Area Forecast Discussion
Issued by NWS Chicago, IL

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000
FXUS63 KLOT 042209
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
509 PM CDT TUE AUG 4 2015

.SHORT TERM...
221 PM CDT

THROUGH WEDNESDAY

A WEAK SURFACE TROUGH REMAINS IN PLACE ACROSS SOUTHERN LAKE MICHIGAN
THIS AFTERNOON...WITH HIGH PRESSURE TO OUR WEST...AND A STATIONARY
FRONT STRETCHED FROM THE SOUTHERN PLAINS AND EASTWARD ACROSS THE
OHIO/TENNESSEE VALLEYS. ALOFT...NW FLOW PERSISTS ON THE BACK SIDE OF
THE UPPER LOW JUST SOUTH OF HUDSON BAY...RIDGING ACROSS THE CENTRAL
PLAINS INTO THE UPPER MIDWEST...WITH A DISTURBANCE UNDER CUTTING THE
RIDGE CLOSER TO THE SURFACE FRONT.

THUNDERSTORMS ARE ONGOING THOUGH WEAKENING CLOSER TO THE
WAVE/SURFACE FRONT...BUT WITH HIGH PRESSURE JUST TO OUR WEST...WE
ARE JUST SEEING SOME HIGH CLOUDS FROM THIS ACTIVITY...ALONG WITH
SOME DAYTIME HEATING INDUCED CUMULUS ASSOCIATED WITH THE UPPER
LOW. THE UPPER LOW WILL PULL EAST TONIGHT INTO
WEDNESDAY...ALLOWING THE UPPER RIDGE TO SLIDE OVERHEAD TOMORROW.
PRECIPITATION ASSOCIATED WITH THE DISTURBANCE UNDERCUTTING THE
RIDGE WILL REMAIN TO OUR SOUTH AS SURFACE HIGH PRESSURE MOVES
ALONG AND EAST OF LAKE MICHIGAN AND ANCHORING THE SURFACE FRONT
ACROSS CENTRAL AND SOUTHERN ILLINOIS. THIS WILL MEAN DRY
CONDITIONS FOR THE FORECAST AREA TOMORROW DURING THE DAYTIME
HOURS. WITH THE HIGH EAST OF THE LAKE...ONSHORE FLOW WILL KEEP
LAKE ADJACENT AREAS COOLER IN THE 70S...WHILE AREAS INLAND STAY
CLOSE TO WHERE THEY ARE PEAKING TODAY IN THE LOW 80S.

KMD

&&

.LONG TERM...
308 PM CDT

WEDNESDAY NIGHT THROUGH TUESDAY...

MORNING GUIDANCE FINALLY COMING INTO BETTER AGREEMENT WITH
EVOLUTION OF UPSTREAM ENERGY...AND ASSOCIATED SURFACE REFLECTION
AND PRECIP. HAVE REMOVED OR LOWERED POPS FROM WEDNESDAY NIGHT INTO
THURSDAY NIGHT AS GUIDANCE CONSISTENT WITH KEEPING PRECIP AXIS TO
THE SOUTH OF THE CWA...INTO CENTRAL AND SOUTHERN ILLINOIS/INDIANA.
SOME GUIDANCE TRYING TO INCH THIS PRECIP FURTHER NORTH ON
THURSDAY...BUT I WOULD THINK A CONTINUED SOUTHERLY TREND WITH THIS
SYSTEM AND PRECIP WOULD LIKELY OCCUR. HAVE LEFT A SLIGHT CHANCE OF
SHOWERS ACROSS A PORTION OF EAST CENTRAL ILLINOIS AND NORTHWEST
INDIANA FOR THAT TIME...BUT COULD SEE THIS BEING REMOVED WITH
LATER FORECASTS. DESPITE PRECIP STAYING TO THE SOUTH...NORTHERN
ILLINOIS AND NORTHWEST INDIANA WILL SEE MID/HIGH LEVEL CLOUD COVER
CONTINUE TO SPREAD NORTH. EXTENT OF CLOUD COVER IS LITTLE
UNCERTAIN AT THIS TIME WEDNESDAY NIGHT BUT SHOULD SEE THE BULK OF
THESE CLOUDS SLIDE SOUTHEAST ON THURSDAY WITH SKIES BECOMING MORE
PARTLY CLOUDY...AND WITH TEMPS EXPECTED TO BE NEAR NORMAL AROUND
80 DEGREES.

MODEL GUIDANCE IN FAIR AGREEMENT WITH THE GENERAL WEATHER PATTERN
TOWARDS THE END OF THE WORK WEEK AND INTO THE START OF THE
WEEKEND...ALTHOUGH SOME SLIGHT UNCERTAINTY IS IN PLACE WITH EXACT
TIMING AND COVERAGE OF EXPECTED WEATHER. ENERGETIC WESTERLY FLOW
WILL TRY TO USHER IN BETTER FORCING AND CHANCES FOR SHOWERS AND
THUNDERSTORMS BY FRIDAY AND FRIDAY NIGHT...BUT ONCE AGAIN
CONFIDENCE ON TIMING AND COVERAGE/PLACEMENT OF ASSOCIATED PRECIP
IS LOW. AT THIS TIME...BEST CHANCES FOR PRECIP WILL BE FRIDAY
AFTERNOON AS SURFACE TROUGH AND BOUNDARY PUSH THROUGH WITH AREAS
ACROSS NORTHERN ILLINOIS THE LOCATION WITH HIGHEST POPS. WITH THE
BEST FORCING REMAINING TO THE NORTH OF THE AREA ITS POSSIBLE THAT
THIS PRECIP WILL STAY FURTHER NORTH. STILL MAINTAINED CHANCE POPS
THOUGH...AS FORCING ACROSS NORTHERN WILL BE SUFFICIENT FOR AT
LEAST SOME TYPE OF SCATTERED DEVELOPMENT. INSTABILITY WILL
INCREASE ON FRIDAY AND DO THINK THUNDER WILL BE POSSIBLE BUT WITH
THE INSTABILITY AXIS STILL WEST OF THE AREA DURING THIS TIME...AM
NOT OVERLY CONCERNED AT THIS TIME FOR SEVERE WEATHER. HOWEVER...IF
INSTABILITY WERE TO INCREASE QUICKER...THAN SOME ISOLATED STRONGER
DEVELOPMENT COULD BE POSSIBLE.

RODRIGUEZ

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 22Z...

* POSSIBLE LAKE BREEZE EARLY EVENING.
* EASTERLY WINDS NEAR 10KT WEDNESDAY. CMS

//DISCUSSION...UPDATED 22Z...

WESTERLY WINDS HAVE BEGUN TO DIMINISH THIS AFTERNOON AND THE
LAKE BREEZE HAS MOVED INLAND ACROSS EASTERN COOK COUNTY. FAIRLY
LOW CONFIDENCE REGARDING HOW FAR INLAND THIS WILL MOVE AND IF IT
WILL REACH MDW...OR ORD. MAINTAINED WESTERLY WINDS AT ORD/MDW FOR
NOW BUT WILL NEED TO MONITOR TRENDS. CMS

PREVIOUS 18Z DISCUSSION...

HIGH PRESSURE WILL CONTINUE ACROSS NORTHERN IL/NORTHWEST
IN WHILE LOW PRESSURE SITS OVER NRN QUEBEC. THIS WILL KEEP WLY-
WNWLY WINDS OVER THE REGION. DEEP LAYER MIXING WILL ALLOW GUSTS
UP TO ARND 20KT THROUGH SUNSET. THESE WINDS SHOULD BE STRONG
ENOUGH WINDS TO PREVENT A LAKE BREEZE FROM PUSHING INLAND. WINDS
WILL DIMINISH ARND SUNSET...AND BECM LGT/VRBL DURG THE EARLY
MORNING HOURS. DRY AIR WILL CONTINUE TO LIMIT THE CLOUD COVER
TODAY...WITH JUST SOME STRATOCU GENERATED BY CYCLONIC CURVATURE TO
THE UPPER LEVEL PATTERN AND SOME CIRRUS BLOW-OFF FROM
THUNDERSTORMS OVER THE UPPER MISSOURI VALLEY.

AS HIGH PRESSURE SHIFTS EAST OVERNIGHT...WINDS WILL TURN NORTHEAST
SHORTLY AFTER DAYBREAK WEDNESDAY AND THEN MORE ELY DURG THE
AFTERNOON. WIND SPEEDS SHOULD SLOWLY INCREASING TO 8-10 KT BY
TOMORROW AFTERNOON.

KREIN

//ORD AND MDW CONFIDENCE...UPDATED 22Z...

* LOW FOR LAKE BREEZE THRU EARLY EVENING.
* MEDIUM FOR WINDS WEDNESDAY. CMS

//OUTLOOK FOR ORD/MDW FOR 00Z THURSDAY-12Z TUESDAY...UPDATED 12Z...

WEDNESDAY NIGHT THROUGH THURSDAY...VFR.

FRIDAY...MAINLY VFR. CHANCE OF SHOWERS AND THUNDERSTORMS.

SATURDAY THROUGH MONDAY...MAINLY VFR. SLIGHT CHANCE OF
SHOWERS/THUNDERSTORMS.

BEACHLER

&&

.MARINE...
448 PM CDT

WEAK NORTHERLY FLOW IS IN PLACE ACROSS THE LAKE THIS AFTERNOON
WHILE WEAK HIGH PRESSURE IS SITUATED JUST SOUTH OF THE LAKE.
STRONGER HIGH PRESSURE TO THE WEST AND NORTHWEST OF THE LAKE WILL
DROP SOUTHEAST ACROSS THE LAKES THROUGH MID WEEK...AND THEN
CONTINUE TO THE EAST TOWARDS THE END OF THE WORK WEEK. SPEEDS
DURING THIS TIME WILL REMAIN RELATIVELY LIGHT...BEFORE TURNING
MORE SOUTHERLY AND INCREASING BY THE END OF THE WORK WEEK.

RODRIGUEZ

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...NONE.
&&

$$

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