Severe Thunderstorm Warning 142, NWS Chicago, IL

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO IL
545 AM CDT WED JUL 21 2004

.DISCUSSION...
FEW CHANGES WERE MADE TO THE INHERITED FCST AND WILL KEEP THIS
AFD BRIEF. INCREASED POPS FOR TODAY TO LIKELY AND CARRIED INTO
THE EVENING ACROSS THE SRN ZONES. ALSO INSERTED SVR WORDING
FOR TODAY. EARLY SPC DAY-1 ISSUANCE APPEARS TO REFLECT THE
UPCOMING DAY VERY WELL SO WILL NOT ENTIRELY REHASH THAT HERE.
WILL ONLY ADD THAT THE SVR CONCERNS FOR TODAY WILL BE HAIL...
WIND AND LOCALLY HEAVY RAIN AS THE G-R SMOTION OF THE TS WILL BE
SLOW UNTIL SUB-CLOUD LAYER COLD POOL GENERATION INDUCES AN
ACCELERATION ON THE FWD PROPAGATION. CONCERNING HIGH TEMPS...MAV
CONTINUES 90+ TREND WHILE THE ETA IS COOLER ASSOCIATED WITH TS
ACTIVITY. WILL STAY BELOW MAV BUT MAINTAIN HIGHS AT 90 WITH
CONTINUED 70+ DEWS. THEREFORE HEAT INDICES WILL REMAIN BELOW
CRITICAL THRESHOLDS.

MORE TSRA ON THR INTO THR NIGHT AHEAD OF A COLD FRONT. THE FRONT
SHOULD ENTER INTO THE NRN PORTION OF THE CWA LATE THR AFTERNOON
OR THR EVENING CLEARING THE CWA THAT NIGHT. A RELATIVELY COOL AND
DRY CONDITIONS APPEAR IN STORE FOR THE WEEKEND AND INTO NEXT
WEEK.

&&

.AVIATION DISCUSSION REGARDING 12Z TAFS...

AGAIN...PROSPECT FOR SEVERE STORMS THREATENS. TIMING IS THE
QUESTION. THUS WILL HAVE TO LEAVE THEM OUT OF TAFS...BUT WUD EXPECT
THEM TO BLOW UP INTO NRN IL/NWRN INDY THIS AFTN SOMETIME INTO THIS
EVENING. OTHERWISE WILL HAVE BKN AC WITH SOME SCT TO BKN AFTN CU
ARND 4K. SOME LIGHT FOG THIS AM AT RFD AND PSBLY AT DPA...CLEARING
TO AOA 6 MI BY 8AM. WINDS SOUTHWEST TODAY PICKING UP TO 10-15 KTS
AFTER NOON TIL SUNSET. MAY BE A LAKE BREEZE MOVING INLAND FOR A FEW
MILES NOT UNLIKE YDA. THIS BREEZE WITH WIND SHIFT TO EAST WAS NOT
REFLECTED AT TERMINALS YDA AND WILL NOT INPUT A SHIFT TO THE EAST
THIS AFTN EITHER. COOL FNT DROPPING DOWN TO NRN IL AFT MDNGT TONIGHT
SWITCHING WINDS TO WESTNORTHWEST. REAL COLDER AIR WILL BE DELAYED
UNTIL LATE THURSDAY WITH THREAT OF TSTMS REDEVELOPING THURSDAY AS
SECONDARY FNT NEARS.

RLB
&&

.LOT...WATCHES/WARNINGS/ADVISORIES...
.IL...NONE.
.IN...NONE.
.LK MI...NONE.

HAZARDOUS WEATHER OUTLOOK...CORRECTED
NATIONAL WEATHER SERVICE CHICAGO IL
400 AM CDT WED JUL 21 2004

ILZ003>006-008-010>014-019>022-023-032-033-039-INZ001-002-010-011-019-221100-
WINNEBAGO-BOONE-MCHENRY-LAKE IL-OGLE-LEE-DE KALB-KANE-DU PAGE-COOK-
LA SALLE-KENDALL-GRUNDY-WILL-KANKAKEE-LIVINGSTON-IROQUOIS-FORD-
LAKE IN-PORTER-NEWTON-JASPER-BENTON-
400 AM CDT WED JUL 21 2004

THIS PORTION OF THE HAZARDOUS WEATHER OUTLOOK IS FOR NORTH CENTRAL
AND NORTHEAST ILLINOIS...AND NORTHWEST INDIANA.

.DAY ONE... TODAY AND TONIGHT

SEVERE THUNDERSTORMS ARE LIKELY TODAY AND THIS EVENING. A LARGE COMPLEX OF
THUNDERSTORMS WILL MOVE EAST OUT OF NORTHEAST IOWA INTO NORTHERN ILLINOIS LATER
THIS MORNING. FOR NORTHERN ILLINOIS...THE LEADING EDGE OF THE COMPLEX WILL BE
CAPABLE OF PRODUCING DAMAGING WINDS AND LOCALLY LARGE RAINFALL AMOUNTS...
PRIMARILY NORTH OF INTERSTATE 80. AS THE COMPLEX MOVES EAST INTO NORTHEAST
ILLINOIS IT WILL PRODUCE AN OUTFLOW BOUNDARY. THIS BOUNDARY WILL SERVE AS A
FOCUS FOR RENEWED THUNDERSTORM DEVELOP INTO THE AFTERNOON...PRIMARILY ALONG AND
SOUTH OF INTERSTATE 88. LARGE HAIL..LOCALLY LARGE RAINFALL AMOUNTS AND DAMAGING
WINDS WILL BE THE MAIN CONCERNS. THE AFTERNOON ACTIVITY SHOULD TAPER OFF FROM
WEST TO EAST THIS EVENING.

IN NORTHWEST INDIANA THE THUNDERSTORM COMPLEX SHOULD NOT ARRIVE UNTIL LATE
MORNING OR EARLY AFTERNOON. THE LATER ARRIVAL WILL ALLOW FOR ADDITIONAL DAYTIME
HEATING WHICH WILL ENHANCE ATMOSPHERIC DESTABILIZATION. THE ADDED INSTABILITY
WILL CONTRIBUTE TO A VERY LARGE HAIL AND DAMAGING WIND THREAT. LOCALLY LARGE
RAINFALL AMOUNTS ARE ALSO ANTICIPATED.

.DAYS TWO THROUGH SEVEN... THURSDAY THROUGH TUESDAY

THURSDAY AFTERNOON SHOULD SEE MORE THUNDERSTORMS AHEAD OF A COLD FRONT
THAT WILL ARRIVE IN THE REGION THURSDAY EVENING. AFTER THURSDAY...THE
REGION SHOULD REMAIN DRY AND RELATIVELY COOL THROUGH THE WEEKEND AND
INTO EARLY NEXT WEEK.

.SPOTTER INFORMATION STATEMENT...

SPOTTER ACTIVATION WILL LIKELY BE NEEDED LATER TODAY AND TONIGHT.

&&

COMPLETE FORECAST INFORMATION IS AVAILABLE ON THE
NWS CHICAGO WEBPAGE: WWW.CRH.NOAA.GOV/LOT (LOWER CASE)

LMZ740>746-766-221100-
WINTHROP HARBOR IL TO NEW BUFFALO MI-
LAKE MICHIGAN-
400 AM CDT WED JUL 21 2004

THIS PORTION OF THE HAZARDOUS WEATHER OUTLOOK IS FOR THE ILLINOIS
AND INDIANA WATERS OF LAKE MICHIGAN.

.DAY ONE... TODAY AND TONIGHT

PERIODS OF THUNDERSTORMS ARE EXPECTED LATER TODAY AND INTO THE EVENING.
LOCALLY VERY HEAVY RAINFALL RATES...FREQUENT CLOUD TO GROUND LIGHTING...HAIL
AND GUSTY WINDS ARE POSSIBLE THE STORMS.

.DAYS TWO THROUGH SEVEN... THURSDAY THROUGH TUESDAY

THURSDAY AFTERNOON SHOULD SEE MORE THUNDERSTORMS AHEAD OF A COLD FRONT
THAT WILL ARRIVE IN THE REGION THURSDAY EVENING. AFTER THURSDAY...THE
REGION SHOULD REMAIN DRY AND RELATIVELY COOL THROUGH THE WEEKEND AND
INTO EARLY NEXT WEEK.

&&

COMPLETE FORECAST INFORMATION IS AVAILABLE ON THE
NWS CHICAGO WEBPAGE: WWW.CRH.NOAA.GOV/LOT (LOWER CASE)