Area Forecast Discussion
Issued by NWS Chicago, IL

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000
FXUS63 KLOT 011936
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
236 PM CDT TUE SEP 1 2015

.SHORT TERM...
225 PM CDT

THROUGH WEDNESDAY...

AN UPPER LEVEL LOW IS OVER CENTRAL INDIANA AND IT WILL SLIDE
SOUTHEAST THROUGH WEDNESDAY MORNING.  THUNDERSTORMS FORMED ALONG THE
WESTERN EDGE OF THIS LOW EARLIER THIS MORNING AND AFTERNOON...AND
HAVE NOW SUBSIDED. A FEW ISOLATED THUNDERSTORMS ARE POSSIBLE SOUTH
AND EAST OF I-55 THROUGH THIS AFTERNOON BUT THE AFTERNOON SHOULD BE
DRY FOR MOST AREAS.  THE LARGE UPPER LEVEL RIDGE REMAINS IN PLACE
OVER THE CONUS TONIGHT ALLOWING SOUTHWEST WINDS TO WEAKEN. DID NOT
MAKE ANY CHANGES TO LOW TEMPS TONIGHT WITH LOWS IN THE UPPER 60S TO
LOWER 70S.

AN UPPER LEVEL WAVE MOVES OVER WISCONSIN WEDNESDAY WITH A TRAILING
VORTICITY STREAMER THROUGH IOWA. EXPECTING CONVECTION TO BLOSSOM TO
OVER WISCONSIN AND IOWA AND REMAIN OUT OF IL AND INDIANA DURING THE
DAYTIME HOURS TOMORROW.  WINDS WILL BECOME WEST AND THERE IS CHANCE
OF A LAKE BREEZE TOMORROW. WINDS WILL BE AT 20KT OR LESS IN THE
LOWEST 1000 FT OF THE ATMOSPHERE IN THE MORNING AND THEN WEAKEN AS
THE DAY GOES ON. AS SUCH...IF A LAKE BREEZE DOES FORM...IT WOULD BE
LATE IN THE AFTERNOON OR EARLY EVENING AS THE WINDS RELAX.
THEREFORE...RAISED HIGH TEMPS DOWNTOWN INTO THE LOW 90S...WITH HIGH
TEMPS ACROSS THE REGION IN THE LOW 90S.  DEWPOINTS WILL ONCE AGAIN
BE IN THE 70S LEADING TO HEAT INDICES IN THE MID TO UPPER 90S.

ALSO ISSUED AN AIR QUALITY STATEMENT FOR LAKE AND PORTER COUNTIES IN
INDIANA AS AN AIR QUALITY DAY WAS FORECAST FOR PARTS OF NW INDIANA
BY THE INDIANA DEPARTMENT OF ENVIRONMENTAL MANAGEMENT. OZONE WILL BE
THE PRIMARY POLLUTANT WEDNESDAY.

JEE

&&

.LONG TERM...
225 PM CDT

WEDNESDAY NIGHT THROUGH TUESDAY...

A WEAK MID-LVL WAVE WILL BE SLIDING EAST ACROSS THE UPPER MIDWEST
WEDNESDAY EVENING...AND MAY BRING AN ISOLATED SHOWER/THUNDERSTORM TO
SOUTHERN WISC AND COULD PUSH INTO NORTHERN IL EARLY THUR. GUIDANCE
THEN PROGRESSIVELY BUILDS THE MID-LVL HEIGHTS OVER THE PLAINS AND
EVENTUALLY ARRIVES OVER THE FORECAST AREA THUR EVE. THIS SHOULD THEN
LIMIT THE POTENTIAL FOR CONVECTION/PRECIP LATE IN THE WEEK. THE BULK
OF CONVECTION WILL BE DISPLACED WELL NORTH INTO CANADA AND PERHAPS
NORTHERN WISC.

WARM THERMAL RIDGE REMAINS IN PLACE THROUGH THE END OF THE WEEK INTO
THE WEEKEND...SUPPORTING HIGHS IN THE UPR 80S TO ARND 90. WITH
GENERALLY SOUTHERLY FLOW AT THE SFC...LOW LEVEL MOISTURE WILL
CONTINUE TO ADVECT NORTH AND LINGER OVER THE REGION. THIS WILL KEEP
DEW POINTS ELEVATED IN THE UPR 60S TO ARND 70 LATE IN THE WEEK THRU
THE WEEKEND.

ENSEMBLES CONTINUE TO POINT TOWARDS A MORE ROBUST MID-LVL SHORTWAVE
ARRIVING ACROSS THE PAC-NW SAT/SUN AND STEADILY SLIDING EAST.
GUIDANCE HAS BEEN LEANING TOWARDS A WAVE DEVELOPING ALONG THE LEE-
SIDE OF THIS SHORTWAVE EARLY NEXT WEEK...WITH AN INCREASED CHANCE
FOR SHOWERS/THUNDERSTORMS FOR THE FIRST HALF OF NEXT WEEK. THIS MAY
BRING ABOUT A PATTERN SHIFT...AS ENSEMBLES INDICATE THE ROBUST
THERMAL RIDGE WILL BE PUSHING EAST AND THE ARRIVAL OF COOLER AIR
BEYOND THE CURRENT EXTENDED PERIODS.

BEACHLER

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 20Z...

* LOW POSSIBLITY OF ISOLATED SHRA/TSRA THIS AFTERNOON

KMD

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

STORMS TO THE SOUTHEAST OF THE TERMINALS ARE IN A WEAKENING
PHASE...BUT ARE SENDING AN OUTFLOW NORTHWARD. LITTLE ACTIVITY IS
OCCURRING ALONG THE OUTFLOW FARTHER NORTH...THOUGH WE ARE SEEING
SOUTHERLY WINDS GUSTING TO THE UPPER TEENS AND SOME BRIEF MVFR
CIGS. CLEARING BEHIND THE OUTFLOW SUGGESTS THIS WILL NOT LAST
LONG...BUT THE ATMOSPHERE IN NE AND NC ILLINOIS IS MOIST AND
PRETTY UNSTABLE...SO EXPECT AT LEAST SCATTERED CUMULUS THIS
AFTERNOON. WINDS SHOULD FALL BACK TO A STEADIER SSW WIND IN THE
LOWER TEENS.

WITH THE UNSTABLE ENVIRONMENT IN PLACE...MODEL GUIDANCE IS MIXED
IN ADDITIONAL CONVECTIVE DEVELOPMENT THIS AFTERNOON. THERE IS NO
REAL TRIGGER IN WATER VAPOR IMAGERY AND THE UPPER LOW TRIGGERING
THIS MORNINGS ACTIVITY IS MOVING EAST...SO HAVE HELD ONTO DRY
TAFS AS ANYTHING THAT GOES WOULD NEED TO BE TRIGGERED BY SUBTLE
FORCING. NO REAL IMPACTS TONIGHT OTHER THAN SOME PATCHY FOG.

SHORTWAVE ENERGY TO THE WEST MOVES OVERHEAD ON WEDNESDAY...THOUGH
SOUNDINGS ARE LARGELY DRY. A WEAKENING LOW LEVEL WIND FIELD
SUGGESTS A LAKE BREEZE DEVELOPS...BUT AT THIS POINT CONFIDENCE IS
NOT HIGH THAT IS GETS WEST OF THE LAKESHORE AREAS.

KMD

//ORD AND MDW CONFIDENCE...UPDATED 20Z...

* MEDIUM-HIGH THAT TERMINALS REMAIN DRY THIS AFTERNOON.
* HIGH WITH WIND SPEED AND DIRECTION

KMD

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

WEDNESDAY NIGHT...VFR.

THURSDAY...VFR.

FRIDAY...VFR.

SATURDAY...VFR.

SUNDAY...VFR.

MONDAY...SLIGHT CHANCE OF TSRA.

RODRIGUEZ

&&

.MARINE...
230 PM CDT

HIGH PRESSURE WILL REMAIN OVER THE EASTERN OHIO
VALLEY...ALLOWING SOUTHERLY TO AT TIMES SOUTHWESTERLY FLOW ACROSS
LAKE MICHIGAN. A WEAK FRONTAL BOUNDARY WILL TRY TO PUSH SOUTH ACROSS
FAR NORTHERN LAKE MICHIGAN AND TURN WINDS NORTHERLY...BUT THEN TURN
SOUTH AGAIN LATE IN THE WEEK. THE GRADIENT WILL REMAIN LIGHT...WHICH
WILL ALLOW FOR THE DEVELOPMENT OF AFTERNOON LAKE BREEZES. VERY WARM
AND MOIST AIR WILL CONTINUE TO FLOW ACROSS THE LAKE...AND COULD
ALLOW FOR PATCHY FOG TO REDEVELOP LATE TONIGHT. CURRENTLY WINDS ARE
JUST STRONG ENOUGH THAT THIS DOES NOT APPEAR TO BE FORMING. SO
CONFIDENCE IS CURRENTLY LOW.

BEACHLER

&&

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

$$

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