Severe Thunderstorm Warning 34, NWS Chicago, IL

AREA FORECAST DISCUSSION (GRIDS)
NATIONAL WEATHER SERVICE CHICAGO IL
145 AM CDT SUN SEP 29 2002

SHORT TERM:
SOUTHWEST FLOW TO DOMINATE BETWEEN WESTERN TROUGH AND STRONG EASTERN
RIDGE ALOFT.  UNSEASONABLE WARMTH THE MAIN MESSAGE NEXT SEVERAL DAYS.

STRONG THETA-E ADVECTION AT 850 OR SO CONTINUING TO REDEVELOP
SHOWERS AND THUNDERSTORMS FAR NORTHEAST IOWA...PROPAGATING ACROSS
FAR NORTHERN PART OF OUR CWFA JUST NORTH OF SURFACE WARM FRONT.
PER MODELS THIS PROCESS LIKELY TO CONTINUE UNTIL SUNRISE OR SO WITH
SHOWERS AND TSTORMS THEN MOVING OUT BY MIDDAY WITH WARM FRONT
SURGING/REDEVELOPING NORTH OF AREA. WILL GO CATEGORICAL SCATTERED
ACROSS FAR NORTH. CHANCE SOUTH TO I 80 AND WILL ELIMINATE THREAT
OVER MOST AREAS SOUTH OF ABOUT I 80.

AFTER THAT WARM MOIST AIR AT LOW LEVELS THIS AFTERNOON AND TONIGHT
WITH SOME DRYING SURFACE AND 850 MONDAY.  ANY CONVECTIVE THREAT IN
WARM SECTOR APPEARS CAPPED DESPITE SOME FAIRLY GOOD LOW LEVEL
INSTABILITY THIS AFTERNOON AND EVENING.

GOING TEMP FORECASTS TODAY IN LINE WITH MOS BLEND.  WILL BUMP UP TO
NEAR 85 SOUTHWEST PORTIONS.  FOR MONDAY...MOS BLEND A COUPLE DEGREES
WARMER THAN GOING FORECAST AND WILL ADJUST ACCORDINGLY.  DESPITE
PAST SUSPICIONS ABOUT ETA SURFACE TEMP PERFORMANCE WOULD NOT BE
SURPRISED IF IT WAS CORRECT MONDAY ON TEMPS NEAR 90 IN PARTS OF THE
AREA.

WITH LITTLE CLOUDINESS AND LITTLE TEMP CHANGE AT 850 MB...TUESDAY
NOT LIKELY TO BE MUCH COOLER THAN MONDAY AND WILL NUDGE TEMPS UP A
COUPLE DEGREES.

LONGER TERM...
TIMING OF FRONTS PASSAGE THROUGH OUR AREA IS QUESTIONABLE OFF
LATEST MODEL RUNS.  NONE OF THE MODELS PUSH IT THROUGH BEFORE
TUESDAY NIGHT. BERMUDA HIGH KEEPS PUSHING WEST THROUGH TUESDAY,
WHILE WESTERLY WAVE DRIVING FRONT IS WAY UP IN CANADA.  PRECIP
INDICATED AFTER MIDNIGHT TUESDAY AND ALL DAY WEDNESDAY STILL LOOKS
REASONABLE, ALTHOUGH PER AVN THREAT COULD DRAG ON INTO WEDNESDAY
NIGHT WITH FRONT, OR RESUME SOONER THAN FRIDAY DUE TO APPROACH
OF LOWER LATITUDE TROUGH FROM THE ROCKIES.  FOR NOW HOWEVER, WILL
LEAVE WEATHER AS IS...IE NO PRECIP WEDNESDAY NIGHT THROUGH THURSDAY
NIGHT AND LET ANOTHER RUN OF MODELS INCREASE CONFIDENCE IN TIMING
THAT FAR OUT.

ALSO...SHOULD BE MORE TEMPERATURE GRADIENT NORTH TO SOUTH ON
WEDNESDAY WITH SLOWER MOVEMENT OF FRONT.  WILL MAKE ADJUSTMENT
TOWARD WARMER TEMPS IN THE SOUTH.  NO OTHER CHANGES TO EXTENDED.

INTERESTINGLY, WITHOUT A LOT OF CONFIDENCE, MEDIUM RANGE MODELS ARE
SUGGESTING WE COULD GET AFFECTED EVENTUALLY BY RECURVING, AND THEN
EXTRATROPICAL, LILI LATE IN THE WEEK.

ISC GRIDS OUT BY AROUND 815Z.

.CHI...NONE

KAPLAN