDW CONFIDENCE...UPDATED 03Z...

HIGH CONFIDENCE IN ALL FORECAST ELEMENTS.

BEACHLER

//OUTLOOK FOR ORD/MDW FOR 06Z MONDAY-12Z FRIDAY...UPDATED 18Z...

SUNDAY NIGHT...VFR.
MONDAY...VFR. CHC TSRA LATE.
TUESDAY...VFR. CHC SHRA/ISO TSRA W/PATCHY MVFR.
WEDNESDAY...VFR. CHC SHRA/ISO TSRA EARLY.
THURSDAY...VFR. CHC SHRA/ISO TSRA.
FRIDAY...VFR. CHC TSRA.

&&

.MARINE...
151 PM CDT

THE LOW IN NORTHWEST QUEBEC WILL REMAIN IN NORTHWEST QUEBEC
THROUGH SUNDAY MORNING. THEN THE LOW MAY MOVE TO JUST WEST OF
JAMES BAY AFTER MIDNIGHT SUNDAY NIGHT. THE WIND WILL BE NORTHWEST
UNTIL VERY EARLY SUNDAY MORNING. A STRONG LOW WILL DEVELOP IN
WESTERN NEBRASKA SUNDAY AFTERNOON. THIS LOW WILL CAUSE THE WIND TO
BECOME SOUTH OVER LAKE MICHIGAN SUNDAY. THE SOUTHERN HALF OF THE
LAKE WILL HAVE A SOUTH WIND BY SUNDAY AFTERNOON AND THE NORTHERN
HALF WILL HAVE A SOUTH WIND BY SUNDAY EVENING. THE WIND SPEED WILL
BE 10 TO 15 KNOTS. THE WAVES WILL NOT BE AS LARGE AS THEY WERE
THIS SATURDAY MORNING.

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY...INDIANA NEARSHORE WATERS UNTIL 4 AM SUNDAY.

&&

$$

000
FXUS63 KILX 050147
AFDILX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LINCOLN IL
847 PM CDT SAT SEP 4 2010

.DISCUSSION...
ISSUED 847 PM CDT SAT SEP 4 2010

QUIET WEATHER IS EXPECTED THE REST OF THE NIGHT AS LIGHT WINDS
DEVELOP UNDER THE SURFACE RIDGE AXIS. SKIES WILL REMAIN MOSTLY
CLEAR...DESPITE INCREASING WAA FLOWS ALOFT TOWARD MORNING.
RADIATIONAL COOLING WILL BE MAXIMIZED OVERNIGHT...WITH SOME OF THE
COOLEST LOW TEMPS WE HAVE SEEN IN QUITE A WHILE. LOW TEMPS WILL
LIKELY DIP INTO THE MID TO UPPER 40S.

THE FORECAST GRIDS HAVE A GOOD HANDLE ON THE EXPECTED
CONDITIONS...SO NO FORMAL UPDATE WILL BE NEEDED THIS EVENING.

SHIMON
&&

.AVIATION...
ISSUED 655 PM CDT SAT SEP 4 2010...FOR THE 00Z TAFS

NO MAJOR CONCERNS FOR AVIATION OVER THE NEXT 24 HOURS. VFR
CONDITIONS ARE EXPECTED.

A CHANGE IN WIND DIRECTION WILL BE THE
PRIMARY CONCERN. NORTHWEST WINDS THIS EVENING WILL BECOME
SOUTHERLY TOMORROW MORNING...AS WAA FLOWS DEVELOP ALOFT AND
TRANSLATE TO THE SURFACE. SOME GUSTS TO 15-16KT ARE EXPECTED
TOMORROW IN OUR WESTERN AREAS.

WAA MID CLOUDS WILL BEGIN TO OVERSPREAD THE CWA FROM THE WEST
AFTER MIDNIGHT...BUT ANY CLOUD CIGS WILL BE VFR.

SHIMON
&&

.PREV DISCUSSION...
ISSUED 300 PM CDT SAT SEP 4 2010

SHORT TERM...TONIGHT THROUGH TUESDAY...
SURFACE HIGH PRESSURE FROM N TX INTO IA WILL MOVE EWD ACROSS THE
AREA TONIGHT. LIGHT WLY WINDS WILL BECOME SLY ON SUN AND BEGIN A
WARMING TREND THAT WILL CONTINUE INTO TUE. MODELS ARE PRODUCING SOME
MID LEVEL CLOUDS LATE TONIGHT ON THE LEADING EDGE OF THE MID/UPPER
LEVEL RIDGE THAT IS NOW COMING EWD INTO THE PLAINS. THESE SHOULD
MOVE N OF THE AREA DURING THE AFTERNOON...AND IT APPEARS THAT THE
BETTER CHANCES FOR SHOWERS WILL BE TO THE N OF CENTRAL IL SUN
AFTN/EVE WHERE WIND FIELDS WILL BE A BIT STRONGER AND TEMPERATURES
ALOFT COOLER. WARMER 850 MB TEMPERATURES ON SUN WILL MIX DOWN AND
RESULT IN MAXES A COUPLE OF CATEGORIES WARMER THAN TODAY...WITH MOST
AREAS SEEING HIGHS 75-80.

NEXT POTENTIAL WEATHER MAKER WILL BE A STRONG UPPER LOW THAT IS NOW
MOVING SEWD TOWARD THE PACIFIC NORTHWEST. BY LATE MON...THIS FEATURE
WILL BE COMING INTO THE PLAINS AND BY DAWN TUE MORN...THE ASSOCIATED
SURFACE LOW WILL BE NEAR THE WRN GREAT LAKES WITH A COLD FRONT
EXTENDING SWD INTO NWRN IL. MOISTURE RETURN AHEAD OF THE FRONT WILL
BE RATHER MEAGER INITIALLY...BUT MAY BE SUFFICIENT FOR SOME SHOWERS
ALONG AND IMMEDIATELY BEHIND THE FRONT. WILL KEEP SLIGHT CHANCE POPS
GOING FOR THE NW AFTER MIDNIGHT MON NIGHT...WITH A LITTLE HIGHER
POPS ON TUESDAY WITH FRONTAL PASSAGE. ANY PRECIPITATION THAT DOES
OCCUR SHOULD BE FAIRLY LIGHT GIVEN THE LIMITED AVAILABLE MOISTURE.
AHEAD OF THE FRONT...TEMPERATURES WILL CONTINUE THEIR WARMING TREND
WITH HIGHS ON TUE FROM THE MID 80S TO LOWER 90S IN THE CENTRAL AND
SE.

LONG TERM...WEDNESDAY THROUGH SUNDAY...
HIGH PRESSURE AND DRIER AIR BEHIND THE FRONT SHOULD KEEP WED MAINLY
DRY AND A BIT COOLER. THE MODELS HAVE BEEN DIFFERING ON HOW STRONGLY
THE SURFACE RIDGE WILL BUILD SWD INTO THE MIDWEST AND WHETHER THERE
WILL BE ANY LEFT-OVER SHOWERS IN SRN IL. BOTH THE GFS AND ECMWF
MODELS ARE PRETTY CLOSE IN SLOWING THE COLD FRONT IN SRN IL BUT THE
ECMWF PLACES POST-FRONTAL QPF FURTHER N INTO IL THAN THE GFS. THIS
IS ABOUT THE OPPOSITE OF WHAT EACH MODEL WAS INDICATING 12 HOURS
AGO...WHICH ADDS TO THE UNCERTAINTY. FOR NOW WILL KEEP SLIGHT CHANCE
POPS IN THE SE FOR WED.

THE STRENGTH/DEPTH OF THE WED SURFACE HIGH WILL ALSO HAVE AN IMPACT
ON WHEN THE NEXT CHANCE OF RAIN WILL BE. WITH THE UPPER PATTERN
BEING FAIRLY AMPLIFIED AS DEEP TROUGHS SET UP OVER BOTH COASTS...IT
SEEMS MORE PROBABLE THAT THE GFS MAY BE MORE REALISTIC IN PUSHING
THE HIGH PRESSURE FURTHER SOUTH THAN THE ECMWF. THUS WILL KEEP POPS
OUT OF WED NIGHT/THU. AFTER THAT...THE UPPER FLOW BECOMES SWLY AS
THE WRN UPPER TROUGH SWINGS NEWD INTO CANADA. THE STALLED FRONT TO
THE SOUTH WILL BE PULLED NORTHWARD AND POSSIBLY PRODUCE SOME
CONVECTION LATE THU NIGHT AND INTO FRI...FOLLOWED BY THE COLD FRONT
ON SUN. SINCE THE EXTENDED RANGE MODEL ENSEMBLES ARE SHOWING QUITE A
BIT OF SPREAD REGARDING THIS AS WELL AS THE PRECEDING MID-WEEK
SYSTEM...WILL KEEP POPS BELOW MENTIONABLE LEVELS FOR NOW.

04

&&

.ILX WATCHES/WARNINGS/ADVISORIES...
NONE.
&&

$$

000
FXUS63 KLOT 050010
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
710 PM CDT SAT SEP 4 2010

.DISCUSSION...
244 PM CDT

UNSEASONABLY COOL TEMPERATURES AND BREEZY CONDITIONS OCCURRED TODAY
AS A LOW PRESSURE SYSTEM DRIFTED SLOWLY EAST OVER WESTERN QUEBEC BUT
DO EXPECT WARMER WEATHER CONDITIONS TO FINISH OUT THIS HOLIDAY
WEEKEND. A TIGHT PRESSURE GRADIENT WILL CONTINUE TO RELAX OVER THE
NEXT 24 HOURS AS A RIDGE OF HIGH PRESSURE BEGINS TO MOVE INTO THE
UPPER MIDWEST. THIS WILL CAUSE WINDS TO WEAKEN AND EVENTUALLY SHIFT
TO MORE SOUTHERLY ON SUNDAY AS THE RIDGE AXIS SHIFTS TO THE EAST OF
THE FORECAST AREA. THIS WILL ALLOW WARMER AIR TO ENTER THE
REGION...THUS CONTINUE TO CALL FOR AN 8-10F WARMING TREND EACH DAY
FOR THE NEXT COUPLE DAYS. H85 TEMPS IN THE LOW SINGLE DIGITS TODAY
WILL GRADUALLY WARM TO NEAR 20C BY MONDAY AFTERNOON AS A LOW
PRESSURE SYSTEM DEVELOPS OVER THE NORTHERN PLAINS AND SOUTHWESTERLY
FLOW INCREASES.

A WEAK WARM FRONT PASSES THROUGH SUNDAY NIGHT INTO MONDAY
MORNING...HOWEVER DUE TO THE ALIGNMENT OF THE RIDGE AXIS WHICH
EXTENDS SOUTHWEST INTO LOUISIANA...MOISTURE AVAILABILITY WILL BE A
LIMITING FACTOR FOR ANY WIDESPREAD PRECIPITATION. MODELS INDICATE A
DRY FRONTAL PASSAGE AND PRECIP IS EXPECTED TO OCCUR FURTHER NORTH
WHERE MORE FAVORABLE ISENTROPIC LIFT IS OCCURRING. AS THE LOW LIFTS
NORTH INTO CANADA...A TRAILING COLD FRONT IS THEN EXPECTED TO PUSH
THROUGH THE REGION TUESDAY. MODELS SOUNDINGS SHOW WEAK MID LEVEL LAPS
RATES...AND ELEVATED WARM LAYER. IN ADDITION...WINDS BEHIND FRONT
NEVER REALLY GAIN ANY NORTHERLY COMPONENT...AND WITH RIDGE AXIS
SOUTH OF THE AREA STILL STRETCHING AS FAR WEST AS TEXAS...DONT SEE
MUCH IN TERMS OF MOISTURE AVAILABILITY. ALL THINGS
CONSIDERED...SYSTEM DOES NOT LOOK TERRIBLY IMPRESSIVE SO ONLY
CALLING FOR SLIGHT CHANCE PRECIPITATION ALONG THE FRONT. AMPLIFIED
UPPER RIDGE THEN BUILDS OVERHEAD FOR THE MIDDLE OF NEXT WEEK WITH
THE NEXT SIGNIFICANT SYSTEM EXPECTED FRIDAY.

BMD

&&

.FIRE WEATHER...
330 AM CDT

ON MONDAY...SOUTH WINDS ARE EXPECTED TO INCREASE INTO THE 15 TO 25
MPH RANGE WITH SOME GUSTS TO 30 MPH OR SLIGHTLY HIGHER. THERE IS A
POSSIBILITY THAT SOME DRIER LOW LEVEL AIR MAY MIX DOWN TO THE
SURFACE WHICH WOULD RESULT IN MINIMUM AFTERNOON RELATIVE
HUMIDITIES AROUND OR LESS THAN 30 PERCENT. CONFIDENCE IN MEETING
RED FLAG CONDITIONS IS LOW AT THIS POINT GIVEN UNCERTAINTY AS TO
HOW MUCH OF THIS LOW LEVEL DRY AIR WILL MIX TO THE SURFACE...AND
ALSO 10 HR FUEL MOISTURES ARE STILL RUNNING ON THE HIGH SIDE
ACROSS THE AREA.

MARSILI

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 00Z...

GUSTY WINDS DISSIPATE BY 02Z. WINDS BECOME SOUTHWEST AFT 15Z SUN
AND INCREASE TO 20KT GUSTS AFT 18Z SUN.

BEACHLER

//DISCUSSION...UPDATED 00Z...

VERY DRY AIR MASS CONTINUES TO HOVER OVER THE GREAT LAKES REGION
AND PROVIDE MINIMAL CLOUD COVER. HIGH PRESSURE WILL REMAIN
CENTERED SOUTH OF NORTHERN IL/NORTHWEST IN...AND SLOWLY DRIFT EAST
OVERNIGHT. SKIES WILL BECOME SKC BY 02-03Z AND REMAIN THRU
DAYBREAK SUN. WINDS WILL RAPIDLY DECOUPLE BY 02Z WITH NW WINDS
ARND 5-7KTS FOR MOST TERMINALS. THEN AS HIGH PRESSURE DRIFTS EAST
OVERNIGHT WINDS WILL BACK TO SOUTHWESTERLY ARND 12-15Z...THEN
GRADUALLY INCREASE. BY 18Z SW WINDS WILL GUST BTWN 15-20KTS THRU
00Z MON. THE ATMOS SHUD REMAIN RELATIVELY DRY...WITH MINIMAL
MOISTURE ADVECTING INTO NORTHERN IL/NORTHWEST IN SUN AFTN CLOUDS
SHUD REMAIN MINIMAL. SOME GUIDANCE MEMBERS ARE SUGGESTING LATE SUN
ADDTL CLOUDS/MOISTURE WILL ADVECT NE TWRDS NORTHERN IL...HOWEVER
THIS APPEARS TO BE MORE LIKELY AS CLOUDS. THUS PRECIP SHUD REMAIN
OUT OF AIRFIELDS THRU AT LEAST 00Z MON.

BEACHLER

//ORD AND MDW CONFIDENCE...UPDATED 00Z...

HIGH CONFIDENCE IN ALL FORECAST ELEMENTS.

BEACHLER

//OUTLOOK FOR ORD/MDW FOR 06Z MONDAY-12Z FRIDAY...UPDATED 18Z...

SUNDAY NIGHT...VFR.
MONDAY...VFR. CHC TSRA LATE.
TUESDAY...VFR. CHC SHRA/ISO TSRA W/PATCHY MVFR.
WEDNESDAY...VFR. CHC SHRA/ISO TSRA EARLY.
THURSDAY...VFR. CHC SHRA/ISO TSRA.
FRIDAY...VFR. CHC TSRA.

&&

.MARINE...
151 PM CDT

THE LOW IN NORTHWEST QUEBEC WILL REMAIN IN NORTHWEST QUEBEC
THROUGH SUNDAY MORNING. THEN THE LOW MAY MOVE TO JUST WEST OF
JAMES BAY AFTER MIDNIGHT SUNDAY NIGHT. THE WIND WILL BE NORTHWEST
UNTIL VERY EARLY SUNDAY MORNING. A STRONG LOW WILL DEVELOP IN
WESTERN NEBRASKA SUNDAY AFTERNOON. THIS LOW WILL CAUSE THE WIND TO
BECOME SOUTH OVER LAKE MICHIGAN SUNDAY. THE SOUTHERN HALF OF THE
LAKE WILL HAVE A SOUTH WIND BY SUNDAY AFTERNOON AND THE NORTHERN
HALF WILL HAVE A SOUTH WIND BY SUNDAY EVENING. THE WIND SPEED WILL
BE 10 TO 15 KNOTS. THE WAVES WILL NOT BE AS LARGE AS THEY WERE
THIS SATURDAY MORNING.

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY...INDIANA NEARSHORE WATERS UNTIL 4 AM SUNDAY.

     SMALL CRAFT ADVISORY...ILLINOIS NEARSHORE WATERS UNTIL 10 PM SATURDAY.

&&

$$

000
FXUS63 KILX 042355
AFDILX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LINCOLN IL
655 PM CDT SAT SEP 4 2010

.DISCUSSION...
ISSUED 300 PM CDT SAT SEP 4 2010

SHORT TERM...TONIGHT THROUGH TUESDAY...
SURFACE HIGH PRESSURE FROM N TX INTO IA WILL MOVE EWD ACROSS THE
AREA TONIGHT. LIGHT WLY WINDS WILL BECOME SLY ON SUN AND BEGIN A
WARMING TREND THAT WILL CONTINUE INTO TUE. MODELS ARE PRODUCING SOME
MID LEVEL CLOUDS LATE TONIGHT ON THE LEADING EDGE OF THE MID/UPPER
LEVEL RIDGE THAT IS NOW COMING EWD INTO THE PLAINS. THESE SHOULD
MOVE N OF THE AREA DURING THE AFTERNOON...AND IT APPEARS THAT THE
BETTER CHANCES FOR SHOWERS WILL BE TO THE N OF CENTRAL IL SUN
AFTN/EVE WHERE WIND FIELDS WILL BE A BIT STRONGER AND TEMPERATURES
ALOFT COOLER. WARMER 850 MB TEMPERATURES ON SUN WILL MIX DOWN AND
RESULT IN MAXES A COUPLE OF CATEGORIES WARMER THAN TODAY...WITH MOST
AREAS SEEING HIGHS 75-80.

NEXT POTENTIAL WEATHER MAKER WILL BE A STRONG UPPER LOW THAT IS NOW
MOVING SEWD TOWARD THE PACIFIC NORTHWEST. BY LATE MON...THIS FEATURE
WILL BE COMING INTO THE PLAINS AND BY DAWN TUE MORN...THE ASSOCIATED
SURFACE LOW WILL BE NEAR THE WRN GREAT LAKES WITH A COLD FRONT
EXTENDING SWD INTO NWRN IL. MOISTURE RETURN AHEAD OF THE FRONT WILL
BE RATHER MEAGER INITIALLY...BUT MAY BE SUFFICIENT FOR SOME SHOWERS
ALONG AND IMMEDIATELY BEHIND THE FRONT. WILL KEEP SLIGHT CHANCE POPS
GOING FOR THE NW AFTER MIDNIGHT MON NIGHT...WITH A LITTLE HIGHER
POPS ON TUESDAY WITH FRONTAL PASSAGE. ANY PRECIPITATION THAT DOES
OCCUR SHOULD BE FAIRLY LIGHT GIVEN THE LIMITED AVAILABLE MOISTURE.
AHEAD OF THE FRONT...TEMPERATURES WILL CONTINUE THEIR WARMING TREND
WITH HIGHS ON TUE FROM THE MID 80S TO LOWER 90S IN THE CENTRAL AND
SE.

LONG TERM...WEDNESDAY THROUGH SUNDAY...
HIGH PRESSURE AND DRIER AIR BEHIND THE FRONT SHOULD KEEP WED MAINLY
DRY AND A BIT COOLER. THE MODELS HAVE BEEN DIFFERING ON HOW STRONGLY
THE SURFACE RIDGE WILL BUILD SWD INTO THE MIDWEST AND WHETHER THERE
WILL BE ANY LEFT-OVER SHOWERS IN SRN IL. BOTH THE GFS AND ECMWF
MODELS ARE PRETTY CLOSE IN SLOWING THE COLD FRONT IN SRN IL BUT THE
ECMWF PLACES POST-FRONTAL QPF FURTHER N INTO IL THAN THE GFS. THIS
IS ABOUT THE OPPOSITE OF WHAT EACH MODEL WAS INDICATING 12 HOURS
AGO...WHICH ADDS TO THE UNCERTAINTY. FOR NOW WILL KEEP SLIGHT CHANCE
POPS IN THE SE FOR WED.

THE STRENGTH/DEPTH OF THE WED SURFACE HIGH WILL ALSO HAVE AN IMPACT
ON WHEN THE NEXT CHANCE OF RAIN WILL BE. WITH THE UPPER PATTERN
BEING FAIRLY AMPLIFIED AS DEEP TROUGHS SET UP OVER BOTH COASTS...IT
SEEMS MORE PROBABLE THAT THE GFS MAY BE MORE REALISTIC IN PUSHING
THE HIGH PRESSURE FURTHER SOUTH THAN THE ECMWF. THUS WILL KEEP POPS
OUT OF WED NIGHT/THU. AFTER THAT...THE UPPER FLOW BECOMES SWLY AS
THE WRN UPPER TROUGH SWINGS NEWD INTO CANADA. THE STALLED FRONT TO
THE SOUTH WILL BE PULLED NORTHWARD AND POSSIBLY PRODUCE SOME
CONVECTION LATE THU NIGHT AND INTO FRI...FOLLOWED BY THE COLD FRONT
ON SUN. SINCE THE EXTENDED RANGE MODEL ENSEMBLES ARE SHOWING QUITE A
BIT OF SPREAD REGARDING THIS AS WELL AS THE PRECEDING MID-WEEK
SYSTEM...WILL KEEP POPS BELOW MENTIONABLE LEVELS FOR NOW.

04

&&

.AVIATION...
ISSUED 655 PM CDT SAT SEP 4 2010...FOR THE 00Z TAFS

NO MAJOR CONCERNS FOR AVIATION OVER THE NEXT 24 HOURS. VFR
CONDITIONS ARE EXPECTED.

A CHANGE IN WIND DIRECTION WILL BE THE
PRIMARY CONCERN. NORTHWEST WINDS THIS EVENING WILL BECOME
SOUTHERLY TOMORROW MORNING...AS WAA FLOWS DEVELOP ALOFT AND
TRANSLATE TO THE SURFACE. SOME GUSTS TO 15-16KT ARE EXPECTED
TOMORROW IN OUR WESTERN AREAS.

WAA MID CLOUDS WILL BEGIN TO OVERSPREAD THE CWA FROM THE WEST
AFTER MIDNIGHT...BUT ANY CLOUD CIGS WILL BE VFR.

SHIMON
&&

.ILX WATCHES/WARNINGS/ADVISORIES...
NONE.
&&

$$

000
FXUS63 KLOT 042116
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
416 PM CDT SAT SEP 4 2010

.DISCUSSION...
244 PM CDT

UNSEASONABLY COOL TEMPERATURES AND BREEZY CONDITIONS OCCURRED TODAY
AS A LOW PRESSURE SYSTEM DRIFTED SLOWLY EAST OVER WESTERN QUEBEC BUT
DO EXPECT WARMER WEATHER CONDITIONS TO FINISH OUT THIS HOLIDAY
WEEKEND. A TIGHT PRESSURE GRADIENT WILL CONTINUE TO RELAX OVER THE
NEXT 24 HOURS AS A RIDGE OF HIGH PRESSURE BEGINS TO MOVE INTO THE
UPPER MIDWEST. THIS WILL CAUSE WINDS TO WEAKEN AND EVENTUALLY SHIFT
TO MORE SOUTHERLY ON SUNDAY AS THE RIDGE AXIS SHIFTS TO THE EAST OF
THE FORECAST AREA. THIS WILL ALLOW WARMER AIR TO ENTER THE
REGION...THUS CONTINUE TO CALL FOR AN 8-10F WARMING TREND EACH DAY
FOR THE NEXT COUPLE DAYS. H85 TEMPS IN THE LOW SINGLE DIGITS TODAY
WILL GRADUALLY WARM TO NEAR 20C BY MONDAY AFTERNOON AS A LOW
PRESSURE SYSTEM DEVELOPS OVER THE NORTHERN PLAINS AND SOUTHWESTERLY
FLOW INCREASES.

A WEAK WARM FRONT PASSES THROUGH SUNDAY NIGHT INTO MONDAY
MORNING...HOWEVER DUE TO THE ALIGNMENT OF THE RIDGE AXIS WHICH
EXTENDS SOUTHWEST INTO LOUISIANA...MOISTURE AVAILABILITY WILL BE A
LIMITING FACTOR FOR ANY WIDESPREAD PRECIPITATION. MODELS INDICATE A
DRY FRONTAL PASSAGE AND PRECIP IS EXPECTED TO OCCUR FURTHER NORTH
WHERE MORE FAVORABLE ISENTROPIC LIFT IS OCCURRING. AS THE LOW LIFTS
NORTH INTO CANADA...A TRAILING COLD FRONT IS THEN EXPECTED TO PUSH
THROUGH THE REGION TUESDAY. MODELS SOUNDINGS SHOW WEAK MID LEVEL LAPS
RATES...AND ELEVATED WARM LAYER. IN ADDITION...WINDS BEHIND FRONT
NEVER REALLY GAIN ANY NORTHERLY COMPONENT...AND WITH RIDGE AXIS
SOUTH OF THE AREA STILL STRETCHING AS FAR WEST AS TEXAS...DONT SEE
MUCH IN TERMS OF MOISTURE AVAILABILITY. ALL THINGS
CONSIDERED...SYSTEM DOES NOT LOOK TERRIBLY IMPRESSIVE SO ONLY
CALLING FOR SLIGHT CHANCE PRECIPITATION ALONG THE FRONT. AMPLIFIED
UPPER RIDGE THEN BUILDS OVERHEAD FOR THE MIDDLE OF NEXT WEEK WITH
THE NEXT SIGNIFICANT SYSTEM EXPECTED FRIDAY.

BMD

&&

.FIRE WEATHER...
330 AM CDT

ON MONDAY...SOUTH WINDS ARE EXPECTED TO INCREASE INTO THE 15 TO 25
MPH RANGE WITH SOME GUSTS TO 30 MPH OR SLIGHTLY HIGHER. THERE IS A
POSSIBILITY THAT SOME DRIER LOW LEVEL AIR MAY MIX DOWN TO THE
SURFACE WHICH WOULD RESULT IN MINIMUM AFTERNOON RELATIVE
HUMIDITIES AROUND OR LESS THAN 30 PERCENT. CONFIDENCE IN MEETING
RED FLAG CONDITIONS IS LOW AT THIS POINT GIVEN UNCERTAINTY AS TO
HOW MUCH OF THIS LOW LEVEL DRY AIR WILL MIX TO THE SURFACE...AND
ALSO 10 HR FUEL MOISTURES ARE STILL RUNNING ON THE HIGH SIDE
ACROSS THE AREA.

MARSILI

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 21Z...

GUSTY W/NW WINDS TO 25KTS THRU 02Z. WINDS BECOMING SOUTH AFT 15Z
SUN.

BEACHLER

//DISCUSSION...UPDATED 18Z...

THE WIND GUSTS WILL DECREASE SLIGHTLY AT SUNSET...AND WINDS
OVERNIGHT WILL BE BETWEEN 10-15 KNOTS. SKIES THIS AFTERNOON ARE
PARTLY CLOUDY WITH CUMULUS WHICH ARE LIKELY TO DIMINISH AFTER
SUNSET. THE WIND WILL BECOME MORE SOUTHERLY AT 5 TO 10 KNOTS
SUNDAY MORNING. THE WIND WILL BE SOUTH 5 TO 10 KNOTS THROUGH
SUNDAY AFTERNOON.

//ORD AND MDW CONFIDENCE...UPDATED 21Z...

HIGH CONFIDENCE IN WIND/SKY FORECAST.

BEACHLER

//OUTLOOK FOR ORD/MDW FOR 06Z MONDAY-12Z FRIDAY...UPDATED 18Z...

SUNDAY NIGHT...VFR. CHANCE OF RW.

MONDAY...VFR. SLIGHT CHANCE OF TSRA MONDAY NIGHT.

TUESDAY...VFR. CHANCE OF RW. SOME MVFR CEILINGS IN RW.

WEDNESDAY...VFR.

THURSDAY...VFR. SLIGHT CHANCE OF TSRA THURSDAY NIGHT.

FRIDAY...VFR. SLIGHT CHANCE OF TSRA.

&&

.MARINE...
151 PM CDT

THE LOW IN NORTHWEST QUEBEC WILL REMAIN IN NORTHWEST QUEBEC
THROUGH SUNDAY MORNING. THEN THE LOW MAY MOVE TO JUST WEST OF
JAMES BAY AFTER MIDNIGHT SUNDAY NIGHT. THE WIND WILL BE NORTHWEST
UNTIL VERY EARLY SUNDAY MORNING. A STRONG LOW WILL DEVELOP IN
WESTERN NEBRASKA SUNDAY AFTERNOON. THIS LOW WILL CAUSE THE WIND TO
BECOME SOUTH OVER LAKE MICHIGAN SUNDAY. THE SOUTHERN HALF OF THE
LAKE WILL HAVE A SOUTH WIND BY SUNDAY AFTERNOON AND THE NORTHERN
HALF WILL HAVE A SOUTH WIND BY SUNDAY EVENING. THE WIND SPEED WILL
BE 10 TO 15 KNOTS. THE WAVES WILL NOT BE AS LARGE AS THEY WERE
THIS SATURDAY MORNING.

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY...INDIANA NEARSHORE WATERS UNTIL 4 AM SUNDAY.

     SMALL CRAFT ADVISORY...ILLINOIS NEARSHORE WATERS UNTIL 10 PM SATURDAY.

&&

$$

000
FXUS63 KILX 042000
AFDILX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LINCOLN IL
300 PM CDT SAT SEP 4 2010

.DISCUSSION...
ISSUED 300 PM CDT SAT SEP 4 2010

SHORT TERM...TONIGHT THROUGH TUESDAY...
SURFACE HIGH PRESSURE FROM N TX INTO IA WILL MOVE EWD ACROSS THE
AREA TONIGHT. LIGHT WLY WINDS WILL BECOME SLY ON SUN AND BEGIN A
WARMING TREND THAT WILL CONTINUE INTO TUE. MODELS ARE PRODUCING SOME
MID LEVEL CLOUDS LATE TONIGHT ON THE LEADING EDGE OF THE MID/UPPER
LEVEL RIDGE THAT IS NOW COMING EWD INTO THE PLAINS. THESE SHOULD
MOVE N OF THE AREA DURING THE AFTERNOON...AND IT APPEARS THAT THE
BETTER CHANCES FOR SHOWERS WILL BE TO THE N OF CENTRAL IL SUN
AFTN/EVE WHERE WIND FIELDS WILL BE A BIT STRONGER AND TEMPERATURES
ALOFT COOLER. WARMER 850 MB TEMPERATURES ON SUN WILL MIX DOWN AND
RESULT IN MAXES A COUPLE OF CATEGORIES WARMER THAN TODAY...WITH MOST
AREAS SEEING HIGHS 75-80.

NEXT POTENTIAL WEATHER MAKER WILL BE A STRONG UPPER LOW THAT IS NOW
MOVING SEWD TOWARD THE PACIFIC NORTHWEST. BY LATE MON...THIS FEATURE
WILL BE COMING INTO THE PLAINS AND BY DAWN TUE MORN...THE ASSOCIATED
SURFACE LOW WILL BE NEAR THE WRN GREAT LAKES WITH A COLD FRONT
EXTENDING SWD INTO NWRN IL. MOISTURE RETURN AHEAD OF THE FRONT WILL
BE RATHER MEAGER INITIALLY...BUT MAY BE SUFFICIENT FOR SOME SHOWERS
ALONG AND IMMEDIATELY BEHIND THE FRONT. WILL KEEP SLIGHT CHANCE POPS
GOING FOR THE NW AFTER MIDNIGHT MON NIGHT...WITH A LITTLE HIGHER
POPS ON TUESDAY WITH FRONTAL PASSAGE. ANY PRECIPITATION THAT DOES
OCCUR SHOULD BE FAIRLY LIGHT GIVEN THE LIMITED AVAILABLE MOISTURE.
AHEAD OF THE FRONT...TEMPERATURES WILL CONTINUE THEIR WARMING TREND
WITH HIGHS ON TUE FROM THE MID 80S TO LOWER 90S IN THE CENTRAL AND
SE.

LONG TERM...WEDNESDAY THROUGH SUNDAY...
HIGH PRESSURE AND DRIER AIR BEHIND THE FRONT SHOULD KEEP WED MAINLY
DRY AND A BIT COOLER. THE MODELS HAVE BEEN DIFFERING ON HOW STRONGLY
THE SURFACE RIDGE WILL BUILD SWD INTO THE MIDWEST AND WHETHER THERE
WILL BE ANY LEFT-OVER SHOWERS IN SRN IL. BOTH THE GFS AND ECMWF
MODELS ARE PRETTY CLOSE IN SLOWING THE COLD FRONT IN SRN IL BUT THE
ECMWF PLACES POST-FRONTAL QPF FURTHER N INTO IL THAN THE GFS. THIS
IS ABOUT THE OPPOSITE OF WHAT EACH MODEL WAS INDICATING 12 HOURS
AGO...WHICH ADDS TO THE UNCERTAINTY. FOR NOW WILL KEEP SLIGHT CHANCE
POPS IN THE SE FOR WED.

THE STRENGTH/DEPTH OF THE WED SURFACE HIGH WILL ALSO HAVE AN IMPACT
ON WHEN THE NEXT CHANCE OF RAIN WILL BE. WITH THE UPPER PATTERN
BEING FAIRLY AMPLIFIED AS DEEP TROUGHS SET UP OVER BOTH COASTS...IT
SEEMS MORE PROBABLE THAT THE GFS MAY BE MORE REALISTIC IN PUSHING
THE HIGH PRESSURE FURTHER SOUTH THAN THE ECMWF. THUS WILL KEEP POPS
OUT OF WED NIGHT/THU. AFTER THAT...THE UPPER FLOW BECOMES SWLY AS
THE WRN UPPER TROUGH SWINGS NEWD INTO CANADA. THE STALLED FRONT TO
THE SOUTH WILL BE PULLED NORTHWARD AND POSSIBLY PRODUCE SOME
CONVECTION LATE THU NIGHT AND INTO FRI...FOLLOWED BY THE COLD FRONT
ON SUN. SINCE THE EXTENDED RANGE MODEL ENSEMBLES ARE SHOWING QUITE A
BIT OF SPREAD REGARDING THIS AS WELL AS THE PRECEDING MID-WEEK
SYSTEM...WILL KEEP POPS BELOW MENTIONABLE LEVELS FOR NOW.

04
&&

.AVIATION...
ISSUED 1233 PM CDT SAT SEP 4 2010

NORTHWESTERLY WINDS OF 10 TO 15KT WITH AN OCCASIONAL GUST TO 20KT
WILL CONTINUE THROUGH MID-AFTERNOON...BEFORE BEGINNING TO SUBSIDE
LATER TODAY. AS HIGH PRESSURE BUILDS EASTWARD ACROSS THE AREA THIS
EVENING...WINDS WILL GO LIGHT/VARIABLE FOR A TIME BEFORE A LIGHT
RETURN FLOW FROM THE S/SE DEVELOPS ACROSS THE WESTERN TERMINALS
OVERNIGHT. 12Z MODELS ARE SUGGESTING INCREASING MID-LEVEL MOISTURE
AS WARM AIR SURGES NORTHWARD ON THE BACK SIDE OF THE HIGH. WILL
INTRODUCE A BKN CLOUD DECK AT AROUND 12000FT AFTER 10Z AT KPIA AND
FURTHER EAST AT KBMI BY 15Z. FURTHER SOUTH AND EAST...WILL ONLY
CARRY SCT MID CLOUDS LATE TONIGHT INTO SUNDAY MORNING. WINDS ON
SUNDAY WILL SWITCH AROUND TO THE SOUTH AND WILL GUST UP TO 15KT
ACROSS MUCH OF THE AREA BY 18Z.

BARNES
&&

.ILX WATCHES/WARNINGS/ADVISORIES...
NONE.
&&

$$

000
FXUS63 KLOT 041947
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
247 PM CDT SAT SEP 4 2010

.DISCUSSION...
244 PM CDT

UNSEASONABLY COOL TEMPERATURES AND BREEZY CONDITIONS OCCURRED TODAY
AS A LOW PRESSURE SYSTEM DRIFTED SLOWLY EAST OVER WESTERN QUEBEC BUT
DO EXPECT WARMER WEATHER CONDITIONS TO FINISH OUT THIS HOLIDAY
WEEKEND. A TIGHT PRESSURE GRADIENT WILL CONTINUE TO RELAX OVER THE
NEXT 24 HOURS AS A RIDGE OF HIGH PRESSURE BEGINS TO MOVE INTO THE
UPPER MIDWEST. THIS WILL CAUSE WINDS TO WEAKEN AND EVENTUALLY SHIFT
TO MORE SOUTHERLY ON SUNDAY AS THE RIDGE AXIS SHIFTS TO THE EAST OF
THE FORECAST AREA. THIS WILL ALLOW WARMER AIR TO ENTER THE
REGION...THUS CONTINUE TO CALL FOR AN 8-10F WARMING TREND EACH DAY
FOR THE NEXT COUPLE DAYS. H85 TEMPS IN THE LOW SINGLE DIGITS TODAY
WILL GRADUALLY WARM TO NEAR 20C BY MONDAY AFTERNOON AS A LOW
PRESSURE SYSTEM DEVELOPS OVER THE NORTHERN PLAINS AND SOUTHWESTERLY
FLOW INCREASES.

A WEAK WARM FRONT PASSES THROUGH SUNDAY NIGHT INTO MONDAY
MORNING...HOWEVER DUE TO THE ALIGNMENT OF THE RIDGE AXIS WHICH
EXTENDS SOUTHWEST INTO LOUISIANA...MOISTURE AVAILABILITY WILL BE A
LIMITING FACTOR FOR ANY WIDESPREAD PRECIPITATION. MODELS INDICATE A
DRY FRONTAL PASSAGE AND PRECIP IS EXPECTED TO OCCUR FURTHER NORTH
WHERE MORE FAVORABLE ISENTROPIC LIFT IS OCCURRING. AS THE LOW LIFTS
NORTH INTO CANADA...A TRAILING COLD FRONT IS THEN EXPECTED TO PUSH
THROUGH THE REGION TUESDAY. MODELS SOUNDINGS SHOW WEAK MID LEVEL LAPS
RATES...AND ELEVATED WARM LAYER. IN ADDITION...WINDS BEHIND FRONT
NEVER REALLY GAIN ANY NORTHERLY COMPONENT...AND WITH RIDGE AXIS
SOUTH OF THE AREA STILL STRETCHING AS FAR WEST AS TEXAS...DONT SEE
MUCH IN TERMS OF MOISTURE AVAILABILITY. ALL THINGS
CONSIDERED...SYSTEM DOES NOT LOOK TERRIBLY IMPRESSIVE SO ONLY
CALLING FOR SLIGHT CHANCE PRECIPITATION ALONG THE FRONT. AMPLIFIED
UPPER RIDGE THEN BUILDS OVERHEAD FOR THE MIDDLE OF NEXT WEEK WITH
THE NEXT SIGNIFICANT SYSTEM EXPECTED FRIDAY.

BMD

&&

.FIRE WEATHER...
330 AM CDT

ON MONDAY...SOUTH WINDS ARE EXPECTED TO INCREASE INTO THE 15 TO 25
MPH RANGE WITH SOME GUSTS TO 30 MPH OR SLIGHTLY HIGHER. THERE IS A
POSSIBILITY THAT SOME DRIER LOW LEVEL AIR MAY MIX DOWN TO THE
SURFACE WHICH WOULD RESULT IN MINIMUM AFTERNOON RELATIVE
HUMIDITIES AROUND OR LESS THAN 30 PERCENT. CONFIDENCE IN MEETING
RED FLAG CONDITIONS IS LOW AT THIS POINT GIVEN UNCERTAINTY AS TO
HOW MUCH OF THIS LOW LEVEL DRY AIR WILL MIX TO THE SURFACE...AND
ALSO 10 HR FUEL MOISTURES ARE STILL RUNNING ON THE HIGH SIDE
ACROSS THE AREA.

MARSILI

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 18Z...

THIS AFTERNOON THERE WILL BE WEST TO NORTHWEST WIND GUSTS WHICH
WILL GUST UP TO 25 KNOTS. VFR CONDITIONS WILL PREVAIL WITH SCATTERED
CLOUDS 2500 TO 4000 FEET.

//DISCUSSION...UPDATED 18Z...

THE WIND GUSTS WILL DECREASE SLIGHTLY AT SUNSET...AND WINDS
OVERNIGHT WILL BE BETWEEN 10-15 KNOTS. SKIES THIS AFTERNOON ARE
PARTLY CLOUDY WITH CUMULUS WHICH ARE LIKELY TO DIMINISH AFTER
SUNSET. THE WIND WILL BECOME MORE SOUTHERLY AT 5 TO 10 KNOTS
SUNDAY MORNING. THE WIND WILL BE SOUTH 5 TO 10 KNOTS THROUGH
SUNDAY AFTERNOON.

//ORD AND MDW CONFIDENCE...UPDATED 18Z...

HIGH CONFIDENCE IN THE WIND AND SKY FORECASTS.

//OUTLOOK FOR ORD/MDW FOR 06Z MONDAY-12Z SATURDAY...UPDATED 18Z...

SUNDAY NIGHT...VFR. CHANCE OF RW.

MONDAY...VFR. SLIGHT CHANCE OF TSRA MONDAY NIGHT.

TUESDAY...VFR. CHANCE OF RW. SOME MVFR CEILINGS IN RW.

WEDNESDAY...VFR.

THURSDAY...VFR. SLIGHT CHANCE OF TSRA THURSDAY NIGHT.

FRIDAY...VFR. SLIGHT CHANCE OF TSRA.

&&

.MARINE...
151 PM CDT

THE LOW IN NORTHWEST QUEBEC WILL REMAIN IN NORTHWEST QUEBEC
THROUGH SUNDAY MORNING. THEN THE LOW MAY MOVE TO JUST WEST OF
JAMES BAY AFTER MIDNIGHT SUNDAY NIGHT. THE WIND WILL BE NORTHWEST
UNTIL VERY EARLY SUNDAY MORNING. A STRONG LOW WILL DEVELOP IN
WESTERN NEBRASKA SUNDAY AFTERNOON. THIS LOW WILL CAUSE THE WIND TO
BECOME SOUTH OVER LAKE MICHIGAN SUNDAY. THE SOUTHERN HALF OF THE
LAKE WILL HAVE A SOUTH WIND BY SUNDAY AFTERNOON AND THE NORTHERN
HALF WILL HAVE A SOUTH WIND BY SUNDAY EVENING. THE WIND SPEED WILL
BE 10 TO 15 KNOTS. THE WAVES WILL NOT BE AS LARGE AS THEY WERE
THIS SATURDAY MORNING.

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...GALE WARNING...LMZ261-LMZ362-LMZ364-LMZ563 UNTIL 3 PM SATURDAY.

     SMALL CRAFT ADVISORY...INDIANA NEARSHORE WATERS UNTIL 4 AM SUNDAY.

     SMALL CRAFT ADVISORY...ILLINOIS NEARSHORE WATERS UNTIL 4 PM SATURDAY.

&&

$$

000
FXUS63 KLOT 041915
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
215 PM CDT SAT SEP 4 2010

.DISCUSSION...
330 AM CDT

FORECAST FOCUS CONTINUES TO CENTER ON A FAIRLY ACTIVE PATTERN IN
TERMS OF FRONTAL PROGRESSIONS ANTICIPATED FOR THE UPCOMING
WEEK...ALTHOUGH PRECIPITATION CHANCES WILL BE SOMEWHAT LIMITED WITH
MOISTURE AVAILABILITY QUESTIONS.

WATER VAPOR IMAGERY EARLY THIS MORNING INDICATING UPPER LOW SPINNING
ACROSS FAR SOUTHERN ONTARIO WITH CHANNELED UPPER LEVEL VORT DIGGING
THROUGH BASE OF THIS TROUGH ACROSS THE MID/UPPER MS RIVER VALLEY IN
ASSOCIATION WITH THE UPPER LEVEL JET. SURFACE OBS AND RADAR
IMAGERY HAVE INDICATED BRIEF PERIODS OF SPRINKLES OVER PAST FEW
HOURS LIKELY IN ASSOCIATION WITH WEAK DPVA AND WEAK LOW LEVEL
FRONTOGENESIS. LOW LEVEL COLD ADVECTION ASSOCIATED WITH THIS
BAROCLINIC ZONE WILL USHER IN EVEN COOLER TEMPS THAN
YESTERDAY...ALTHOUGH PLENTY OF INSOLATION AND DEEPER MIXING MAY
PARTIALLY OFFSET THE COOLER LOW LEVEL TEMPERATURES TODAY. TAKING
THE ABOVE INTO CONSIDERATION...HAVE GENERALLY MAINTAINED IDEA OF
TEMPERATURES A FEW DEGREES COOLER TODAY THAN YESTERDAY...IN THE
MID TO UPPER 60S. IN TERMS OF SKY COVER...THE PATCHY STRATOCU
EXTENDING FROM NORTH CENTRAL ILLINOIS INTO THE CHICAGO METRO AREA
SHOULD CONTINUE TO SHIFT EAST/SOUTHEAST THIS MORNING...AND WILL
BE REPLACED BY SOME DIURNAL FLAT CU DEVELOPMENT. SOME LIGHT LAKE
EFFECT RAIN SHOWERS WILL LIKELY REMAIN JUST TO THE EAST/NORTHEAST
OF PORTER COUNTY INDIANA...ESPECIALLY CONSIDERING LOW LEVEL WINDS
SHOULD BEGIN TO BACK THIS MORNING AS A LOW LEVEL RIDGE SINKS
SOUTHEASTWARD INTO THE MID MS RIVER VALLEY.

TEMPERATURE ADVECTION TO BECOME MORE NEUTRAL TONIGHT...ALTHOUGH A
BETTER CHANCE FOR COOLISH LOWS IN THE MID 40S IN STORE FOR TONIGHT
GIVEN GREATER DECOUPLING POTENTIAL GIVEN PROXIMITY OF SFC RIDGE
AXIS. WOULD SUSPECT THAT SOME OF THE FAVORED LOW LYING COOL SPOTS
MAY EVEN FLIRT WITH 40 DEGREES FOR MINS TONIGHT.

ON SUNDAY...SFC LOW IS EXPECTED TO DEEPEN ACROSS THE CENTRAL HIGH
PLAINS AS NEXT SIGNIFICANT UPPER LEVEL TROUGH MOVES ACROSS NWRN
CONUS. THE LOW LEVEL RIDGE SETTLING INTO LOWER/MID MS RIVER VALLEY
OVER NEXT 24 HOURS WILL LIMIT MOISTURE RETURN INITIALLY IN ADVANCE
OF THIS TROUGH. GIVEN INCREASING UNCERTAINTY OF LOW LEVEL
MOISTURE AVAILABILITY...DID GO AHEAD AND PULL THE SLIGHT CHANCE
POPS FOR RAIN SHOWERS SUNDAY AFTERNOON. BY SUNDAY
EVENING...ISENTROPIC LIFT SHOULD BEGIN TO STRENGTHEN MORE
SUBSTANTIALLY WITH SOME BETTER MID LEVEL LAPSE RATES DEVELOPING.
AT THIS POINT...WOULD SUSPECT THAT THE BEST CHANCE OF ELEVATED
SHOWERS/STORMS WOULD BE JUST NORTH OF FORECAST AREA ACROSS WI AND
INTO THE UPPER GREAT LAKES AS ZONE OF STRONGER ISENTROPIC ASCENT
LIFTS NORTHWARD WITH THE WARM FRONTAL-LIKE FEATURE. THIS ALSO
APPEARS TO BE A MORE SYNOPTICALLY FAVORED REGION FOR LARGE SCALE
ASCENT WITH WEAK UPPER JET STREAK COUPLING NOTED IN NAM/GFS SOLUTIONS.

LOW/MID LEVELS SHOULD DRY OUT BY EARLY MONDAY AS LOW LEVEL WARM
FRONTS LIFTS THROUGH NORTHERN GREAT LAKES AND THUS DRY CONDITIONS
EXPECTED TO CONTINUE THROUGH THE DAY MONDAY. UPPER DYNAMICS
ASSOCIATED WITH THE AFOREMENTIONED UPPER TROUGH WILL BEGIN TO
INCREASE BY MONDAY NIGHT...BUT ESPECIALLY AGAIN TO THE NORTH OF
THE AREA. THUS...WILL HANDLE MONDAY NIGHT PERIOD WITH JUST SLIGHT
CHANCE POPS FOR TSRA. TEMPERATURES ON MONDAY IN THE WARM SECTOR
SHOULD SHOOT BACK UP INTO THE LOWER TO MID 80S ACROSS MUCH OF THE
AREA...AND WITH THIS WARMING AND INITIALLY DRY LOW LEVELS COMES
SOME CONCERN FOR FIRE WEATHER...WHICH IS HIGHLIGHTED BELOW.

SYSTEM WILL OCCLUDE ACROSS UPPER MIDWEST TUESDAY WITH COLD FRONT
EXPECTED TO STALL OUT ACROSS OR JUST THE SOUTH OF THE AREA...AND
THEN BEGIN TO RETURN NORTHWARD AS A WARM FRONT AGAIN TOWARD THE END
OF THE WEEK. THIS RETURN WARM/MOIST ADVECTION COULD BE CONDUCIVE FOR
SOME SCT SHOWERS/STORMS BY THURS. HOWEVER...MEDIUM RANGE MODELS
DIVERGE TO A LARGER DEGREE WITH NEXT SHORT WAVE TROUGH FOR
THURS/FRI WITH ECMWF A SIGNIFICANTLY SLOWER SOLUTION COMPARED TO
GFS/NCEP ENSEMBLES. CONFIDENCE IN TIMING PRECIP CHANCES IS LOW AT
THIS TIME...SO DID NOT CHANGE LOW CHANCE POPS THURS/FRI...WITH SOME
HIGHER CONFIDENCE IN AT LEAST A SHIFT BACK TO WARMER TEMPS AGAIN
TOWARD THE END OF THE PERIOD.

MARSILI

&&

.FIRE WEATHER...
330 AM CDT

ON MONDAY...SOUTH WINDS ARE EXPECTED TO INCREASE INTO THE 15 TO 25
MPH RANGE WITH SOME GUSTS TO 30 MPH OR SLIGHTLY HIGHER. THERE IS A
POSSIBILITY THAT SOME DRIER LOW LEVEL AIR MAY MIX DOWN TO THE
SURFACE WHICH WOULD RESULT IN MINIMUM AFTERNOON RELATIVE
HUMIDITIES AROUND OR LESS THAN 30 PERCENT. CONFIDENCE IN MEETING
RED FLAG CONDITIONS IS LOW AT THIS POINT GIVEN UNCERTAINTY AS TO
HOW MUCH OF THIS LOW LEVEL DRY AIR WILL MIX TO THE SURFACE...AND
ALSO 10 HR FUEL MOISTURES ARE STILL RUNNING ON THE HIGH SIDE
ACROSS THE AREA.

MARSILI

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 18Z...

THIS AFTERNOON THERE WILL BE WEST TO NORTHWEST WIND GUSTS WHICH
WILL GUST UP TO 25 KNOTS. VFR CONDITIONS WILL PREVAIL WITH SCATTERED
CLOUDS 2500 TO 4000 FEET.

//DISCUSSION...UPDATED 18Z...

THE WIND GUSTS WILL DECREASE SLIGHTLY AT SUNSET...AND WINDS
OVERNIGHT WILL BE BETWEEN 10-15 KNOTS. SKIES THIS AFTERNOON ARE
PARTLY CLOUDY WITH CUMULUS WHICH ARE LIKELY TO DIMINISH AFTER
SUNSET. THE WIND WILL BECOME MORE SOUTHERLY AT 5 TO 10 KNOTS
SUNDAY MORNING. THE WIND WILL BE SOUTH 5 TO 10 KNOTS THROUGH
SUNDAY AFTERNOON.

//ORD AND MDW CONFIDENCE...UPDATED 18Z...

HIGH CONFIDENCE IN THE WIND AND SKY FORECASTS.

//OUTLOOK FOR ORD/MDW FOR 06Z MONDAY-12Z SATURDAY...UPDATED 18Z...

SUNDAY NIGHT...VFR. CHANCE OF RW.

MONDAY...VFR. SLIGHT CHANCE OF TSRA MONDAY NIGHT.

TUESDAY...VFR. CHANCE OF RW. SOME MVFR CEILINGS IN RW.

WEDNESDAY...VFR.

THURSDAY...VFR. SLIGHT CHANCE OF TSRA THURSDAY NIGHT.

FRIDAY...VFR. SLIGHT CHANCE OF TSRA.

&&

.MARINE...
151 PM CDT

THE LOW IN NORTHWEST QUEBEC WILL REMAIN IN NORTHWEST QUEBEC
THROUGH SUNDAY MORNING. THEN THE LOW MAY MOVE TO JUST WEST OF
JAMES BAY AFTER MIDNIGHT SUNDAY NIGHT. THE WIND WILL BE NORTHWEST
UNTIL VERY EARLY SUNDAY MORNING. A STRONG LOW WILL DEVELOP IN
WESTERN NEBRASKA SUNDAY AFTERNOON. THIS LOW WILL CAUSE THE WIND TO
BECOME SOUTH OVER LAKE MICHIGAN SUNDAY. THE SOUTHERN HALF OF THE
LAKE WILL HAVE A SOUTH WIND BY SUNDAY AFTERNOON AND THE NORTHERN
HALF WILL HAVE A SOUTH WIND BY SUNDAY EVENING. THE WIND SPEED WILL
BE 10 TO 15 KNOTS. THE WAVES WILL NOT BE AS LARGE AS THEY WERE
THIS SATURDAY MORNING.

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...GALE WARNING...LMZ261-LMZ362-LMZ364-LMZ563 UNTIL 3 PM SATURDAY.

     SMALL CRAFT ADVISORY...INDIANA NEARSHORE WATERS UNTIL 4 AM SUNDAY.

     SMALL CRAFT ADVISORY...ILLINOIS NEARSHORE WATERS UNTIL 4 PM SATURDAY.

&&

$$

000
FXUS63 KLOT 041849
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
149 PM CDT SAT SEP 4 2010

.DISCUSSION...
330 AM CDT

FORECAST FOCUS CONTINUES TO CENTER ON A FAIRLY ACTIVE PATTERN IN
TERMS OF FRONTAL PROGRESSIONS ANTICIPATED FOR THE UPCOMING
WEEK...ALTHOUGH PRECIPITATION CHANCES WILL BE SOMEWHAT LIMITED WITH
MOISTURE AVAILABILITY QUESTIONS.

WATER VAPOR IMAGERY EARLY THIS MORNING INDICATING UPPER LOW SPINNING
ACROSS FAR SOUTHERN ONTARIO WITH CHANNELED UPPER LEVEL VORT DIGGING
THROUGH BASE OF THIS TROUGH ACROSS THE MID/UPPER MS RIVER VALLEY IN
ASSOCIATION WITH THE UPPER LEVEL JET. SURFACE OBS AND RADAR
IMAGERY HAVE INDICATED BRIEF PERIODS OF SPRINKLES OVER PAST FEW
HOURS LIKELY IN ASSOCIATION WITH WEAK DPVA AND WEAK LOW LEVEL
FRONTOGENESIS. LOW LEVEL COLD ADVECTION ASSOCIATED WITH THIS
BAROCLINIC ZONE WILL USHER IN EVEN COOLER TEMPS THAN
YESTERDAY...ALTHOUGH PLENTY OF INSOLATION AND DEEPER MIXING MAY
PARTIALLY OFFSET THE COOLER LOW LEVEL TEMPERATURES TODAY. TAKING
THE ABOVE INTO CONSIDERATION...HAVE GENERALLY MAINTAINED IDEA OF
TEMPERATURES A FEW DEGREES COOLER TODAY THAN YESTERDAY...IN THE
MID TO UPPER 60S. IN TERMS OF SKY COVER...THE PATCHY STRATOCU
EXTENDING FROM NORTH CENTRAL ILLINOIS INTO THE CHICAGO METRO AREA
SHOULD CONTINUE TO SHIFT EAST/SOUTHEAST THIS MORNING...AND WILL
BE REPLACED BY SOME DIURNAL FLAT CU DEVELOPMENT. SOME LIGHT LAKE
EFFECT RAIN SHOWERS WILL LIKELY REMAIN JUST TO THE EAST/NORTHEAST
OF PORTER COUNTY INDIANA...ESPECIALLY CONSIDERING LOW LEVEL WINDS
SHOULD BEGIN TO BACK THIS MORNING AS A LOW LEVEL RIDGE SINKS
SOUTHEASTWARD INTO THE MID MS RIVER VALLEY.

TEMPERATURE ADVECTION TO BECOME MORE NEUTRAL TONIGHT...ALTHOUGH A
BETTER CHANCE FOR COOLISH LOWS IN THE MID 40S IN STORE FOR TONIGHT
GIVEN GREATER DECOUPLING POTENTIAL GIVEN PROXIMITY OF SFC RIDGE
AXIS. WOULD SUSPECT THAT SOME OF THE FAVORED LOW LYING COOL SPOTS
MAY EVEN FLIRT WITH 40 DEGREES FOR MINS TONIGHT.

ON SUNDAY...SFC LOW IS EXPECTED TO DEEPEN ACROSS THE CENTRAL HIGH
PLAINS AS NEXT SIGNIFICANT UPPER LEVEL TROUGH MOVES ACROSS NWRN
CONUS. THE LOW LEVEL RIDGE SETTLING INTO LOWER/MID MS RIVER VALLEY
OVER NEXT 24 HOURS WILL LIMIT MOISTURE RETURN INITIALLY IN ADVANCE
OF THIS TROUGH. GIVEN INCREASING UNCERTAINTY OF LOW LEVEL
MOISTURE AVAILABILITY...DID GO AHEAD AND PULL THE SLIGHT CHANCE
POPS FOR RAIN SHOWERS SUNDAY AFTERNOON. BY SUNDAY
EVENING...ISENTROPIC LIFT SHOULD BEGIN TO STRENGTHEN MORE
SUBSTANTIALLY WITH SOME BETTER MID LEVEL LAPSE RATES DEVELOPING.
AT THIS POINT...WOULD SUSPECT THAT THE BEST CHANCE OF ELEVATED
SHOWERS/STORMS WOULD BE JUST NORTH OF FORECAST AREA ACROSS WI AND
INTO THE UPPER GREAT LAKES AS ZONE OF STRONGER ISENTROPIC ASCENT
LIFTS NORTHWARD WITH THE WARM FRONTAL-LIKE FEATURE. THIS ALSO
APPEARS TO BE A MORE SYNOPTICALLY FAVORED REGION FOR LARGE SCALE
ASCENT WITH WEAK UPPER JET STREAK COUPLING NOTED IN NAM/GFS SOLUTIONS.

LOW/MID LEVELS SHOULD DRY OUT BY EARLY MONDAY AS LOW LEVEL WARM
FRONTS LIFTS THROUGH NORTHERN GREAT LAKES AND THUS DRY CONDITIONS
EXPECTED TO CONTINUE THROUGH THE DAY MONDAY. UPPER DYNAMICS
ASSOCIATED WITH THE AFOREMENTIONED UPPER TROUGH WILL BEGIN TO
INCREASE BY MONDAY NIGHT...BUT ESPECIALLY AGAIN TO THE NORTH OF
THE AREA. THUS...WILL HANDLE MONDAY NIGHT PERIOD WITH JUST SLIGHT
CHANCE POPS FOR TSRA. TEMPERATURES ON MONDAY IN THE WARM SECTOR
SHOULD SHOOT BACK UP INTO THE LOWER TO MID 80S ACROSS MUCH OF THE
AREA...AND WITH THIS WARMING AND INITIALLY DRY LOW LEVELS COMES
SOME CONCERN FOR FIRE WEATHER...WHICH IS HIGHLIGHTED BELOW.

SYSTEM WILL OCCLUDE ACROSS UPPER MIDWEST TUESDAY WITH COLD FRONT
EXPECTED TO STALL OUT ACROSS OR JUST THE SOUTH OF THE AREA...AND
THEN BEGIN TO RETURN NORTHWARD AS A WARM FRONT AGAIN TOWARD THE END
OF THE WEEK. THIS RETURN WARM/MOIST ADVECTION COULD BE CONDUCIVE FOR
SOME SCT SHOWERS/STORMS BY THURS. HOWEVER...MEDIUM RANGE MODELS
DIVERGE TO A LARGER DEGREE WITH NEXT SHORT WAVE TROUGH FOR
THURS/FRI WITH ECMWF A SIGNIFICANTLY SLOWER SOLUTION COMPARED TO
GFS/NCEP ENSEMBLES. CONFIDENCE IN TIMING PRECIP CHANCES IS LOW AT
THIS TIME...SO DID NOT CHANGE LOW CHANCE POPS THURS/FRI...WITH SOME
HIGHER CONFIDENCE IN AT LEAST A SHIFT BACK TO WARMER TEMPS AGAIN
TOWARD THE END OF THE PERIOD.

MARSILI

&&

.FIRE WEATHER...
330 AM CDT

ON MONDAY...SOUTH WINDS ARE EXPECTED TO INCREASE INTO THE 15 TO 25
MPH RANGE WITH SOME GUSTS TO 30 MPH OR SLIGHTLY HIGHER. THERE IS A
POSSIBILITY THAT SOME DRIER LOW LEVEL AIR MAY MIX DOWN TO THE
SURFACE WHICH WOULD RESULT IN MINIMUM AFTERNOON RELATIVE
HUMIDITIES AROUND OR LESS THAN 30 PERCENT. CONFIDENCE IN MEETING
RED FLAG CONDITIONS IS LOW AT THIS POINT GIVEN UNCERTAINTY AS TO
HOW MUCH OF THIS LOW LEVEL DRY AIR WILL MIX TO THE SURFACE...AND
ALSO 10 HR FUEL MOISTURES ARE STILL RUNNING ON THE HIGH SIDE
ACROSS THE AREA.

MARSILI

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 18Z...

THIS AFTERNOON THERE WILL BE WEST TO NORTHWEST WIND GUSTS WHICH
WILL GUST UP TO 25KT. VFR CONDITIONS WILL PREVAIL WITH SCATTERED
CLOUDS 2500 TO 4000 FEET.

//DISCUSSION...UPDATED 18Z...

THE WIND GUSTS WILL DECREASE SLIGHTLY AT SUNSET...AND WINDS
OVERNIGHT WILL BE BETWEEN 10-15 KNOTS. SKIES THIS AFTERNOON ARE
PARTLY CLOUDY WITH CUMULUS WHICH ARE LIKELY TO DIMINISH AFTER
SUNSET. THE WIND WILL BECOME MORE SOUTHERLY AT 5 TO 10 KNOTS
SUNDAY MORNING. THE WIND WILL BE SOUTH 5 TO 10 KNOTS THROUGH
SUNDAY AFTERNOON.

//ORD AND MDW CONFIDENCE...UPDATED 18Z...

HIGH CONFIDENCE IN THE WIND AND SKY FORECASTS.

//OUTLOOK FOR ORD/MDW FOR 06Z MONDAY-12Z SATURDAY...UPDATED 18Z...

SUNDAY NIGHT...VFR. CHANCE OF RW.

MONDAY...VFR. SLIGHT CHANCE OF TSRA MONDAY NIGHT.

TUESDAY...VFR. CHANCE OF RW. SOME MVFR CEILINGS IN RW.

WEDNESDAY...VFR.

THURSDAY...VFR. SLIGHT CHANCE OF TSRA THURSDAY NIGHT.

FRIDAY...VFR. SLIGHT CHANCE OF TSRA.

&&

.MARINE...
215 AM CDT

SEEING SIGNS OF THE PRESSURE GRADIENT AND WINDS STARTING TO SLOWLY
EASE OVER THE LAKE...WITH NO GALE FORCE GUSTS FOR THE PAST COUPLE
HOURS AT THE SOUTH BUOY AND WINDS DOWN A BIT NORTH BUOY. STILL
SEEING GUSTS TO AROUND GALE FORCE AT SOME OF THE COASTAL OB SITES
ALONG THE EASTERN SHORES...SO PLAN TO HANG ONTO THE GL.W UNTIL MID
MORNING SOUTH. FARTHER NORTH GRADIENT MAY BE A BIT SLOWER TO RELAX
AND WILL HANG ONTO GALES THERE INTO THE EARLY AFTERNOON. WINDS RELAX
FURTHER TONIGHT INTO SUNDAY AS THEY GRADUALLY BACK TO A MORE
SOUTHERLY DIRECTION AS HIGH MOVES EAST INTO THE OHIO VALLEY AND THE
NEXT LOW DEVELOPS OVER THE PLAINS.

SOUTHERLY GRADIENT WILL TIGHTEN UP CONSIDERABLY MONDAY INTO MONDAY
NIGHT AS LOW TRACKS FROM THE CENTRAL PLAINS INTO THE UPPER GREAT
LAKES. MODELS CONTINUE TO SUGGEST THAT WE COULD BE LOOKING AT
SOUTHERLY GALES DURING THIS TIME RANGE OVER SOUTHERN 1/2 TO 2/3 OF
THE LAKE...AND THEN SOUTHWEST GALES OVER NORTHERN LAKE MICHIGAN MON
NIGHT INTO TUES AS THE LOW PULLS OUT AND SLOWLY WEAKENS. BUT MODELS
ARE ALSO SHOWING THE BOUNDARY LAYER REMAINING WELL MIXED OVER THE
LAKE...WHICH MAY NOT BE THE CASE.  COLD AIR ADVECTION AND UPWELLING
FROM THE LARGE WAVES THIS WEEKEND MAY KNOCK DOWN WATER TEMPS LEADING
TO MORE STABLE CONDITIONS OVER THE LAKE THAN MODEL SOUNDINGS
SUGGEST...SO HAVE OPTED TO STICK WITH JUST 30KT WINDS FOR NOW AND
RE-ACCESS THINGS OVER THE WEEKEND BEFORE BUMPING UP WINDS TO GALES.

FOR THE NEARSHORE WILL BE KILLING THE GALE WARNING WITH THIS
MORNING`S ISSUANCE AND REPLACING WITH A SMALL CRAFT ADV THRU THE
AFTERNOON FOR THE ILLINOIS SHORE WHERE WAVES OUT TOWARD THE 5 MILE
OFF SHORE RANGE MAY STILL BE NEAR CRITERIA AND WHERE GUSTS COULD
GET UP TO AROUND CRITERIA AS WELL. FOR THE INDIANA SHORE WHERE THE
FETCH IS LONGER PLAN TO HANG ONTO THE ADV THRU TONIGHT TO GIVE THE
WAVES TIME TO FULLY SUBSIDE.

IZZI

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...GALE WARNING...LMZ261-LMZ362-LMZ364-LMZ563 UNTIL 3 PM SATURDAY.

     SMALL CRAFT ADVISORY...INDIANA NEARSHORE WATERS UNTIL 4 AM SUNDAY.

     SMALL CRAFT ADVISORY...ILLINOIS NEARSHORE WATERS UNTIL 4 PM SATURDAY.

&&

$$

000
FXUS63 KILX 041733
AFDILX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LINCOLN IL
1233 PM CDT SAT SEP 4 2010

.DISCUSSION...
ISSUED 1038 AM CDT SAT SEP 4 2010

SUNNY AND COOL CONDITIONS PREVAIL ACROSS CENTRAL ILLINOIS THIS
MORNING...WITH 15Z TEMPS RANGING FROM THE LOWER 60S NORTH TO
AROUND 70 DEGREES FAR SOUTHEAST. CU-RULE INDICATES FEW-SCT CU
DEVELOPING TODAY AND LATEST SATELLITE IMAGERY SUPPORTS THIS. HAVE
MADE SOME ADJUSTMENTS TO HOURLY TEMPS AND AFTERNOON HIGHS...MAINLY
TO INCREASE READINGS SOUTH OF I-70 BY A COUPLE OF DEGREES. CHANGES
ARE MINOR AND DO NOT REQUIRE A ZONE UPDATE AT THIS TIME.

&&

.AVIATION...
ISSUED 1233 PM CDT SAT SEP 4 2010

NORTHWESTERLY WINDS OF 10 TO 15KT WITH AN OCCASIONAL GUST TO 20KT
WILL CONTINUE THROUGH MID-AFTERNOON...BEFORE BEGINNING TO SUBSIDE
LATER TODAY. AS HIGH PRESSURE BUILDS EASTWARD ACROSS THE AREA THIS
EVENING...WINDS WILL GO LIGHT/VARIABLE FOR A TIME BEFORE A LIGHT
RETURN FLOW FROM THE S/SE DEVELOPS ACROSS THE WESTERN TERMINALS
OVERNIGHT. 12Z MODELS ARE SUGGESTING INCREASING MID-LEVEL MOISTURE
AS WARM AIR SURGES NORTHWARD ON THE BACK SIDE OF THE HIGH. WILL
INTRODUCE A BKN CLOUD DECK AT AROUND 12000FT AFTER 10Z AT KPIA AND
FURTHER EAST AT KBMI BY 15Z. FURTHER SOUTH AND EAST...WILL ONLY
CARRY SCT MID CLOUDS LATE TONIGHT INTO SUNDAY MORNING. WINDS ON
SUNDAY WILL SWITCH AROUND TO THE SOUTH AND WILL GUST UP TO 15KT
ACROSS MUCH OF THE AREA BY 18Z.

BARNES
&&

.PREV DISCUSSION...
ISSUED 330 AM CDT SAT SEP 4 2010

00Z MODELS ARE IN FAIR AGREEMENT THIS LABOR DAY WEEKEND ALONG
WITH MET AND MAV TEMPERATURE GUIDANCE. NOT TOO MANY CHANGES
PLANNED IN THIS FORECAST PACKAGE AS NICE WEATHER PREVAILS THROUGH
EARLY NEXT WEEK. BELOW NORMAL TEMPERATURES THIS WEEKEND GRADUALLY
MODIFY BACK ABOVE NORMAL MONDAY WITH BREEZY SSW FLOW AS HIGH
PRESSURE RIDGE DRIFTS EAST OF IL SUN/MON.

SHORT TERM...TODAY THROUGH MONDAY NIGHT.

STRONG LOW PRESSURE OF 992 MB OVER EASTERN ONTARIO ALONG WITH
STRONG 500 MB LOW OF 545 DM TO MOVE EAST WHILE 1022 MB HIGH
PRESSURE RIDGE OVER THE GREAT PLAINS DRIFTS EAST OVER IL TONIGHT.
HIGH PRESSURE THEN DRIFTS EAST OF IL SUNDAY AND INTO THE MID
ATLANTIC STATES SUNDAY NIGHT/MON. EXPECT MOSTLY SUNNY SKIES TODAY
WITH SCATTERED CUMULUS CLOUDS AND NW WINDS 10 TO 15 MPH AND GUSTS
UP TO 20-25 MPH THIS AFTERNOON ESPECIALLY FROM I-74 NE. HIGHS IN
THE LOWER 70S TODAY WITH AREAS FROM I-74 NE NEAR 70F. COOLEST DAY
IN CENTRAL IL SINCE MAY 21ST. TONIGHT WILL BE THE COOLEST NIGHT
WITH HIGH PRESSURE RIDGE NEARBY BRINGING CLEAR SKIES AND LIGHT
WINDS WITH LOWS IN THE MID TO UPPER 40S (COOLEST IN EAST CENTRAL IL).
MOSTLY SUNNY SKIES SUNDAY WITH MILDER HIGHS IN THE UPPER 70S TO
NEAR 80F SW AREAS.

MODELS BUILDING UPPER LEVEL RIDGE OVER THE OHIO VALLEY MONDAY
(LABOR DAY) WITH STRONG LOW PRESSURE 998 MB MOVING INTO THE UPPER
MS VALLEY. TIGHTENING PRESSURE GRADIENT OVER IL TO INCREASE SSW
WINDS ALONG WITH WARMER TEMPS IN THE MID 80S CENTRAL IL AND UPPER
80S SE IL. ADDED JUST A SLIGHT CHANCE OF A SHOWER OR THUNDERSTORM
LATER MONDAY NIGHT OVER THE IL RIVER VALLEY WITH A WEAKENING FRONTAL
BOUNDARY MOVING INTO NW IL AS STRONG LOW PRESSURE PASSES WELL
NORTH OF IL INTO NORTHERN WI.

LONG TERM...TUESDAY THROUGH FRIDAY.

WEAKENING FRONT MOVES SE THROUGH CENTRAL/SE IL TUE AND TOWARD THE
OHIO RIVER BY DAWN WED. BEST MOISTURE APPEARS SOUTH OF CENTRAL IL
WHILE BEST UPPER LEVEL DYNAMICS NORTH OVER THE GREAT LAKES. SO
JUST SLIGHT CHANCES OF SHOWERS AND THUNDERSTORMS AND BEST CHANCES
SOUTHERN AREAS. FRONT APPEARS TO MOVE BACK NORTH THU NIGHT AND FRI
AS UPPER LEVEL RIDGE BUILDS BACK INTO THE MS VALLEY RETURNING
WARMER WX.

HUETTL

&&

.ILX WATCHES/WARNINGS/ADVISORIES...
NONE.
&&

$$

000
FXUS63 KILX 041538
AFDILX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LINCOLN IL
1038 AM CDT SAT SEP 4 2010

.DISCUSSION...
ISSUED 1038 AM CDT SAT SEP 4 2010

SUNNY AND COOL CONDITIONS PREVAIL ACROSS CENTRAL ILLINOIS THIS
MORNING...WITH 15Z TEMPS RANGING FROM THE LOWER 60S NORTH TO
AROUND 70 DEGREES FAR SOUTHEAST. CU-RULE INDICATES FEW-SCT CU
DEVELOPING TODAY AND LATEST SATELLITE IMAGERY SUPPORTS THIS. HAVE
MADE SOME ADJUSTMENTS TO HOURLY TEMPS AND AFTERNOON HIGHS...MAINLY
TO INCREASE READINGS SOUTH OF I-70 BY A COUPLE OF DEGREES. CHANGES
ARE MINOR AND DO NOT REQUIRE A ZONE UPDATE AT THIS TIME.

BARNES
&&

.AVIATION...
ISSUED 655 AM CDT SAT SEP 4 2010

HIGH PRESSURE WILL BUILD INTO THE CENTRAL ILLINOIS TERMINAL AREA
DURING THE 12Z TAF VALID TIME. THIS FEATURE...AND THE ASSOCIATED
DRY AIRMASS...WILL KEEP THE WEATHER RATHER QUIET THROUGH THE
PERIOD. CLOUD COVER SHOULD BE NEGLIGIBLE...WITH ONLY SOME DIURNAL
CU DEVELOPING TODAY. WINDS ARE EXPECTED TO BE OUT OF THE NORTHWEST
INTO THIS EVENING...WITH SOME GUSTS AROUND 20 KTS LIKELY TODAY
DURING PEAK DIURNAL HEATING. AS THE HIGH PUSHES IN TONIGHT...AND
DIURNAL HEATING IS LOST...WINDS WILL FALL OFF AND BECOME VARIABLE.

BAK
&&

.PREV DISCUSSION...
ISSUED 330 AM CDT SAT SEP 4 2010

00Z MODELS ARE IN FAIR AGREEMENT THIS LABOR DAY WEEKEND ALONG
WITH MET AND MAV TEMPERATURE GUIDANCE. NOT TOO MANY CHANGES
PLANNED IN THIS FORECAST PACKAGE AS NICE WEATHER PREVAILS THROUGH
EARLY NEXT WEEK. BELOW NORMAL TEMPERATURES THIS WEEKEND GRADUALLY
MODIFY BACK ABOVE NORMAL MONDAY WITH BREEZY SSW FLOW AS HIGH
PRESSURE RIDGE DRIFTS EAST OF IL SUN/MON.

SHORT TERM...TODAY THROUGH MONDAY NIGHT.

STRONG LOW PRESSURE OF 992 MB OVER EASTERN ONTARIO ALONG WITH
STRONG 500 MB LOW OF 545 DM TO MOVE EAST WHILE 1022 MB HIGH
PRESSURE RIDGE OVER THE GREAT PLAINS DRIFTS EAST OVER IL TONIGHT.
HIGH PRESSURE THEN DRIFTS EAST OF IL SUNDAY AND INTO THE MID
ATLANTIC STATES SUNDAY NIGHT/MON. EXPECT MOSTLY SUNNY SKIES TODAY
WITH SCATTERED CUMULUS CLOUDS AND NW WINDS 10 TO 15 MPH AND GUSTS
UP TO 20-25 MPH THIS AFTERNOON ESPECIALLY FROM I-74 NE. HIGHS IN
THE LOWER 70S TODAY WITH AREAS FROM I-74 NE NEAR 70F. COOLEST DAY
IN CENTRAL IL SINCE MAY 21ST. TONIGHT WILL BE THE COOLEST NIGHT
WITH HIGH PRESSURE RIDGE NEARBY BRINGING CLEAR SKIES AND LIGHT
WINDS WITH LOWS IN THE MID TO UPPER 40S (COOLEST IN EAST CENTRAL IL).
MOSTLY SUNNY SKIES SUNDAY WITH MILDER HIGHS IN THE UPPER 70S TO
NEAR 80F SW AREAS.

MODELS BUILDING UPPER LEVEL RIDGE OVER THE OHIO VALLEY MONDAY
(LABOR DAY) WITH STRONG LOW PRESSURE 998 MB MOVING INTO THE UPPER
MS VALLEY. TIGHTENING PRESSURE GRADIENT OVER IL TO INCREASE SSW
WINDS ALONG WITH WARMER TEMPS IN THE MID 80S CENTRAL IL AND UPPER
80S SE IL. ADDED JUST A SLIGHT CHANCE OF A SHOWER OR THUNDERSTORM
LATER MONDAY NIGHT OVER THE IL RIVER VALLEY WITH A WEAKENING FRONTAL
BOUNDARY MOVING INTO NW IL AS STRONG LOW PRESSURE PASSES WELL
NORTH OF IL INTO NORTHERN WI.

LONG TERM...TUESDAY THROUGH FRIDAY.

WEAKENING FRONT MOVES SE THROUGH CENTRAL/SE IL TUE AND TOWARD THE
OHIO RIVER BY DAWN WED. BEST MOISTURE APPEARS SOUTH OF CENTRAL IL
WHILE BEST UPPER LEVEL DYNAMICS NORTH OVER THE GREAT LAKES. SO
JUST SLIGHT CHANCES OF SHOWERS AND THUNDERSTORMS AND BEST CHANCES
SOUTHERN AREAS. FRONT APPEARS TO MOVE BACK NORTH THU NIGHT AND FRI
AS UPPER LEVEL RIDGE BUILDS BACK INTO THE MS VALLEY RETURNING
WARMER WX.

HUETTL

&&

.ILX WATCHES/WARNINGS/ADVISORIES...
NONE.
&&

$$

000
FXUS63 KLOT 041511
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
1011 AM CDT SAT SEP 4 2010

.DISCUSSION...
330 AM CDT

FORECAST FOCUS CONTINUES TO CENTER ON A FAIRLY ACTIVE PATTERN IN
TERMS OF FRONTAL PROGRESSIONS ANTICIPATED FOR THE UPCOMING
WEEK...ALTHOUGH PRECIPITATION CHANCES WILL BE SOMEWHAT LIMITED WITH
MOISTURE AVAILABILITY QUESTIONS.

WATER VAPOR IMAGERY EARLY THIS MORNING INDICATING UPPER LOW SPINNING
ACROSS FAR SOUTHERN ONTARIO WITH CHANNELED UPPER LEVEL VORT DIGGING
THROUGH BASE OF THIS TROUGH ACROSS THE MID/UPPER MS RIVER VALLEY IN
ASSOCIATION WITH THE UPPER LEVEL JET. SURFACE OBS AND RADAR
IMAGERY HAVE INDICATED BRIEF PERIODS OF SPRINKLES OVER PAST FEW
HOURS LIKELY IN ASSOCIATION WITH WEAK DPVA AND WEAK LOW LEVEL
FRONTOGENESIS. LOW LEVEL COLD ADVECTION ASSOCIATED WITH THIS
BAROCLINIC ZONE WILL USHER IN EVEN COOLER TEMPS THAN
YESTERDAY...ALTHOUGH PLENTY OF INSOLATION AND DEEPER MIXING MAY
PARTIALLY OFFSET THE COOLER LOW LEVEL TEMPERATURES TODAY. TAKING
THE ABOVE INTO CONSIDERATION...HAVE GENERALLY MAINTAINED IDEA OF
TEMPERATURES A FEW DEGREES COOLER TODAY THAN YESTERDAY...IN THE
MID TO UPPER 60S. IN TERMS OF SKY COVER...THE PATCHY STRATOCU
EXTENDING FROM NORTH CENTRAL ILLINOIS INTO THE CHICAGO METRO AREA
SHOULD CONTINUE TO SHIFT EAST/SOUTHEAST THIS MORNING...AND WILL
BE REPLACED BY SOME DIURNAL FLAT CU DEVELOPMENT. SOME LIGHT LAKE
EFFECT RAIN SHOWERS WILL LIKELY REMAIN JUST TO THE EAST/NORTHEAST
OF PORTER COUNTY INDIANA...ESPECIALLY CONSIDERING LOW LEVEL WINDS
SHOULD BEGIN TO BACK THIS MORNING AS A LOW LEVEL RIDGE SINKS
SOUTHEASTWARD INTO THE MID MS RIVER VALLEY.

TEMPERATURE ADVECTION TO BECOME MORE NEUTRAL TONIGHT...ALTHOUGH A
BETTER CHANCE FOR COOLISH LOWS IN THE MID 40S IN STORE FOR TONIGHT
GIVEN GREATER DECOUPLING POTENTIAL GIVEN PROXIMITY OF SFC RIDGE
AXIS. WOULD SUSPECT THAT SOME OF THE FAVORED LOW LYING COOL SPOTS
MAY EVEN FLIRT WITH 40 DEGREES FOR MINS TONIGHT.

ON SUNDAY...SFC LOW IS EXPECTED TO DEEPEN ACROSS THE CENTRAL HIGH
PLAINS AS NEXT SIGNIFICANT UPPER LEVEL TROUGH MOVES ACROSS NWRN
CONUS. THE LOW LEVEL RIDGE SETTLING INTO LOWER/MID MS RIVER VALLEY
OVER NEXT 24 HOURS WILL LIMIT MOISTURE RETURN INITIALLY IN ADVANCE
OF THIS TROUGH. GIVEN INCREASING UNCERTAINTY OF LOW LEVEL
MOISTURE AVAILABILITY...DID GO AHEAD AND PULL THE SLIGHT CHANCE
POPS FOR RAIN SHOWERS SUNDAY AFTERNOON. BY SUNDAY
EVENING...ISENTROPIC LIFT SHOULD BEGIN TO STRENGTHEN MORE
SUBSTANTIALLY WITH SOME BETTER MID LEVEL LAPSE RATES DEVELOPING.
AT THIS POINT...WOULD SUSPECT THAT THE BEST CHANCE OF ELEVATED
SHOWERS/STORMS WOULD BE JUST NORTH OF FORECAST AREA ACROSS WI AND
INTO THE UPPER GREAT LAKES AS ZONE OF STRONGER ISENTROPIC ASCENT
LIFTS NORTHWARD WITH THE WARM FRONTAL-LIKE FEATURE. THIS ALSO
APPEARS TO BE A MORE SYNOPTICALLY FAVORED REGION FOR LARGE SCALE
ASCENT WITH WEAK UPPER JET STREAK COUPLING NOTED IN NAM/GFS SOLUTIONS.

LOW/MID LEVELS SHOULD DRY OUT BY EARLY MONDAY AS LOW LEVEL WARM
FRONTS LIFTS THROUGH NORTHERN GREAT LAKES AND THUS DRY CONDITIONS
EXPECTED TO CONTINUE THROUGH THE DAY MONDAY. UPPER DYNAMICS
ASSOCIATED WITH THE AFOREMENTIONED UPPER TROUGH WILL BEGIN TO
INCREASE BY MONDAY NIGHT...BUT ESPECIALLY AGAIN TO THE NORTH OF
THE AREA. THUS...WILL HANDLE MONDAY NIGHT PERIOD WITH JUST SLIGHT
CHANCE POPS FOR TSRA. TEMPERATURES ON MONDAY IN THE WARM SECTOR
SHOULD SHOOT BACK UP INTO THE LOWER TO MID 80S ACROSS MUCH OF THE
AREA...AND WITH THIS WARMING AND INITIALLY DRY LOW LEVELS COMES
SOME CONCERN FOR FIRE WEATHER...WHICH IS HIGHLIGHTED BELOW.

SYSTEM WILL OCCLUDE ACROSS UPPER MIDWEST TUESDAY WITH COLD FRONT
EXPECTED TO STALL OUT ACROSS OR JUST THE SOUTH OF THE AREA...AND
THEN BEGIN TO RETURN NORTHWARD AS A WARM FRONT AGAIN TOWARD THE END
OF THE WEEK. THIS RETURN WARM/MOIST ADVECTION COULD BE CONDUCIVE FOR
SOME SCT SHOWERS/STORMS BY THURS. HOWEVER...MEDIUM RANGE MODELS
DIVERGE TO A LARGER DEGREE WITH NEXT SHORT WAVE TROUGH FOR
THURS/FRI WITH ECMWF A SIGNIFICANTLY SLOWER SOLUTION COMPARED TO
GFS/NCEP ENSEMBLES. CONFIDENCE IN TIMING PRECIP CHANCES IS LOW AT
THIS TIME...SO DID NOT CHANGE LOW CHANCE POPS THURS/FRI...WITH SOME
HIGHER CONFIDENCE IN AT LEAST A SHIFT BACK TO WARMER TEMPS AGAIN
TOWARD THE END OF THE PERIOD.

MARSILI

&&

.FIRE WEATHER...
330 AM CDT

ON MONDAY...SOUTH WINDS ARE EXPECTED TO INCREASE INTO THE 15 TO 25
MPH RANGE WITH SOME GUSTS TO 30 MPH OR SLIGHTLY HIGHER. THERE IS A
POSSIBILITY THAT SOME DRIER LOW LEVEL AIR MAY MIX DOWN TO THE
SURFACE WHICH WOULD RESULT IN MINIMUM AFTERNOON RELATIVE
HUMIDITIES AROUND OR LESS THAN 30 PERCENT. CONFIDENCE IN MEETING
RED FLAG CONDITIONS IS LOW AT THIS POINT GIVEN UNCERTAINTY AS TO
HOW MUCH OF THIS LOW LEVEL DRY AIR WILL MIX TO THE SURFACE...AND
ALSO 10 HR FUEL MOISTURES ARE STILL RUNNING ON THE HIGH SIDE
ACROSS THE AREA.

MARSILI

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 15Z...

A WIND WITH A DIRECTION OF 280 TO 300 DEGREES WILL CONTINUE THIS
LATE MORNING AND EARLY AFTERNOON. THE SPEED IS EXPECTED TO BE
AROUND 14 KNOTS WITH GUSTS TO 20 KNOTS. VFR CONDITIONS WILL
CONTINUE WITH SCATTERED CLOUDS 2500 TO 3000 FEET.

//DISCUSSION...UPDATED 12Z...

MAINLY CLEAR SKIES SHOULD GIVE WAY TO DEVELOPING CUMULUS/STRATOCU
DECK BY MID-LATE MORNING AS LOW LEVEL LAPSE RATES STEEPEN UP. ALSO
ANTICIPATE WINDS TO PICK WITH GUSTS TO AROUND 20KT LATE THIS
MORNING WITH GUSTINESS LASTING UNTIL SUNSET...AT WHICH TIME THE
WINDS WILL QUICKLY DIMINISH AND BEGIN TO GRADUALLY BACK TO WEST
THEN SOUTHWEST BY SUNDAY MORNING. SUNSET SHOULD ALSO PUT AN END TO
THE DIURNALLY DRIVEN CUMULUS WITH SKIES EXPECTED TO BECOME SKC.

//ORD AND MDW CONFIDENCE...UPDATED 15Z...

HIGH CONFIDENCE IN THE WIND AND CLOUDS.

//OUTLOOK FOR ORD/MDW FOR 18Z SUNDAY-12Z THURSDAY...UPDATED 06Z...

SUNDAY...SLIGHT CHC -SHRA SUN NIGHT...OTHERWISE VFR.
MONDAY...VFR. STRONG/GUSTY SOUTH WINDS LATE MORNING INTO AFTERNOON.
TUESDAY AND WEDNESDAY...VFR.
THURSDAY...SLIGHT CHC TSRA...OTHERWISE VFR.

&&

.MARINE...
215 AM CDT

SEEING SIGNS OF THE PRESSURE GRADIENT AND WINDS STARTING TO SLOWLY
EASE OVER THE LAKE...WITH NO GALE FORCE GUSTS FOR THE PAST COUPLE
HOURS AT THE SOUTH BUOY AND WINDS DOWN A BIT NORTH BUOY. STILL
SEEING GUSTS TO AROUND GALE FORCE AT SOME OF THE COASTAL OB SITES
ALONG THE EASTERN SHORES...SO PLAN TO HANG ONTO THE GL.W UNTIL MID
MORNING SOUTH. FARTHER NORTH GRADIENT MAY BE A BIT SLOWER TO RELAX
AND WILL HANG ONTO GALES THERE INTO THE EARLY AFTERNOON. WINDS RELAX
FURTHER TONIGHT INTO SUNDAY AS THEY GRADUALLY BACK TO A MORE
SOUTHERLY DIRECTION AS HIGH MOVES EAST INTO THE OHIO VALLEY AND THE
NEXT LOW DEVELOPS OVER THE PLAINS.

SOUTHERLY GRADIENT WILL TIGHTEN UP CONSIDERABLY MONDAY INTO MONDAY
NIGHT AS LOW TRACKS FROM THE CENTRAL PLAINS INTO THE UPPER GREAT
LAKES. MODELS CONTINUE TO SUGGEST THAT WE COULD BE LOOKING AT
SOUTHERLY GALES DURING THIS TIME RANGE OVER SOUTHERN 1/2 TO 2/3 OF
THE LAKE...AND THEN SOUTHWEST GALES OVER NORTHERN LAKE MICHIGAN MON
NIGHT INTO TUES AS THE LOW PULLS OUT AND SLOWLY WEAKENS. BUT MODELS
ARE ALSO SHOWING THE BOUNDARY LAYER REMAINING WELL MIXED OVER THE
LAKE...WHICH MAY NOT BE THE CASE.  COLD AIR ADVECTION AND UPWELLING
FROM THE LARGE WAVES THIS WEEKEND MAY KNOCK DOWN WATER TEMPS LEADING
TO MORE STABLE CONDITIONS OVER THE LAKE THAN MODEL SOUNDINGS
SUGGEST...SO HAVE OPTED TO STICK WITH JUST 30KT WINDS FOR NOW AND
RE-ACCESS THINGS OVER THE WEEKEND BEFORE BUMPING UP WINDS TO GALES.

FOR THE NEARSHORE WILL BE KILLING THE GALE WARNING WITH THIS
MORNING`S ISSUANCE AND REPLACING WITH A SMALL CRAFT ADV THRU THE
AFTERNOON FOR THE ILLINOIS SHORE WHERE WAVES OUT TOWARD THE 5 MILE
OFF SHORE RANGE MAY STILL BE NEAR CRITERIA AND WHERE GUSTS COULD
GET UP TO AROUND CRITERIA AS WELL. FOR THE INDIANA SHORE WHERE THE
FETCH IS LONGER PLAN TO HANG ONTO THE ADV THRU TONIGHT TO GIVE THE
WAVES TIME TO FULLY SUBSIDE.

IZZI

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...GALE WARNING...LMZ261-LMZ362-LMZ364-LMZ563 UNTIL 3 PM SATURDAY.

     SMALL CRAFT ADVISORY...INDIANA NEARSHORE WATERS UNTIL 4 AM SUNDAY.

     SMALL CRAFT ADVISORY...ILLINOIS NEARSHORE WATERS UNTIL 4 PM SATURDAY.

&&

$$

000
FXUS63 KILX 041155
AFDILX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LINCOLN IL
655 AM CDT SAT SEP 4 2010

.DISCUSSION...
ISSUED 330 AM CDT SAT SEP 4 2010

00Z MODELS ARE IN FAIR AGREEMENT THIS LABOR DAY WEEKEND ALONG
WITH MET AND MAV TEMPERATURE GUIDANCE. NOT TOO MANY CHANGES
PLANNED IN THIS FORECAST PACKAGE AS NICE WEATHER PREVAILS THROUGH
EARLY NEXT WEEK. BELOW NORMAL TEMPERATURES THIS WEEKEND GRADUALLY
MODIFY BACK ABOVE NORMAL MONDAY WITH BREEZY SSW FLOW AS HIGH
PRESSURE RIDGE DRIFTS EAST OF IL SUN/MON.

SHORT TERM...TODAY THROUGH MONDAY NIGHT.

STRONG LOW PRESSURE OF 992 MB OVER EASTERN ONTARIO ALONG WITH
STRONG 500 MB LOW OF 545 DM TO MOVE EAST WHILE 1022 MB HIGH
PRESSURE RIDGE OVER THE GREAT PLAINS DRIFTS EAST OVER IL TONIGHT.
HIGH PRESSURE THEN DRIFTS EAST OF IL SUNDAY AND INTO THE MID
ATLANTIC STATES SUNDAY NIGHT/MON. EXPECT MOSTLY SUNNY SKIES TODAY
WITH SCATTERED CUMULUS CLOUDS AND NW WINDS 10 TO 15 MPH AND GUSTS
UP TO 20-25 MPH THIS AFTERNOON ESPECIALLY FROM I-74 NE. HIGHS IN
THE LOWER 70S TODAY WITH AREAS FROM I-74 NE NEAR 70F. COOLEST DAY
IN CENTRAL IL SINCE MAY 21ST. TONIGHT WILL BE THE COOLEST NIGHT
WITH HIGH PRESSURE RIDGE NEARBY BRINGING CLEAR SKIES AND LIGHT
WINDS WITH LOWS IN THE MID TO UPPER 40S (COOLEST IN EAST CENTRAL IL).
MOSTLY SUNNY SKIES SUNDAY WITH MILDER HIGHS IN THE UPPER 70S TO
NEAR 80F SW AREAS.

MODELS BUILDING UPPER LEVEL RIDGE OVER THE OHIO VALLEY MONDAY
(LABOR DAY) WITH STRONG LOW PRESSURE 998 MB MOVING INTO THE UPPER
MS VALLEY. TIGHTENING PRESSURE GRADIENT OVER IL TO INCREASE SSW
WINDS ALONG WITH WARMER TEMPS IN THE MID 80S CENTRAL IL AND UPPER
80S SE IL. ADDED JUST A SLIGHT CHANCE OF A SHOWER OR THUNDERSTORM
LATER MONDAY NIGHT OVER THE IL RIVER VALLEY WITH A WEAKENING FRONTAL
BOUNDARY MOVING INTO NW IL AS STRONG LOW PRESSURE PASSES WELL
NORTH OF IL INTO NORTHERN WI.

LONG TERM...TUESDAY THROUGH FRIDAY.

WEAKENING FRONT MOVES SE THROUGH CENTRAL/SE IL TUE AND TOWARD THE
OHIO RIVER BY DAWN WED. BEST MOISTURE APPEARS SOUTH OF CENTRAL IL
WHILE BEST UPPER LEVEL DYNAMICS NORTH OVER THE GREAT LAKES. SO
JUST SLIGHT CHANCES OF SHOWERS AND THUNDERSTORMS AND BEST CHANCES
SOUTHERN AREAS. FRONT APPEARS TO MOVE BACK NORTH THU NIGHT AND FRI
AS UPPER LEVEL RIDGE BUILDS BACK INTO THE MS VALLEY RETURNING
WARMER WX.

HUETTL
&&

.AVIATION...
ISSUED 655 AM CDT SAT SEP 4 2010

HIGH PRESSURE WILL BUILD INTO THE CENTRAL ILLINOIS TERMINAL AREA
DURING THE 12Z TAF VALID TIME. THIS FEATURE...AND THE ASSOCIATED
DRY AIRMASS...WILL KEEP THE WEATHER RATHER QUIET THROUGH THE
PERIOD. CLOUD COVER SHOULD BE NEGLIGIBLE...WITH ONLY SOME DIURNAL
CU DEVELOPING TODAY. WINDS ARE EXPECTED TO BE OUT OF THE NORTHWEST
INTO THIS EVENING...WITH SOME GUSTS AROUND 20 KTS LIKELY TODAY
DURING PEAK DIURNAL HEATING. AS THE HIGH PUSHES IN TONIGHT...AND
DIURNAL HEATING IS LOST...WINDS WILL FALL OFF AND BECOME VARIABLE.

BAK
&&

.ILX WATCHES/WARNINGS/ADVISORIES...
NONE.
&&

$$

000
FXUS63 KLOT 041100
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
600 AM CDT SAT SEP 4 2010

.DISCUSSION...
330 AM CDT

FORECAST FOCUS CONTINUES TO CENTER ON A FAIRLY ACTIVE PATTERN IN
TERMS OF FRONTAL PROGRESSIONS ANTICIPATED FOR THE UPCOMING
WEEK...ALTHOUGH PRECIPITATION CHANCES WILL BE SOMEWHAT LIMITED WITH
MOISTURE AVAILABILITY QUESTIONS.

WATER VAPOR IMAGERY EARLY THIS MORNING INDICATING UPPER LOW SPINNING
ACROSS FAR SOUTHERN ONTARIO WITH CHANNELED UPPER LEVEL VORT DIGGING
THROUGH BASE OF THIS TROUGH ACROSS THE MID/UPPER MS RIVER VALLEY IN
ASSOCIATION WITH THE UPPER LEVEL JET. SURFACE OBS AND RADAR
IMAGERY HAVE INDICATED BRIEF PERIODS OF SPRINKLES OVER PAST FEW
HOURS LIKELY IN ASSOCIATION WITH WEAK DPVA AND WEAK LOW LEVEL
FRONTOGENESIS. LOW LEVEL COLD ADVECTION ASSOCIATED WITH THIS
BAROCLINIC ZONE WILL USHER IN EVEN COOLER TEMPS THAN
YESTERDAY...ALTHOUGH PLENTY OF INSOLATION AND DEEPER MIXING MAY
PARTIALLY OFFSET THE COOLER LOW LEVEL TEMPERATURES TODAY. TAKING
THE ABOVE INTO CONSIDERATION...HAVE GENERALLY MAINTAINED IDEA OF
TEMPERATURES A FEW DEGREES COOLER TODAY THAN YESTERDAY...IN THE
MID TO UPPER 60S. IN TERMS OF SKY COVER...THE PATCHY STRATOCU
EXTENDING FROM NORTH CENTRAL ILLINOIS INTO THE CHICAGO METRO AREA
SHOULD CONTINUE TO SHIFT EAST/SOUTHEAST THIS MORNING...AND WILL
BE REPLACED BY SOME DIURNAL FLAT CU DEVELOPMENT. SOME LIGHT LAKE
EFFECT RAIN SHOWERS WILL LIKELY REMAIN JUST TO THE EAST/NORTHEAST
OF PORTER COUNTY INDIANA...ESPECIALLY CONSIDERING LOW LEVEL WINDS
SHOULD BEGIN TO BACK THIS MORNING AS A LOW LEVEL RIDGE SINKS
SOUTHEASTWARD INTO THE MID MS RIVER VALLEY.

TEMPERATURE ADVECTION TO BECOME MORE NEUTRAL TONIGHT...ALTHOUGH A
BETTER CHANCE FOR COOLISH LOWS IN THE MID 40S IN STORE FOR TONIGHT
GIVEN GREATER DECOUPLING POTENTIAL GIVEN PROXIMITY OF SFC RIDGE
AXIS. WOULD SUSPECT THAT SOME OF THE FAVORED LOW LYING COOL SPOTS
MAY EVEN FLIRT WITH 40 DEGREES FOR MINS TONIGHT.

ON SUNDAY...SFC LOW IS EXPECTED TO DEEPEN ACROSS THE CENTRAL HIGH
PLAINS AS NEXT SIGNIFICANT UPPER LEVEL TROUGH MOVES ACROSS NWRN
CONUS. THE LOW LEVEL RIDGE SETTLING INTO LOWER/MID MS RIVER VALLEY
OVER NEXT 24 HOURS WILL LIMIT MOISTURE RETURN INITIALLY IN ADVANCE
OF THIS TROUGH. GIVEN INCREASING UNCERTAINTY OF LOW LEVEL
MOISTURE AVAILABILITY...DID GO AHEAD AND PULL THE SLIGHT CHANCE
POPS FOR RAIN SHOWERS SUNDAY AFTERNOON. BY SUNDAY
EVENING...ISENTROPIC LIFT SHOULD BEGIN TO STRENGTHEN MORE
SUBSTANTIALLY WITH SOME BETTER MID LEVEL LAPSE RATES DEVELOPING.
AT THIS POINT...WOULD SUSPECT THAT THE BEST CHANCE OF ELEVATED
SHOWERS/STORMS WOULD BE JUST NORTH OF FORECAST AREA ACROSS WI AND
INTO THE UPPER GREAT LAKES AS ZONE OF STRONGER ISENTROPIC ASCENT
LIFTS NORTHWARD WITH THE WARM FRONTAL-LIKE FEATURE. THIS ALSO
APPEARS TO BE A MORE SYNOPTICALLY FAVORED REGION FOR LARGE SCALE
ASCENT WITH WEAK UPPER JET STREAK COUPLING NOTED IN NAM/GFS SOLUTIONS.

LOW/MID LEVELS SHOULD DRY OUT BY EARLY MONDAY AS LOW LEVEL WARM
FRONTS LIFTS THROUGH NORTHERN GREAT LAKES AND THUS DRY CONDITIONS
EXPECTED TO CONTINUE THROUGH THE DAY MONDAY. UPPER DYNAMICS
ASSOCIATED WITH THE AFOREMENTIONED UPPER TROUGH WILL BEGIN TO
INCREASE BY MONDAY NIGHT...BUT ESPECIALLY AGAIN TO THE NORTH OF
THE AREA. THUS...WILL HANDLE MONDAY NIGHT PERIOD WITH JUST SLIGHT
CHANCE POPS FOR TSRA. TEMPERATURES ON MONDAY IN THE WARM SECTOR
SHOULD SHOOT BACK UP INTO THE LOWER TO MID 80S ACROSS MUCH OF THE
AREA...AND WITH THIS WARMING AND INITIALLY DRY LOW LEVELS COMES
SOME CONCERN FOR FIRE WEATHER...WHICH IS HIGHLIGHTED BELOW.

SYSTEM WILL OCCLUDE ACROSS UPPER MIDWEST TUESDAY WITH COLD FRONT
EXPECTED TO STALL OUT ACROSS OR JUST THE SOUTH OF THE AREA...AND
THEN BEGIN TO RETURN NORTHWARD AS A WARM FRONT AGAIN TOWARD THE END
OF THE WEEK. THIS RETURN WARM/MOIST ADVECTION COULD BE CONDUCIVE FOR
SOME SCT SHOWERS/STORMS BY THURS. HOWEVER...MEDIUM RANGE MODELS
DIVERGE TO A LARGER DEGREE WITH NEXT SHORT WAVE TROUGH FOR
THURS/FRI WITH ECMWF A SIGNIFICANTLY SLOWER SOLUTION COMPARED TO
GFS/NCEP ENSEMBLES. CONFIDENCE IN TIMING PRECIP CHANCES IS LOW AT
THIS TIME...SO DID NOT CHANGE LOW CHANCE POPS THURS/FRI...WITH SOME
HIGHER CONFIDENCE IN AT LEAST A SHIFT BACK TO WARMER TEMPS AGAIN
TOWARD THE END OF THE PERIOD.

MARSILI

&&

.FIRE WEATHER...
330 AM CDT

ON MONDAY...SOUTH WINDS ARE EXPECTED TO INCREASE INTO THE 15 TO 25
MPH RANGE WITH SOME GUSTS TO 30 MPH OR SLIGHTLY HIGHER. THERE IS A
POSSIBILITY THAT SOME DRIER LOW LEVEL AIR MAY MIX DOWN TO THE
SURFACE WHICH WOULD RESULT IN MINIMUM AFTERNOON RELATIVE
HUMIDITIES AROUND OR LESS THAN 30 PERCENT. CONFIDENCE IN MEETING
RED FLAG CONDITIONS IS LOW AT THIS POINT GIVEN UNCERTAINTY AS TO
HOW MUCH OF THIS LOW LEVEL DRY AIR WILL MIX TO THE SURFACE...AND
ALSO 10 HR FUEL MOISTURES ARE STILL RUNNING ON THE HIGH SIDE
ACROSS THE AREA.

MARSILI

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 12Z...

MODERATELY GUSTY NW WINDS TODAY...BUT NOT ANTICIPATING ANY
ADVERSE IMPACTS TO OPERATIONS DUE TO WEATHER.

IZZI

//DISCUSSION...UPDATED 12Z...

MAINLY CLEAR SKIES SHOULD GIVE WAY TO DEVELOPING CUMULUS/STRATOCU
DECK BY MID-LATE MORNING AS LOW LEVEL LAPSE RATES STEEPEN UP. ALSO
ANTICIPATE WINDS TO PICK WITH GUSTS TO AROUND 20KT LATE THIS
MORNING WITH GUSTINESS LASTING UNTIL SUNSET...AT WHICH TIME THE
WINDS WILL QUICLY DIMINISH AND BEGIN TO GRADUALLY BACK TO WEST
THEN SOUTHWEST BY SUNDAY MORNING. SUNSET SHOULD ALSO PUT AN END TO
THE DIURNALLY DRIVEN CUMULUS WITH SKIES EXPECTED TO BECOME SKC.

IZZI

//ORD AND MDW CONFIDENCE...UPDATED 12Z...

HIGH CONFIDENCE IN ALL ASPECTS OF THE FORECAST.

IZZI

//OUTLOOK FOR ORD/MDW FOR 18Z SUNDAY-12Z THURSDAY...UPDATED 06Z...

SUNDAY...SLIGHT CHC -SHRA SUN NIGHT...OTHERWISE VFR.
MONDAY...VFR. STRONG/GUSTY SOUTH WINDS LATE MORNING INTO AFTERNOON.
TUESDAY AND WEDNESDAY...VFR.
THURSDAY...SLIGHT CHC TSRA...OTHERWISE VFR.

IZZI

&&

.MARINE...
215 AM CDT

SEEING SIGNS OF THE PRESSURE GRADIENT AND WINDS STARTING TO SLOWLY
EASE OVER THE LAKE...WITH NO GALE FORCE GUSTS FOR THE PAST COUPLE
HOURS AT THE SOUTH BUOY AND WINDS DOWN A BIT NORTH BUOY. STILL
SEEING GUSTS TO AROUND GALE FORCE AT SOME OF THE COASTAL OB SITES
ALONG THE EASTERN SHORES...SO PLAN TO HANG ONTO THE GL.W UNTIL MID
MORNING SOUTH. FARTHER NORTH GRADIENT MAY BE A BIT SLOWER TO RELAX
AND WILL HANG ONTO GALES THERE INTO THE EARLY AFTERNOON. WINDS RELAX
FURTHER TONIGHT INTO SUNDAY AS THEY GRADUALLY BACK TO A MORE
SOUTHERLY DIRECTION AS HIGH MOVES EAST INTO THE OHIO VALLEY AND THE
NEXT LOW DEVELOPS OVER THE PLAINS.

SOUTHERLY GRADIENT WILL TIGHTEN UP CONSIDERABLY MONDAY INTO MONDAY
NIGHT AS LOW TRACKS FROM THE CENTRAL PLAINS INTO THE UPPER GREAT
LAKES. MODELS CONTINUE TO SUGGEST THAT WE COULD BE LOOKING AT
SOUTHERLY GALES DURING THIS TIME RANGE OVER SOUTHERN 1/2 TO 2/3 OF
THE LAKE...AND THEN SOUTHWEST GALES OVER NORTHERN LAKE MICHIGAN MON
NIGHT INTO TUES AS THE LOW PULLS OUT AND SLOWLY WEAKENS. BUT MODELS
ARE ALSO SHOWING THE BOUNDARY LAYER REMAINING WELL MIXED OVER THE
LAKE...WHICH MAY NOT BE THE CASE.  COLD AIR ADVECTION AND UPWELLING
FROM THE LARGE WAVES THIS WEEKEND MAY KNOCK DOWN WATER TEMPS LEADING
TO MORE STABLE CONDITIONS OVER THE LAKE THAN MODEL SOUNDINGS
SUGGEST...SO HAVE OPTED TO STICK WITH JUST 30KT WINDS FOR NOW AND
RE-ACCESS THINGS OVER THE WEEKEND BEFORE BUMPING UP WINDS TO GALES.

FOR THE NEARSHORE WILL BE KILLING THE GALE WARNING WITH THIS
MORNING`S ISSUANCE AND REPLACING WITH A SMALL CRAFT ADV THRU THE
AFTERNOON FOR THE ILLINOIS SHORE WHERE WAVES OUT TOWARD THE 5 MILE
OFF SHORE RANGE MAY STILL BE NEAR CRITERIA AND WHERE GUSTS COULD
GET UP TO AROUND CRITERIA AS WELL. FOR THE INDIANA SHORE WHERE THE
FETCH IS LONGER PLAN TO HANG ONTO THE ADV THRU TONIGHT TO GIVE THE
WAVES TIME TO FULLY SUBSIDE.

IZZI

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...GALE WARNING...LMZ080-LMZ366-LMZ565-LMZ567-LMZ669-LMZ671-LMZ673-
     LMZ675-LMZ777-LMZ779-LMZ868-LMZ870-LMZ872-LMZ874-LMZ876-
     LMZ878 UNTIL 9 AM SATURDAY.

     GALE WARNING...LMZ261-LMZ362-LMZ364-LMZ563 UNTIL 3 PM SATURDAY.

     SMALL CRAFT ADVISORY...INDIANA NEARSHORE WATERS UNTIL 4 AM SUNDAY.

     SMALL CRAFT ADVISORY...ILLINOIS NEARSHORE WATERS UNTIL 4 PM SATURDAY.

&&

$$

000
FXUS63 KLOT 040908
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
408 AM CDT SAT SEP 4 2010

.DISCUSSION...
330 AM CDT

FORECAST FOCUS CONTINUES TO CENTER ON A FAIRLY ACTIVE PATTERN IN
TERMS OF FRONTAL PROGRESSIONS ANTICIPATED FOR THE UPCOMING
WEEK...ALTHOUGH PRECIPITATION CHANCES WILL BE SOMEWHAT LIMITED WITH
MOISTURE AVAILABILITY QUESTIONS.

WATER VAPOR IMAGERY EARLY THIS MORNING INDICATING UPPER LOW SPINNING
ACROSS FAR SOUTHERN ONTARIO WITH CHANNELED UPPER LEVEL VORT DIGGING
THROUGH BASE OF THIS TROUGH ACROSS THE MID/UPPER MS RIVER VALLEY IN
ASSOCIATION WITH THE UPPER LEVEL JET. SURFACE OBS AND RADAR
IMAGERY HAVE INDICATED BRIEF PERIODS OF SPRINKLES OVER PAST FEW
HOURS LIKELY IN ASSOCIATION WITH WEAK DPVA AND WEAK LOW LEVEL
FRONTOGENESIS. LOW LEVEL COLD ADVECTION ASSOCIATED WITH THIS
BAROCLINIC ZONE WILL USHER IN EVEN COOLER TEMPS THAN
YESTERDAY...ALTHOUGH PLENTY OF INSOLATION AND DEEPER MIXING MAY
PARTIALLY OFFSET THE COOLER LOW LEVEL TEMPERATURES TODAY. TAKING
THE ABOVE INTO CONSIDERATION...HAVE GENERALLY MAINTAINED IDEA OF
TEMPERATURES A FEW DEGREES COOLER TODAY THAN YESTERDAY...IN THE
MID TO UPPER 60S. IN TERMS OF SKY COVER...THE PATCHY STRATOCU
EXTENDING FROM NORTH CENTRAL ILLINOIS INTO THE CHICAGO METRO AREA
SHOULD CONTINUE TO SHIFT EAST/SOUTHEAST THIS MORNING...AND WILL
BE REPLACED BY SOME DIURNAL FLAT CU DEVELOPMENT. SOME LIGHT LAKE
EFFECT RAIN SHOWERS WILL LIKELY REMAIN JUST TO THE EAST/NORTHEAST
OF PORTER COUNTY INDIANA...ESPECIALLY CONSIDERING LOW LEVEL WINDS
SHOULD BEGIN TO BACK THIS MORNING AS A LOW LEVEL RIDGE SINKS
SOUTHEASTWARD INTO THE MID MS RIVER VALLEY.

TEMPERATURE ADVECTION TO BECOME MORE NEUTRAL TONIGHT...ALTHOUGH A
BETTER CHANCE FOR COOLISH LOWS IN THE MID 40S IN STORE FOR TONIGHT
GIVEN GREATER DECOUPLING POTENTIAL GIVEN PROXIMITY OF SFC RIDGE
AXIS. WOULD SUSPECT THAT SOME OF THE FAVORED LOW LYING COOL SPOTS
MAY EVEN FLIRT WITH 40 DEGREES FOR MINS TONIGHT.

ON SUNDAY...SFC LOW IS EXPECTED TO DEEPEN ACROSS THE CENTRAL HIGH
PLAINS AS NEXT SIGNIFICANT UPPER LEVEL TROUGH MOVES ACROSS NWRN
CONUS. THE LOW LEVEL RIDGE SETTLING INTO LOWER/MID MS RIVER VALLEY
OVER NEXT 24 HOURS WILL LIMIT MOISTURE RETURN INITIALLY IN ADVANCE
OF THIS TROUGH. GIVEN INCREASING UNCERTAINTY OF LOW LEVEL
MOISTURE AVAILABILITY...DID GO AHEAD AND PULL THE SLIGHT CHANCE
POPS FOR RAIN SHOWERS SUNDAY AFTERNOON. BY SUNDAY
EVENING...ISENTROPIC LIFT SHOULD BEGIN TO STRENGTHEN MORE
SUBSTANTIALLY WITH SOME BETTER MID LEVEL LAPSE RATES DEVELOPING.
AT THIS POINT...WOULD SUSPECT THAT THE BEST CHANCE OF ELEVATED
SHOWERS/STORMS WOULD BE JUST NORTH OF FORECAST AREA ACROSS WI AND
INTO THE UPPER GREAT LAKES AS ZONE OF STRONGER ISENTROPIC ASCENT
LIFTS NORTHWARD WITH THE WARM FRONTAL-LIKE FEATURE. THIS ALSO
APPEARS TO BE A MORE SYNOPTICALLY FAVORED REGION FOR LARGE SCALE
ASCENT WITH WEAK UPPER JET STREAK COUPLING NOTED IN NAM/GFS SOLUTIONS.

LOW/MID LEVELS SHOULD DRY OUT BY EARLY MONDAY AS LOW LEVEL WARM
FRONTS LIFTS THROUGH NORTHERN GREAT LAKES AND THUS DRY CONDITIONS
EXPECTED TO CONTINUE THROUGH THE DAY MONDAY. UPPER DYNAMICS
ASSOCIATED WITH THE AFOREMENTIONED UPPER TROUGH WILL BEGIN TO
INCREASE BY MONDAY NIGHT...BUT ESPECIALLY AGAIN TO THE NORTH OF
THE AREA. THUS...WILL HANDLE MONDAY NIGHT PERIOD WITH JUST SLIGHT
CHANCE POPS FOR TSRA. TEMPERATURES ON MONDAY IN THE WARM SECTOR
SHOULD SHOOT BACK UP INTO THE LOWER TO MID 80S ACROSS MUCH OF THE
AREA...AND WITH THIS WARMING AND INITIALLY DRY LOW LEVELS COMES
SOME CONCERN FOR FIRE WEATHER...WHICH IS HIGHLIGHTED BELOW.

SYSTEM WILL OCCLUDE ACROSS UPPER MIDWEST TUESDAY WITH COLD FRONT
EXPECTED TO STALL OUT ACROSS OR JUST THE SOUTH OF THE AREA...AND
THEN BEGIN TO RETURN NORTHWARD AS A WARM FRONT AGAIN TOWARD THE END
OF THE WEEK. THIS RETURN WARM/MOIST ADVECTION COULD BE CONDUCIVE FOR
SOME SCT SHOWERS/STORMS BY THURS. HOWEVER...MEDIUM RANGE MODELS
DIVERGE TO A LARGER DEGREE WITH NEXT SHORT WAVE TROUGH FOR
THURS/FRI WITH ECMWF A SIGNIFICANTLY SLOWER SOLUTION COMPARED TO
GFS/NCEP ENSEMBLES. CONFIDENCE IN TIMING PRECIP CHANCES IS LOW AT
THIS TIME...SO DID NOT CHANGE LOW CHANCE POPS THURS/FRI...WITH SOME
HIGHER CONFIDENCE IN AT LEAST A SHIFT BACK TO WARMER TEMPS AGAIN
TOWARD THE END OF THE PERIOD.

MARSILI

&&

.FIRE WEATHER...
330 AM CDT

ON MONDAY...SOUTH WINDS ARE EXPECTED TO INCREASE INTO THE 15 TO 25
MPH RANGE WITH SOME GUSTS TO 30 MPH OR SLIGHTLY HIGHER. THERE IS A
POSSIBILITY THAT SOME DRIER LOW LEVEL AIR MAY MIX DOWN TO THE
SURFACE WHICH WOULD RESULT IN MINIMUM AFTERNOON RELATIVE
HUMIDITIES AROUND OR LESS THAN 30 PERCENT. CONFIDENCE IN MEETING
RED FLAG CONDITIONS IS LOW AT THIS POINT GIVEN UNCERTAINTY AS TO
HOW MUCH OF THIS LOW LEVEL DRY AIR WILL MIX TO THE SURFACE...AND
ALSO 10 HR FUEL MOISTURES ARE STILL RUNNING ON THE HIGH SIDE
ACROSS THE AREA.

MARSILI

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 09Z...

MODERATELY GUSTY NW WINDS LIKELY TODAY. WEATHER IMPACT ON OPS
SHOULD BE NIL.

IZZI

//DISCUSSION...UPDATED 09Z...

LOW LEVELS WILL BE SOMEWHAT MIXED EARLY THIS MORNING WITH SOME
OCNL GUSTS UP TO AROUND 20KT. ISOLD -SHRA AND BKN VFR TO OCNL MVFR
DECK ARE MOVING SOUTH OF THE REGION LEAVING SKIES CLEAR FOR
NOW...BUT SHOULD SEE SCT TO BKN STRATOCU DECK BLOSSOM WITH DAYTIME
HEATING. AT LEAST MIXED SUNSHINE AND HEATING SATURDAY SHOULD
SUSTAIN GUSTS TO AROUND 20KT...EVEN THOUGH PRESSURE GRADIENT WILL
BE GRADUALLY RELAXING. EXPECT SCT-BKN STRATOCU TO FADE WITH
SUNSET SAT EVENING AND WINDS SHOULD ALSO RELAX WITH RIDGE AXIS
MOVING INTO THE REGION.

IZZI

//ORD AND MDW CONFIDENCE...UPDATED 09Z...

HIGH CONFIDENCE IN ALL ASPECTS OF THE FORECAST.

IZZI

//OUTLOOK FOR ORD/MDW FOR 12Z SUNDAY-12Z FRIDAY...UPDATED 06Z...

SUNDAY...SLIGHT CHC -SHRA SUN NIGHT...OTHERWISE VFR.
MONDAY...VFR. STRONG/GUSTY SOUTH WINDS LATE MORNING INTO AFTERNOON.
TUESDAY AND WEDNESDAY...VFR.
THURSDAY...SLIGHT CHC TSRA...OTHERWISE VFR.

IZZI

&&

.MARINE...
215 AM CDT

SEEING SIGNS OF THE PRESSURE GRADIENT AND WINDS STARTING TO SLOWLY
EASE OVER THE LAKE...WITH NO GALE FORCE GUSTS FOR THE PAST COUPLE
HOURS AT THE SOUTH BUOY AND WINDS DOWN A BIT NORTH BUOY. STILL
SEEING GUSTS TO AROUND GALE FORCE AT SOME OF THE COASTAL OB SITES
ALONG THE EASTERN SHORES...SO PLAN TO HANG ONTO THE GL.W UNTIL MID
MORNING SOUTH. FARTHER NORTH GRADIENT MAY BE A BIT SLOWER TO RELAX
AND WILL HANG ONTO GALES THERE INTO THE EARLY AFTERNOON. WINDS RELAX
FURTHER TONIGHT INTO SUNDAY AS THEY GRADUALLY BACK TO A MORE
SOUTHERLY DIRECTION AS HIGH MOVES EAST INTO THE OHIO VALLEY AND THE
NEXT LOW DEVELOPS OVER THE PLAINS.

SOUTHERLY GRADIENT WILL TIGHTEN UP CONSIDERABLY MONDAY INTO MONDAY
NIGHT AS LOW TRACKS FROM THE CENTRAL PLAINS INTO THE UPPER GREAT
LAKES. MODELS CONTINUE TO SUGGEST THAT WE COULD BE LOOKING AT
SOUTHERLY GALES DURING THIS TIME RANGE OVER SOUTHERN 1/2 TO 2/3 OF
THE LAKE...AND THEN SOUTHWEST GALES OVER NORTHERN LAKE MICHIGAN MON
NIGHT INTO TUES AS THE LOW PULLS OUT AND SLOWLY WEAKENS. BUT MODELS
ARE ALSO SHOWING THE BOUNDARY LAYER REMAINING WELL MIXED OVER THE
LAKE...WHICH MAY NOT BE THE CASE.  COLD AIR ADVECTION AND UPWELLING
FROM THE LARGE WAVES THIS WEEKEND MAY KNOCK DOWN WATER TEMPS LEADING
TO MORE STABLE CONDITIONS OVER THE LAKE THAN MODEL SOUNDINGS
SUGGEST...SO HAVE OPTED TO STICK WITH JUST 30KT WINDS FOR NOW AND
RE-ACCESS THINGS OVER THE WEEKEND BEFORE BUMPING UP WINDS TO GALES.

FOR THE NEARSHORE WILL BE KILLING THE GALE WARNING WITH THIS
MORNING`S ISSUANCE AND REPLACING WITH A SMALL CRAFT ADV THRU THE
AFTERNOON FOR THE ILLINOIS SHORE WHERE WAVES OUT TOWARD THE 5 MILE
OFF SHORE RANGE MAY STILL BE NEAR CRITERIA AND WHERE GUSTS COULD
GET UP TO AROUND CRITERIA AS WELL. FOR THE INDIANA SHORE WHERE THE
FETCH IS LONGER PLAN TO HANG ONTO THE ADV THRU TONIGHT TO GIVE THE
WAVES TIME TO FULLY SUBSIDE.

IZZI

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...GALE WARNING...LMZ080-LMZ366-LMZ565-LMZ567-LMZ669-LMZ671-LMZ673-
     LMZ675-LMZ777-LMZ779-LMZ868-LMZ870-LMZ872-LMZ874-LMZ876-
     LMZ878 UNTIL 9 AM SATURDAY.

     GALE WARNING...LMZ261-LMZ362-LMZ364-LMZ563 UNTIL 3 PM SATURDAY.

     SMALL CRAFT ADVISORY...INDIANA NEARSHORE WATERS UNTIL 4 AM SUNDAY.

     SMALL CRAFT ADVISORY...ILLINOIS NEARSHORE WATERS UNTIL 4 PM SATURDAY.

&&

$$

000
FXUS63 KILX 040830
AFDILX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LINCOLN IL
330 AM CDT SAT SEP 4 2010

.DISCUSSION...
ISSUED 330 AM CDT SAT SEP 4 2010

00Z MODELS ARE IN FAIR AGREEMENT THIS LABOR DAY WEEKEND ALONG
WITH MET AND MAV TEMPERATURE GUIDANCE. NOT TOO MANY CHANGES
PLANNED IN THIS FORECAST PACKAGE AS NICE WEATHER PREVAILS THROUGH
EARLY NEXT WEEK. BELOW NORMAL TEMPERATURES THIS WEEKEND GRADUALLY
MODIFY BACK ABOVE NORMAL MONDAY WITH BREEZY SSW FLOW AS HIGH
PRESSURE RIDGE DRIFTS EAST OF IL SUN/MON.

SHORT TERM...TODAY THROUGH MONDAY NIGHT.

STRONG LOW PRESSURE OF 992 MB OVER EASTERN ONTARIO ALONG WITH
STRONG 500 MB LOW OF 545 DM TO MOVE EAST WHILE 1022 MB HIGH
PRESSURE RIDGE OVER THE GREAT PLAINS DRIFTS EAST OVER IL TONIGHT.
HIGH PRESSURE THEN DRIFTS EAST OF IL SUNDAY AND INTO THE MID
ATLANTIC STATES SUNDAY NIGHT/MON. EXPECT MOSTLY SUNNY SKIES TODAY
WITH SCATTERED CUMULUS CLOUDS AND NW WINDS 10 TO 15 MPH AND GUSTS
UP TO 20-25 MPH THIS AFTERNOON ESPECIALLY FROM I-74 NE. HIGHS IN
THE LOWER 70S TODAY WITH AREAS FROM I-74 NE NEAR 70F. COOLEST DAY
IN CENTRAL IL SINCE MAY 21ST. TONIGHT WILL BE THE COOLEST NIGHT
WITH HIGH PRESSURE RIDGE NEARBY BRINGING CLEAR SKIES AND LIGHT
WINDS WITH LOWS IN THE MID TO UPPER 40S (COOLEST IN EAST CENTRAL IL).
MOSTLY SUNNY SKIES SUNDAY WITH MILDER HIGHS IN THE UPPER 70S TO
NEAR 80F SW AREAS.

MODELS BUILDING UPPER LEVEL RIDGE OVER THE OHIO VALLEY MONDAY
(LABOR DAY) WITH STRONG LOW PRESSURE 998 MB MOVING INTO THE UPPER
MS VALLEY. TIGHTENING PRESSURE GRADIENT OVER IL TO INCREASE SSW
WINDS ALONG WITH WARMER TEMPS IN THE MID 80S CENTRAL IL AND UPPER
80S SE IL. ADDED JUST A SLIGHT CHANCE OF A SHOWER OR THUNDERSTORM
LATER MONDAY NIGHT OVER THE IL RIVER VALLEY WITH A WEAKENING FRONTAL
BOUNDARY MOVING INTO NW IL AS STRONG LOW PRESSURE PASSES WELL
NORTH OF IL INTO NORTHERN WI.

LONG TERM...TUESDAY THROUGH FRIDAY.

WEAKENING FRONT MOVES SE THROUGH CENTRAL/SE IL TUE AND TOWARD THE
OHIO RIVER BY DAWN WED. BEST MOISTURE APPEARS SOUTH OF CENTRAL IL
WHILE BEST UPPER LEVEL DYNAMICS NORTH OVER THE GREAT LAKES. SO
JUST SLIGHT CHANCES OF SHOWERS AND THUNDERSTORMS AND BEST CHANCES
SOUTHERN AREAS. FRONT APPEARS TO MOVE BACK NORTH THU NIGHT AND FRI
AS UPPER LEVEL RIDGE BUILDS BACK INTO THE MS VALLEY RETURNING
WARMER WX.

HUETTL

&&

.AVIATION...
ISSUED 1153 PM CDT FRI SEP 3 2010...FOR THE 06Z TAFS

MINOR VFR CLOUD DECKS AT 5K FT ARE DRIFTING ACROSS PIA/BMI/CMI TAF
SITES...AS THE UPPER LOW CONTINUES TO CHURN OVER THE WESTERN GREAT
LAKES. WE WILL LIKELY SEE THAT CLOUD ACTIVITY LINGER INTO
TOMORROW...BEFORE THE LOW MAKES MORE PROGRESS EASTWARD. THE DRY
LOW LEVEL AIR OF THE SURFACE RIDGE TO THE WEST OF ILLINOIS SHOULD
HELP TO KEEP BROKEN CLOUD DECKS FROM FORMING ON SATURDAY.

WNW WINDS WILL INCREASE WITH THE DAYTIME HEATING TOMORROW...WITH
PEAK WIND GUSTS NEAR 20KT AT TIMES. WINDS SHOULD BE LESS THAN
FRIDAY HOWEVER.

DECREASING WINDS AND CLEAR SKIES SHOULD PREVAIL AFTER 00Z SAT EVE.

SHIMON

&&

.ILX WATCHES/WARNINGS/ADVISORIES...
NONE.

&&

$$

000
FXUS63 KLOT 040830
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
330 AM CDT SAT SEP 4 2010

.DISCUSSION...
330 AM CDT

FORECAST FOCUS CONTINUES TO CENTER ON A FAIRLY ACTIVE PATTERN IN
TERMS OF FRONTAL PROGRESSIONS ANTICIPATED FOR THE UPCOMING
WEEK...ALTHOUGH PRECIPITATION CHANCES WILL BE SOMEWHAT LIMITED WITH
MOISTURE AVAILABILITY QUESTIONS.

WATER VAPOR IMAGERY EARLY THIS MORNING INDICATING UPPER LOW SPINNING
ACROSS FAR SOUTHERN ONTARIO WITH CHANNELED UPPER LEVEL VORT DIGGING
THROUGH BASE OF THIS TROUGH ACROSS THE MID/UPPER MS RIVER VALLEY IN
ASSOCIATION WITH THE UPPER LEVEL JET. SURFACE OBS AND RADAR
IMAGERY HAVE INDICATED BRIEF PERIODS OF SPRINKLES OVER PAST FEW
HOURS LIKELY IN ASSOCIATION WITH WEAK DPVA AND WEAK LOW LEVEL
FRONTOGENESIS. LOW LEVEL COLD ADVECTION ASSOCIATED WITH THIS
BAROCLINIC ZONE WILL USHER IN EVEN COOLER TEMPS THAN
YESTERDAY...ALTHOUGH PLENTY OF INSOLATION AND DEEPER MIXING MAY
PARTIALLY OFFSET THE COOLER LOW LEVEL TEMPERATURES TODAY. TAKING
THE ABOVE INTO CONSIDERATION...HAVE GENERALLY MAINTAINED IDEA OF
TEMPERATURES A FEW DEGREES COOLER TODAY THAN YESTERDAY...IN THE
MID TO UPPER 60S. IN TERMS OF SKY COVER...THE PATCHY STRATOCU
EXTENDING FROM NORTH CENTRAL ILLINOIS INTO THE CHICAGO METRO AREA
SHOULD CONTINUE TO SHIFT EAST/SOUTHEAST THIS MORNING...AND WILL
BE REPLACED BY SOME DIURNAL FLAT CU DEVELOPMENT. SOME LIGHT LAKE
EFFECT RAIN SHOWERS WILL LIKELY REMAIN JUST TO THE EAST/NORTHEAST
OF PORTER COUNTY INDIANA...ESPECIALLY CONSIDERING LOW LEVEL WINDS
SHOULD BEGIN TO BACK THIS MORNING AS A LOW LEVEL RIDGE SINKS
SOUTHEASTWARD INTO THE MID MS RIVER VALLEY.

TEMPERATURE ADVECTION TO BECOME MORE NEUTRAL TONIGHT...ALTHOUGH A
BETTER CHANCE FOR COOLISH LOWS IN THE MID 40S IN STORE FOR TONIGHT
GIVEN GREATER DECOUPLING POTENTIAL GIVEN PROXIMITY OF SFC RIDGE
AXIS. WOULD SUSPECT THAT SOME OF THE FAVORED LOW LYING COOL SPOTS
MAY EVEN FLIRT WITH 40 DEGREES FOR MINS TONIGHT.

ON SUNDAY...SFC LOW IS EXPECTED TO DEEPEN ACROSS THE CENTRAL HIGH
PLAINS AS NEXT SIGNIFICANT UPPER LEVEL TROUGH MOVES ACROSS NWRN
CONUS. THE LOW LEVEL RIDGE SETTLING INTO LOWER/MID MS RIVER VALLEY
OVER NEXT 24 HOURS WILL LIMIT MOISTURE RETURN INITIALLY IN ADVANCE
OF THIS TROUGH. GIVEN INCREASING UNCERTAINTY OF LOW LEVEL
MOISTURE AVAILABILITY...DID GO AHEAD AND PULL THE SLIGHT CHANCE
POPS FOR RAIN SHOWERS SUNDAY AFTERNOON. BY SUNDAY
EVENING...ISENTROPIC LIFT SHOULD BEGIN TO STRENGTHEN MORE
SUBSTANTIALLY WITH SOME BETTER MID LEVEL LAPSE RATES DEVELOPING.
AT THIS POINT...WOULD SUSPECT THAT THE BEST CHANCE OF ELEVATED
SHOWERS/STORMS WOULD BE JUST NORTH OF FORECAST AREA ACROSS WI AND
INTO THE UPPER GREAT LAKES AS ZONE OF STRONGER ISENTROPIC ASCENT
LIFTS NORTHWARD WITH THE WARM FRONTAL-LIKE FEATURE. THIS ALSO
APPEARS TO BE A MORE SYNOPTICALLY FAVORED REGION FOR LARGE SCALE
ASCENT WITH WEAK UPPER JET STREAK COUPLING NOTED IN NAM/GFS SOLUTIONS.

LOW/MID LEVELS SHOULD DRY OUT BY EARLY MONDAY AS LOW LEVEL WARM
FRONTS LIFTS THROUGH NORTHERN GREAT LAKES AND THUS DRY CONDITIONS
EXPECTED TO CONTINUE THROUGH THE DAY MONDAY. UPPER DYNAMICS
ASSOCIATED WITH THE AFOREMENTIONED UPPER TROUGH WILL BEGIN TO
INCREASE BY MONDAY NIGHT...BUT ESPECIALLY AGAIN TO THE NORTH OF
THE AREA. THUS...WILL HANDLE MONDAY NIGHT PERIOD WITH JUST SLIGHT
CHANCE POPS FOR TSRA. TEMPERATURES ON MONDAY IN THE WARM SECTOR
SHOULD SHOOT BACK UP INTO THE LOWER TO MID 80S ACROSS MUCH OF THE
AREA...AND WITH THIS WARMING AND INITIALLY DRY LOW LEVELS COMES
SOME CONCERN FOR FIRE WEATHER...WHICH IS HIGHLIGHTED BELOW.

SYSTEM WILL OCCLUDE ACROSS UPPER MIDWEST TUESDAY WITH COLD FRONT
EXPECTED TO STALL OUT ACROSS OR JUST THE SOUTH OF THE AREA...AND
THEN BEGIN TO RETURN NORTHWARD AS A WARM FRONT AGAIN TOWARD THE END
OF THE WEEK. THIS RETURN WARM/MOIST ADVECTION COULD BE CONDUCIVE FOR
SOME SCT SHOWERS/STORMS BY THURS. HOWEVER...MEDIUM RANGE MODELS
DIVERGE TO A LARGER DEGREE WITH NEXT SHORT WAVE TROUGH FOR
THURS/FRI WITH ECMWF A SIGNIFICANTLY SLOWER SOLUTION COMPARED TO
GFS/NCEP ENSEMBLES. CONFIDENCE IN TIMING PRECIP CHANCES IS LOW AT
THIS TIME...SO DID NOT CHANGE LOW CHANCE POPS THURS/FRI...WITH SOME
HIGHER CONFIDENCE IN AT LEAST A SHIFT BACK TO WARMER TEMPS AGAIN
TOWARD THE END OF THE PERIOD.

MARSILI

&&

.FIRE WEATHER...
330 AM CDT

ON MONDAY...SOUTH WINDS ARE EXPECTED TO INCREASE INTO THE 15 TO 25
MPH RANGE WITH SOME GUSTS TO 30 MPH OR SLIGHTLY HIGHER. THERE IS A
POSSIBILITY THAT SOME DRIER LOW LEVEL AIR MAY MIX DOWN TO THE
SURFACE WHICH WOULD RESULT IN MINIMUM AFTERNOON RELATIVE
HUMIDITIES AROUND OR LESS THAN 30 PERCENT. CONFIDENCE IN MEETING
RED FLAG CONDITIONS IS LOW AT THIS POINT GIVEN UNCERTAINTY AS TO
HOW MUCH OF THIS LOW LEVEL DRY AIR WILL MIX TO THE SURFACE...AND
ALSO 10 HR FUEL MOISTURES ARE STILL RUNNING ON THE HIGH SIDE
ACROSS THE AREA.

MARSILI

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 06Z...

GUSTY NW WINDS AND SCT-BKN VFR CIGS LIKELY TO PERSIST INTO SAT
AFTERNOON...THOUGH WEATHER NOT EXPECTED TO HAVE ADVERSE IMPACT ON
OPS.

IZZI

//DISCUSSION...UPDATED 06Z...

LOW LEVELS SHOULD REMAIN MIXED ENOUGH OVERNIGHT TO SEE AT LEAST
OCNL GUSTS UP TO AROUND 20KT...PARTICULARLY AS THE BKN MOSTLY VFR
STRATOCUMULUS DECK PIVOTS SE INTO NRN IL. THERE ARE A FEW VERY
ISOLD -SHRA WITH THE STRATOCUMULUS BUT APPEARS TO BE TOO ISOLD AND
INSIGNIFICANT TO INCLUDE IN THE TAFS. SOME MIXED SUNSHINE AND
HEATING SATURDAY SHOULD SUSTAIN GUSTS TO AROUND 20KT..EVEN THOUGH
PRESSURE GRADIENT WILL BE GRADUALLY RELAXING. SCT-BKN STRATOCU
DECK LIKELY TO PERSIST INTO THE AFTERNOON SATURDAY WITH DAYTIME
HEATING LIKELY TO HELP THIS PROCESS ALONG. EXPECT SCT-BKN STRATOCU
TO FADE WITH SUNSET SAT EVENING AND WINDS SHOULD ALSO RELAX WITH
RIDGE AXIS MOVING INTO THE REGION.

IZZI

//ORD AND MDW CONFIDENCE...UPDATED 06Z...

HIGH CONFIDENCE IN ALL ASPECTS OF THE FORECAST.

IZZI

//OUTLOOK FOR ORD/MDW FOR 12Z SUNDAY-12Z FRIDAY...UPDATED 06Z...

SUNDAY...SLIGHT CHC -SHRA SUN NIGHT...OTHERWISE VFR.
MONDAY...VFR. STRONG/GUSTY SOUTH WINDS LATE MORNING INTO AFTERNOON.
TUESDAY AND WEDNESDAY...VFR.
THURSDAY...SLIGHT CHC TSRA...OTHERWISE VFR.

IZZI

&&

.MARINE...
215 AM CDT

SEEING SIGNS OF THE PRESSURE GRADIENT AND WINDS STARTING TO SLOWLY
EASE OVER THE LAKE...WITH NO GALE FORCE GUSTS FOR THE PAST COUPLE
HOURS AT THE SOUTH BUOY AND WINDS DOWN A BIT NORTH BUOY. STILL
SEEING GUSTS TO AROUND GALE FORCE AT SOME OF THE COASTAL OB SITES
ALONG THE EASTERN SHORES...SO PLAN TO HANG ONTO THE GL.W UNTIL MID
MORNING SOUTH. FARTHER NORTH GRADIENT MAY BE A BIT SLOWER TO RELAX
AND WILL HANG ONTO GALES THERE INTO THE EARLY AFTERNOON. WINDS RELAX
FURTHER TONIGHT INTO SUNDAY AS THEY GRADUALLY BACK TO A MORE
SOUTHERLY DIRECTION AS HIGH MOVES EAST INTO THE OHIO VALLEY AND THE
NEXT LOW DEVELOPS OVER THE PLAINS.

SOUTHERLY GRADIENT WILL TIGHTEN UP CONSIDERABLY MONDAY INTO MONDAY
NIGHT AS LOW TRACKS FROM THE CENTRAL PLAINS INTO THE UPPER GREAT
LAKES. MODELS CONTINUE TO SUGGEST THAT WE COULD BE LOOKING AT
SOUTHERLY GALES DURING THIS TIME RANGE OVER SOUTHERN 1/2 TO 2/3 OF
THE LAKE...AND THEN SOUTHWEST GALES OVER NORTHERN LAKE MICHIGAN MON
NIGHT INTO TUES AS THE LOW PULLS OUT AND SLOWLY WEAKENS. BUT MODELS
ARE ALSO SHOWING THE BOUNDARY LAYER REMAINING WELL MIXED OVER THE
LAKE...WHICH MAY NOT BE THE CASE.  COLD AIR ADVECTION AND UPWELLING
FROM THE LARGE WAVES THIS WEEKEND MAY KNOCK DOWN WATER TEMPS LEADING
TO MORE STABLE CONDITIONS OVER THE LAKE THAN MODEL SOUNDINGS
SUGGEST...SO HAVE OPTED TO STICK WITH JUST 30KT WINDS FOR NOW AND
RE-ACCESS THINGS OVER THE WEEKEND BEFORE BUMPING UP WINDS TO GALES.

FOR THE NEARSHORE WILL BE KILLING THE GALE WARNING WITH THIS
MORNING`S ISSUANCE AND REPLACING WITH A SMALL CRAFT ADV THRU THE
AFTERNOON FOR THE ILLINOIS SHORE WHERE WAVES OUT TOWARD THE 5 MILE
OFF SHORE RANGE MAY STILL BE NEAR CRITERIA AND WHERE GUSTS COULD
GET UP TO AROUND CRITERIA AS WELL. FOR THE INDIANA SHORE WHERE THE
FETCH IS LONGER PLAN TO HANG ONTO THE ADV THRU TONIGHT TO GIVE THE
WAVES TIME TO FULLY SUBSIDE.

IZZI

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...GALE WARNING...LMZ080-LMZ366-LMZ565-LMZ567-LMZ669-LMZ671-LMZ673-
     LMZ675-LMZ777-LMZ779-LMZ868-LMZ870-LMZ872-LMZ874-LMZ876-
     LMZ878 UNTIL 9 AM SATURDAY.

     GALE WARNING...LMZ261-LMZ362-LMZ364-LMZ563 UNTIL 3 PM SATURDAY.

     SMALL CRAFT ADVISORY...INDIANA NEARSHORE WATERS UNTIL 4 AM SUNDAY.

     SMALL CRAFT ADVISORY...ILLINOIS NEARSHORE WATERS UNTIL 4 PM SATURDAY.

&&

$$

000
FXUS63 KLOT 040715
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
215 AM CDT SAT SEP 4 2010

.DISCUSSION...
839 PM CDT

IR IMAGERY THIS EVENING CONTINUES TO SHOW POTENT UPPER LEVEL LOW
PRESSURE OVER LAKE SUPERIOR...AND HI-RES GUIDANCE SUGGESTS A
GRADUAL EAST TRACK THROUGH THE NEXT 24HRS. UNIFORM DEW PTS ACROSS
THE REGION IN THE MID/UPR 40S FROM INITIAL SUBSIDENCE THIS AFTN
AND STRONG MIXING...HOWEVER THE SFC MAY NOT COMPLETELY REALIZE THE
COOL AIR ALOFT OVERNIGHT. A NARROW CHANNEL OF MOISTURE EXISTS BTWN
925-850MB THAT MAY KEEP SOME CLOUDS OVER NORTHERN IL/NORTHWEST IN.
UNDER THIS SHALLOW CHANNEL OF MOISTURE ISO SHRA HAVE PERSISTED
WITH A FEW LOCATIONS IN CENTRAL WISC REPORTING MODERATE RAINFALL
FOR A FEW MOMENTS. CURRENTLY DO NOT ANTICIPATE THIS TO VENTURE
SOUTH INTO OUR CWFA...HOWEVER FEEL ISO SHRA ARE POSSIBLE.

ISALLOBARIC PRES CHG HAS SLACKENED TO ARND 1 TO 2 MB...AS HEIGHTS
ARE BEGINNING TO RISE. THE PRESSURE GRADIENT APPEARS TO PERSIST
HOWEVER...WHICH COULD PREVENT FULL DECOUPLING OF THE BNDRY LYR
AND ALLOW ENOUGH FRICTION TO KEEP SFC TEMPS FROM FALLING INTO THE
MID 40S. FEEL A FEW LOCATIONS MAY INDEED FULLY
DECOUPLE...ESPECIALLY FAR WESTERN SECTIONS OF THE CWFA ELSEWHERE
HAVE BUMPED TEMPS UP A FEW DEG INTO THE UPR 40S. DOWNTOWN CHICAGO
MAY ONLY SEE OVERNIGHT TEMPS FALL INTO THE MID 50S BY DAYBREAK.

BEACHLER

//PREV DISCUSSION...
254 PM CDT

A DEEP LOW PRESSURE SYSTEM OVER THE NORTHERN GREAT LAKES THIS
MORNING IS BRINGING DOWN COLD CANADIAN AIR AND BLUSTERY WINDS. H85
TEMPS IN THE AROUND 7-8C ADVECTING OVER NORTHERN ILLINOIS THIS
AFTERNOON ARE HELPING TO CREATE STEEP LOW LEVEL LAPSE RATES ALLOWING
FOR STRONGER WINDS ALOFT TO MIX DOWN. AREA OBSERVATIONS CURRENTLY
SHOWING FREQUENT GUSTS INTO THE 30-35 MPH RANGE WITH THE POTENTIAL
FOR HIGHER GUSTS THIS EVENING AS A TROF PINWHEELS AROUND THE MAIN
LOW BRINGING DOWN EVEN COLDER AIR. H85 TEMPERATURES WILL PROBABLY
BOTTOM OUT IN THE LOW SINGLE DIGITS THIS EVENING. COLD AIR STRATOCU
EVIDENT ON SATELLITE IMAGERY MOVING AROUND THE BACKSIDE OF THE LOW.
WHILE RADAR IS CURRENTLY QUIET OVER THE FORECAST AREA...CANT RULE
OUT A COUPLE SHOWERS DEVELOPING AS THE TROF MOVES THROUGH THE AREA
THIS EVENING.

SATURDAY WILL SEE SIMILAR CONDITIONS...COOL AND BREEZY...THOUGH WITH
HIGH PRESSURE GRADUALLY BUILDING INTO THE WEST...SHOULD SEE A SLOW
DECREASE IN THE WINDS THROUGH THE DAY AS THE PRESSURE GRADIENT
SLACKENS. THE SURFACE RIDGE SLIDES TO THE EAST ON SUNDAY AND WARMER
SOUTHERLY FLOW OPENS BACK UP. WILL SEE A GRADUAL WARMING TREND
SUNDAY THROUGH THE EARLY PART OF THE WEEK WITH SUMMERLIKE CONDITIONS
RETURNING MONDAY.

MODELS ARE IN GENERAL AGREEMENT THAT THE PATTERN WILL BECOME MORE
ZONAL AND PROGRESSIVE FOR THE EARLY PART OF NEXT WEEK...WITH SOME
TIMING ISSUES STARTING TO CREEP IN. A LOW PRESSURE SYSTEM IS PROGGED
TO DEEPEN OVER THE CENTRAL PLAINS WITH A WARM FRONT LIFTING THROUGH
THE AREA SOMETIME EARLY MONDAY MORNING BRINGING A CHANCE OF
SHOWERS. A TRAILING COLD FRONT THEN LAYS OUT ACROSS THE
FORECAST AREA MONDAY NIGHT INTO TUESDAY...LOSING ITS PUSH AS IT
BECOMES MORE ALIGNED WITH UPPER WINDS WHILE MORE FAVORABLE UPPER
SUPPORT OUTRUNS THE SFC FRONT AS THE H5 TROF LIFTS INTO CANADA.

BMD

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 06Z...

GUSTY NW WINDS AND SCT-BKN VFR CIGS LIKELY TO PERSIST INTO SAT
AFTERNOON...THOUGH WEATHER NOT EXPECTED TO HAVE ADVERSE IMPACT ON
OPS.

IZZI

//DISCUSSION...UPDATED 06Z...

LOW LEVELS SHOULD REMAIN MIXED ENOUGH OVERNIGHT TO SEE AT LEAST
OCNL GUSTS UP TO AROUND 20KT...PARTICULARLY AS THE BKN MOSTLY VFR
STRATOCUMULUS DECK PIVOTS SE INTO NRN IL. THERE ARE A FEW VERY
ISOLD -SHRA WITH THE STRATOCUMULUS BUT APPEARS TO BE TOO ISOLD AND
INSIGNIFICANT TO INCLUDE IN THE TAFS. SOME MIXED SUNSHINE AND
HEATING SATURDAY SHOULD SUSTAIN GUSTS TO AROUND 20KT..EVEN THOUGH
PRESSURE GRADIENT WILL BE GRADUALLY RELAXING. SCT-BKN STRATOCU
DECK LIKELY TO PERSIST INTO THE AFTERNOON SATURDAY WITH DAYTIME
HEATING LIKELY TO HELP THIS PROCESS ALONG. EXPECT SCT-BKN STRATOCU
TO FADE WITH SUNSET SAT EVENING AND WINDS SHOULD ALSO RELAX WITH
RIDGE AXIS MOVING INTO THE REGION.

IZZI

//ORD AND MDW CONFIDENCE...UPDATED 06Z...

HIGH CONFIDENCE IN ALL ASPECTS OF THE FORECAST.

IZZI

//OUTLOOK FOR ORD/MDW FOR 12Z SUNDAY-12Z FRIDAY...UPDATED 06Z...

SUNDAY...SLIGHT CHC -SHRA SUN NIGHT...OTHERWISE VFR.
MONDAY...VFR. STRONG/GUSTY SOUTH WINDS LATE MORNING INTO AFTERNOON.
TUESDAY AND WEDNESDAY...VFR.
THURSDAY...SLIGHT CHC TSRA...OTHERWISE VFR.

IZZI

&&

.MARINE...
215 AM CDT

SEEING SIGNS OF THE PRESSURE GRADIENT AND WINDS STARTING TO SLOWLY
EASE OVER THE LAKE...WITH NO GALE FORCE GUSTS FOR THE PAST COUPLE
HOURS AT THE SOUTH BUOY AND WINDS DOWN A BIT NORTH BUOY. STILL
SEEING GUSTS TO AROUND GALE FORCE AT SOME OF THE COASTAL OB SITES
ALONG THE EASTERN SHORES...SO PLAN TO HANG ONTO THE GL.W UNTIL MID
MORNING SOUTH. FARTHER NORTH GRADIENT MAY BE A BIT SLOWER TO RELAX
AND WILL HANG ONTO GALES THERE INTO THE EARLY AFTERNOON. WINDS RELAX
FURTHER TONIGHT INTO SUNDAY AS THEY GRADUALLY BACK TO A MORE
SOUTHERLY DIRECTION AS HIGH MOVES EAST INTO THE OHIO VALLEY AND THE
NEXT LOW DEVELOPS OVER THE PLAINS.

SOUTHERLY GRADIENT WILL TIGHTEN UP CONSIDERABLY MONDAY INTO MONDAY
NIGHT AS LOW TRACKS FROM THE CENTRAL PLAINS INTO THE UPPER GREAT
LAKES. MODELS CONTINUE TO SUGGEST THAT WE COULD BE LOOKING AT
SOUTHERLY GALES DURING THIS TIME RANGE OVER SOUTHERN 1/2 TO 2/3 OF
THE LAKE...AND THEN SOUTHWEST GALES OVER NORTHERN LAKE MICHIGAN MON
NIGHT INTO TUES AS THE LOW PULLS OUT AND SLOWLY WEAKENS. BUT MODELS
ARE ALSO SHOWING THE BOUNDARY LAYER REMAINING WELL MIXED OVER THE
LAKE...WHICH MAY NOT BE THE CASE.  COLD AIR ADVECTION AND UPWELLING
FROM THE LARGE WAVES THIS WEEKEND MAY KNOCK DOWN WATER TEMPS LEADING
TO MORE STABLE CONDITIONS OVER THE LAKE THAN MODEL SOUNDINGS
SUGGEST...SO HAVE OPTED TO STICK WITH JUST 30KT WINDS FOR NOW AND
RE-ACCESS THINGS OVER THE WEEKEND BEFORE BUMPING UP WINDS TO GALES.

FOR THE NEARSHORE WILL BE KILLING THE GALE WARNING WITH THIS
MORNING`S ISSUANCE AND REPLACING WITH A SMALL CRAFT ADV THRU THE
AFTERNOON FOR THE ILLINOIS SHORE WHERE WAVES OUT TOWARD THE 5 MILE
OFF SHORE RANGE MAY STILL BE NEAR CRITERIA AND WHERE GUSTS COULD
GET UP TO AROUND CRITERIA AS WELL. FOR THE INDIANA SHORE WHERE THE
FETCH IS LONGER PLAN TO HANG ONTO THE ADV THRU TONIGHT TO GIVE THE
WAVES TIME TO FULLY SUBSIDE.

IZZI

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...GALE WARNING...LMZ080-LMZ366-LMZ565-LMZ567-LMZ669-LMZ671-LMZ673-
     LMZ675-LMZ777-LMZ779-LMZ868-LMZ870-LMZ872-LMZ874-LMZ876-
     LMZ878 UNTIL 9 AM SATURDAY.

     GALE WARNING...LMZ261-LMZ362-LMZ364-LMZ563 UNTIL 3 PM SATURDAY.

     SMALL CRAFT ADVISORY...INDIANA NEARSHORE WATERS UNTIL 4 AM SUNDAY.

     SMALL CRAFT ADVISORY...ILLINOIS NEARSHORE WATERS UNTIL 4 PM SATURDAY.

&&

$$

      
      

  
    
    
  
  
    
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