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000 

WWUS20 KWNS 042151

SEL6

SPC WW 042151

IAZ000-ILZ000-WIZ000-LMZ000-050500-



URGENT - IMMEDIATE BROADCAST REQUESTED

SEVERE THUNDERSTORM WATCH NUMBER 806

NWS STORM PREDICTION CENTER NORMAN OK

450 PM CDT MON AUG 4 2008



THE NWS STORM PREDICTION CENTER HAS ISSUED A

SEVERE THUNDERSTORM WATCH FOR PORTIONS OF



       EAST CENTRAL IOWA

       NORTHERN ILLINOIS

       SOUTHEAST WISCONSIN

       LAKE MICHIGAN



EFFECTIVE THIS MONDAY AFTERNOON FROM 450 PM UNTIL MIDNIGHT CDT.



HAIL TO 2 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 50

STATUTE MILES NORTH AND SOUTH OF A LINE FROM 35 MILES WEST

SOUTHWEST OF CEDAR RAPIDS IOWA TO 65 MILES EAST OF ROCKFORD

ILLINOIS.  FOR A COMPLETE DEPICTION OF THE WATCH SEE THE

ASSOCIATED WATCH OUTLINE UPDATE (WOUS64 KWNS WOU6).



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.



DISCUSSION...THUNDERSTORM CLUSTER NOW FORMING OVER E CENTRAL IA WILL

LIKELY EXPAND/INTENSIFY THROUGH THIS EVENING AS IT MOVES EWD AND

ENCOUNTERS AND ENVIRONMENT OF STRONG INSTABILITY.  STEEP LAPSE RATES

AND STRONG INSTABILITY...IN CONJUNCTION WITH STORM MERGERS/

INTERACTIONS ...SHOULD LEAD TO UPSCALE GROWTH AND COLD POOL

FORMATION...WITH AN ATTENDANT THREAT FOR DAMAGING WINDS.  VERTICAL

SHEAR AND INSTABILITY ARE ALSO SUFFICIENT FOR SUPERCELLS AND PERHAPS

AN ISOLATED TORNADO...THOUGH THE EARLY CONVECTIVE MODE EVOLUTION

APPEARS TO FAVOR CLUSTERS OVER ISOLATED STORMS.



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

TO 2 INCHES. EXTREME TURBULENCE AND SURFACE WIND GUSTS TO 60

KNOTS. A FEW CUMULONIMBI WITH MAXIMUM TOPS TO 550. MEAN STORM

MOTION VECTOR 28035.





...THOMPSON

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