Area Forecast Discussion
Issued by NWS Chicago, IL

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000
FXUS63 KLOT 031959
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
259 PM CDT THU SEP 3 2015

.SHORT TERM...
254 PM CDT

THROUGH SATURDAY...

MAIN FORECAST CONCERNS OVER THE NEXT COUPLE DAYS WILL BE CONTINUED
UNSEASONABLY WARM AND HUMID CONDITIONS...AS WELL AS PRECIPITATION
CHANCES.

THIS AFTERNOON...SATELLITE IMAGERY AND SURFACE OBS SHOW A WEAK
TROUGH DRAPED FROM NEAR LSE THROUGH MSN AND MKE AND ACROSS LAKE
MICHIGAN. THIS TROUGH WILL CONTINUE TO SAG SOUTH THE THE REMAINDER
OF THE AFTERNOON AND INTO THE EVENING WITH WINDS TURNING FROM WEST-
SOUTHWEST AHEAD TO NORTHEAST BEHIND. THIS BOUNDARY IS EXPECTED TO
ENHANCE/BECOME COUPLED WITH A LAKE BREEZE THIS AFTERNOON WHICH
SHOULD HELP PUSH TEMPERATURES BACK INTO THE 70S ALONG THE LAKE
FRONT. THE BOUNDARY COULD ALSO SERVE AS THE FOCUS FOR
ISOLATED/WIDELY SCATTERED THUNDERSTORM DEVELOPMENT. LATEST SPC MESO-
ANALYSIS PAGE SHOWS AXIS OF MODERATELY STRONG INSTABILITY ACROSS
NORTHERN ILLINOIS...WEAKLY CAPPED OR UNCAPPED...HOWEVER LACK OF ANY
FORCING AND WEAK MIDLEVEL HEIGHT RISES APPEAR TO BE KEEPING
CONVECTION IN CHECK FOR THE MOMENT. AS THE AFOREMENTIONED TROUGH
MOVES INTO THE AREA THIS EVENING...IT SHOULD BE SUFFICIENT TO KICK
OF A FEW THUNDERSTORMS THOUGH CHANCES WILL THEN BEGIN TO DIMINISH
LATE THIS EVENING AS THE BOUNDARY LAYER BEGINS TO STABILIZE
NOCTURNALLY. WITH THE BOUNDARY IN PLACE...ISOLATED DEVELOPMENT MAY
LINGER OVERNIGHT...BUT NOT EXPECTING MUCH COVERAGE.

FOR FRIDAY...

TROUGH AXIS SETTLES OVER THE AREA ON FRIDAY WITH FAIRLY WEAK FLOW AT
THE SURFACE. LOW PRESSURE OVER THE PLAINS WILL ADVANCE EASTWARD WITH
MODEST WAA SPREADING INTO PORTIONS OF NORTHERN ILLINOIS. ALSO...A
LAKE BREEZE FORMS IN THE AFTERNOON. ANOTHER WARM AND HUMID DAY IS
ON TAP...THUS AN UNSTABLE ENVIRONMENT WILL DEVELOP AGAIN. GUIDANCE
IS MIXED WITH CONVECTIVE DEVELOPMENT...BUT HAVE LEANED AWAY FROM
THE MORE AGRESSIVE GUIDANCE AT THIS POINT...AND HAVE KEPT THE
HIGHEST POPS...STILL IN THE CHANCE CATEGORY...FOR THE LATER
AFTERNOON ALONG THE LAKE BREEZE.

BMD

&&

.LONG TERM...
310 AM CDT

FRIDAY NIGHT THROUGH WEDNESDAY...

UPPER RIDGE LOOKS TO FLEX A BIT MORE NORTHEAST INTO THE REGION OVER
THE WEEKEND AND WHILE ISOLATED STORMS CANNOT TOTALLY BE RULED
OUT...CHANCES LOOK SLIME WITH SATURDAY AND SUNDAY GENERALLY LOOKING
MAINLY RAIN FREE AT THIS POINT. TEMPERATURES LOOKS TO REMAIN VERY
WARM TO BORDERLINE HOT AND CONTINUED HUMID. HIGHS SHOULD EASILY
CLIMB INTO THE UPPER 80S WITH LOW 90S CERTAINLY POSSIBLE. LAKE
BREEZE IS POSSIBLE SATURDAY BUT LOOKS LESS LIKELY AT THIS POINT ON
SUNDAY.

COLD FRONT SHOULD BEGIN TO APPROACH FROM THE NORTHWEST SUNDAY NIGHT
OR MONDAY. IN GENERAL...MEDIUM RANGE GUIDANCE HAS SPED UP THE FRONT
SOME COMPARED TO RUNS 24 HOURS AGO. NOT CONVINCED IT WILL BE THIS
QUICK AND WORRIED THAT BLENDED MODEL HIGHS IN THE MID 80S MONDAY MAY
END UP BEING A BIT TOO COOL...BUT GIVEN RECENT MODEL TRENDS DIDNT
MAKE ANY CHANGES AT THIS POINT. IT DOES APPEAR AS THOUGH WE COULD
GET A BREAK FROM THE LATE RESURGENCE OF SUMMER BY THE MIDDLE OF NEXT
WEEK WITH HIGHS RETURNING INTO THE 70S AGAIN.

IZZI

&&

.AVIATION...

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

* TSRA/SHRA POSSIBLE WITH INCREASING CHANCES LATER THIS AFTERNOON
  AND EVENING...WITH ISOLATED ACTIVITY LINGERING OVERNIGHT.

* ABRUPT WIND SHIFT TO AN NNE DIRECTION LATE THIS AFTERNOON OR EARLY
  EVENING WITH WINDS ABOVE 10 KT POSSIBLE FOR A BRIEF TIME.

* MVFR CIGS/VIS THIS EVENING.

KMD

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

DESTABILIZATION CONTINUES ACROSS THE AREA THIS AFTERNOON WITH A BIT
MORE WIDESPREAD CUMULUS DEVELOPMENT ONGOING. SW WINDS ARE STRONG
ENOUGH TO KEEP A LAKE BREEZE AT BAY FOR THIS AFTERNOON...BUT
ATTENTION SHIFTS TO SOUTHWARD MOVING FRONTAL BOUNDARY MAKING DECENT
HEADWAY DOWN THE WESTERN SHORE OF LAKE MICHIGAN. WINDS SHIFT TO AN
NNE DIRECTION BEHIND THIS BOUNDARY...AND TO THIS POINT WINDS HAVE
LARGELY HELD UNDER 10 KT. THIS SHOULD LARGELY BE THE TREND AS THE
BOUNDARY MOVES SOUTH LATER THIS AFTERNOON AND EVENING...THOUGH A
BRIEF PERIOD OF WINDS IN EXCESS OF 10 KT ARE POSSIBLE.

OTHER CONCERN IS WITH CONVECTION ALONG THE LAKE BREEZE/FRONT AS LOW
PRESSURE IN NORTHWEST WISCONSIN MOVES SOUTH. SOME GUIDANCE IS TRYING
TO BREAK OUT SHOWERS THIS AFTERNOON...WHICH IS CERTAINLY POSSIBLE
GIVEN THE UNSTABLE ENVIRONMENT...BUT WITH THE FRONT/UPPER LOW NOT
ARRIVING UNTIL LATER THIS AFTERNOON AND EVENING...THIS STILL APPEARS
TO BE THE BEST FOCUS FOR THUNDERSTORMS. TIMING CONFIDENCE IS ONLY
MEDIUM AT THIS POINT...AND COVERAGE CONCERNS PRECLUDES MORE THAN A
VCTS MENTION AS WELL. MVFR CLOUDS WILL ACCOMPANY THE WIND
SHIFT...WITH AT LEAST A PERIOD OF BROKEN CIGS THROUGH THE
EVENING....POSSIBLY LONGER.

THE BOUNDARY WILL LINGER OVER THE AREA IN THE OVERNIGHT HOURS...AND
ENERGY ON THE BACK SIDE OF THE UPPER LOW CENTER IN MICHIGAN WHICH
WILL STALL OUT WILL MEAN ISOLATED DEVELOPMENT MAY CONTINUE
OVERNIGHT. CONFIDENCE IN COVERAGE IS LOW...THUS THE DRY TAF
FORECAST FOR OVERNIGHT.

KMD

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

* LOW-MEDIUM WITH TSRA/SHRA CHANCES/COVERAGE THROUGH THIS EVENING.
  MEDIUM ON TIMING.

* MEDIUM-HIGH WITH WIND SPEED/DIRECTION...MEDIUM ON TIMING OF WIND
  SHIFT AND IF IT WILL STAY UNDER 10 KT WHEN IT OCCURS.

* LOW ON MVFR CLOUDS FORMING THIS EVENING AND IF SO HOW LONG THEY
  LAST.

KMD

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

FRIDAY NIGHT...VFR.

SATURDAY...SLIGHT CHANCE OF TSRA.

SUNDAY...CHANCE OF TSRA LATE.

MONDAY...CHANCE OF TSRA.

TUESDAY...SLIGHT CHANCE OF TSRA.

WEDNESDAY...CHANCE OF TSRA.

RODRIGUEZ

&&

.MARINE...
428 AM CDT

AS A BOUNDARY REMAINS SITUATED ACROSS THE NORTHERN PORTIONS OF
THE LAKE THIS MORNING...A VARYING WIND FIELD IS OCCURRING ACROSS
THE LAKE. OVER THE NORTH...EAST NORTHEAST WINDS ARE OCCURRING AND
ACROSS THE SOUTH...SOUTHWEST WINDS ARE BEING OBSERVED. THIS WILL
LIKELY PERSIST FOR MOST OF TODAY...BUT WITH THE SOUTHWEST WINDS
ACROSS THE SOUTHERN PART OF LAKE TURNING MORE SOUTHEAST THIS
AFTERNOON. INCREASED WINDS OVER THE NORTH HALF TO 10 TO 20 KT FOR
THIS MORNING BUT HAVE THEM DIMINISHING IN THE AFTERNOON.
HOWEVER...DO THINK ITS POSSIBLE THAT 10 TO 20 KT WINDS COULD STILL
BE POSSIBLE IN THE AFTERNOON. WAVES SHOULD STAY CONFINED TO 1 TO 3
FEET TODAY AND TONIGHT BUT WITH THUNDERSTORMS PUSHING OVER THE
LAKE EARLY THIS MORNING...ASSOCIATED HIGHER WINDS COULD HELP TO
BRIEFLY BUILD THESE WAVES.

RODRIGUEZ

&&

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

$$

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