Flash Flood Warning 9, NWS Chicago, IL

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO IL
630 AM CDT SUN JUL 27 2003

AVIATION DISCUSSION FOR 12Z TAFS

AT 10Z FRONT FROM NR MTTW-DBQ-S DSM. FRONT SHOULD PASS THRU CHI
TERMINALS BETWEEN 17-19Z WITH COUPLE HOURS EARLIER AT RFD. SO FAR
NOTHING BUT SOME CLOUDS ALONG FRONT AS CAP STILL HOLDING. ALL MODLES
SHOW VERY RAPID DESTABILIZATION BY 18Z WITH CAP GONE. THE MAIN Q IS
WILL TS DEVELOP AS FRONT IS MOVING THRU CHI OR JUST TO S. LOOKS LIKE
MOST LIKELY JUST S OF THE AIRPORTS BUT A VERY CLOSE CALL. THE LAKE
BREEZE BEHIND THE FRONT MIIGHT BE THE ADDED PUSH TO GET THINGS GOING
AS EVEN AT 10Z SPC MESO DATA SHOWS CAPES AOA 2500 IN AREA AND PRECIP
H2O ABOVE 1.8 INCHES. SO THE ONLY Q IS THE TIME OF INITIATION WHICH
SHOULD BE IN THE 17-19Z TIME FRAME. ONCE FRONT GOES THRU WINDS TURN
IN OFF LAKE. STILL EXPECT VFR CONDS AS LAKE TOO WARM TO INFLUENCE
ANY LO CLOUDS. WITH ALL THIS IN MIND WILL CARRY A VCTS IN CHI TAFS
FOR 2 HOURS SINCE CAN NOT CARRY PROB GROUP 1ST 9 HOURS AND NOT
ENOUGH CONFIDENCE TO HAVE A TEMPO GROUP.

AF

WEAK SURFACE FRONT APPEARS TO BE FROM ABOUT THE STRAIGHTS OF MAC TO
JUST N OF DSM AT 06Z. NW SURFACE WINDS WEAK BEHIND FRONT AND
PRESSURE RISES MINIMAL...SO NOT A REAL STRONG PUSH BEHIND IT. BAND
OF MID CLOUDS IN IR SATELLITE LOOP IS ALL THATS GOING ON ATTM AS AMS
IS STILL QUITE CAPPED AND BEST DYNAMICS WELL NORTH ACROSS SOUTHERN
CANADA. MID 70S DEWPOINTS HAVE POOLED AHEAD AND ALONG FRONT ACROSS
IOWA AND SRN WIS. WITH LITTLE CLOUD COVER TEMPS SHOULD CLIMB QUICKLY
THIS MORNING INTO MID 80S...AND MAY TOP SATURDAYS MAXES. AMS WILL
BECOME FAIRLY UNSTABLE WITH CAPES 2000 TO 2500 BUT STILL QUITE WARM
ALOFT AND CONVERGENCE AND UPPER SUPPORT WILL BE WEAK. FRONT MAY SLIP
THROUGH RFD AND CHI QUIETLY THIS MORNING BUT THUNDERSTORMS SHOULD
ERUPT OVER SOUTHER PART OF FORECAST AREA...MAINLY S OF 1-80 IN THE
AFTERNOON AND CONTINUE THROUGH EVENING. LAKE BREEZE MAY ADD TO
CONVERGENCE W AND S OF CHICAGO. MAIN THREAT NOW APPEARS TO BE HEAVY
RAIN IN VERY MOIST ENVIRONMENT WITH WEAK SHEAR.

A LITTLE CONCERNED ABOUT POSSIBILITY OF INSTABILITY SHOWERS MONDAY
AFTERNOON AS AREA WILL STILL BE UNDER THE INFLUENCE OF ERN CANADA
UPPER LOW AND POCKET OF -10 TO -12 AIR AT H5 OVER THE AREA. GUIDANCE
TEMPS LOOK GOOD MONDAY WITH SOME LAKE COOLING.

DRY AND PLEASANT TUESDAY. SW FLOW DEVELOPING AHEAD OF APPROACHING
SYSTEM FROM THE NW SO MINIMLA LAKE COOLING IF ANY. THEN UPPER LOW
DROPS IN WED. NEW MRF CREEPS LOW SLOWLY ACROSS THE GREAT LAKES THU
AND FRI. BASED ON THIS WILL ADD DIURNAL CLOUDS AND CHANCE OF
AFTERNOON SHOWERS AND THUNDERSTORMS INTO FRI. WILL KEEP THE WEEKEND
DRY FOR NOW. TEMPS SHOULD ALSO BE COOL THU UNDER THE INFLUENCE OF
THE COOL POOL BUT MODIFYING BY THE WEEKEND.

.CHI...NONE.

ALLSOPP

ILZ003>006-008-010>014-019-020>023-032-033-039-INZ001-002-010-011-019
-281100-

HAZARDOUS WEATHER OUTLOOK...UPDATED
NATIONAL WEATHER SERVICE CHICAGO IL
820 AM CDT SUN JUL 27 2003

THIS HAZARDOUS WEATHER OUTLOOK IS FOR NORTH CENTRAL AND NORTHEAST
ILLINOIS...NORTHWEST INDIANA...AND THE ADJACENT WATERS OF LAKE
MICHIGAN.

.DAY ONE... TODAY AND TONIGHT

THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS THIS AFTERNOON AND
THIS EVENING ALONG AND SOUTH OF THE INTERSTATE 80 CORRIDOR.
SCATTERED THUNDERSTORMS ARE EXPECTED TO DEVELOP ALONG A WEAK...SLOW
MOVING COLD FRONT BY THIS AFTERNOON AND CONTINUE THROUGH THIS
EVENING. THIS AREA OF DEVELOPMENT WILL BE MOST INTENSE ALONG AND
SOUTH OF INTERSTATE 80.

MORNING SUNSHINE WILL HEAT THE AIR WELL INTO THE 80S. THIS COMBINED
WITH DEWPOINTS IN THE LOWER TO MIDDLE 70S WILL DESTABILIZE THE
ATMOSPHERE. ALTHOUGH CONVERGENCE ALONG THE FRONT WILL NOT BE VERY
STRONG...THE LAKE BREEZE MAY ENHANCE CONVERGENCE WEST AND SOUTH OF
CHICAGO AND IN NORTHWEST INDIANA. SOME OF THE STORMS MAY PRODUCE
LARGE HAIL AND DAMAGING WINDS...ALONG WITH ALWAYS DANGEROUS
LIGHTNING...AND HEAVY RAIN WHICH WILL LIKELY BE ENOUGH TO CAUSE
LOCALIZED FLOODING.

.DAYS TWO THROUGH SEVEN... MONDAY THROUGH SATURDAY

THERE IS A CHANCE OF THUNDERSTORMS WEDNESDAY AFTERNOON THROUGH
FRIDAY AFTERNOON.

.SPOTTER INFORMATION STATEMENT...

SPOTTERS MAY BE NEEDED THIS AFTERNOON AND EVENING.

&&

           NWS CHICAGO WEBPAGE

    HTTP://WWW.CRH.NOAA.GOV/LOT (LOWER CASE)
OR  HTTP://WEATHER.NOAA.GOV/CHICAGO (LOWER CASE)

RLB