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ILZ000-INZ000-MIZ000-OHZ000-LEZ000-LHZ000-LMZ000-040400-



URGENT - IMMEDIATE BROADCAST REQUESTED

SEVERE THUNDERSTORM WATCH NUMBER 829

NWS STORM PREDICTION CENTER NORMAN OK

405 PM EDT SAT SEP 3 2011



THE NWS STORM PREDICTION CENTER HAS ISSUED A

SEVERE THUNDERSTORM WATCH FOR PORTIONS OF



       NORTHERN AND CENTRAL ILLINOIS

       NORTHERN INDIANA

       SOUTHERN LOWER MICHIGAN

       EXTREME NORTHWEST OHIO

       LAKE ERIE

       LAKE HURON

       LAKE MICHIGAN



EFFECTIVE THIS SATURDAY AFTERNOON FROM 405 PM UNTIL MIDNIGHT EDT.



HAIL TO 1.5 INCHES IN DIAMETER...THUNDERSTORM WIND GUSTS TO 70

MPH...AND DANGEROUS LIGHTNING ARE POSSIBLE IN THESE AREAS.



THE SEVERE THUNDERSTORM WATCH AREA IS APPROXIMATELY ALONG AND 45

STATUTE MILES NORTH AND SOUTH OF A LINE FROM 40 MILES SOUTH

SOUTHWEST OF MOLINE ILLINOIS TO 20 MILES EAST OF MOUNT CLEMENS

MICHIGAN.  FOR A COMPLETE DEPICTION OF THE WATCH SEE THE

ASSOCIATED WATCH OUTLINE UPDATE (WOUS64 KWNS WOU9).



REMEMBER...A SEVERE THUNDERSTORM WATCH MEANS CONDITIONS ARE

FAVORABLE FOR SEVERE THUNDERSTORMS IN AND CLOSE TO THE WATCH

AREA. PERSONS IN THESE AREAS SHOULD BE ON THE LOOKOUT FOR

THREATENING WEATHER CONDITIONS AND LISTEN FOR LATER STATEMENTS

AND POSSIBLE WARNINGS. SEVERE THUNDERSTORMS CAN AND OCCASIONALLY

DO PRODUCE TORNADOES.



OTHER WATCH INFORMATION...CONTINUE...WW 828...



DISCUSSION...LARGE-SCALE ASCENT SPREADING AHEAD OF BOTH A

SUB-SYNOPTIC WAVE OVER THE CORN BELT AND A PRIMARY MID-LVL WAVE

SPREADING ACROSS THE UPR GRTLKS REGION WILL RESULT IN UPSCALE GROWTH

OF TSTMS ACROSS THE REGION LATE THIS AFTN/EVE.  STORMS WILL LIKELY

FAVOR A CORRIDOR VCNTY OLD OUTFLOW BOUNDARY FROM SERN LWR MI SWWD

INTO NRN IL.  HERE...SRN FRINGE OF LARGELY UNIDIRECTIONAL 30-40 KTS

OF MID-LVL FLOW WILL RESULT IN KINEMATIC ENVIRONMENT CONDUCIVE FOR

BOWS AND BRIEF SUPERCELL STRUCTURES...ESPECIALLY GIVEN 2500-3000

J/KG OF MLCAPE.  DMGG WIND GUSTS AND LARGE HAIL WILL BE LIKELY.



AVIATION...A FEW SEVERE THUNDERSTORMS WITH HAIL SURFACE AND ALOFT

TO 1.5 INCHES. EXTREME TURBULENCE AND SURFACE WIND GUSTS TO 60

KNOTS. A FEW CUMULONIMBI WITH MAXIMUM TOPS TO 500. MEAN STORM

MOTION VECTOR 24035.





...RACY

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