

471 

WWUS20 KWNS 190431

SEL3

SPC WW 190431

ILZ000-INZ000-MIZ000-WIZ000-LMZ000-191200-



URGENT - IMMEDIATE BROADCAST REQUESTED

SEVERE THUNDERSTORM WATCH NUMBER 473

NWS STORM PREDICTION CENTER NORMAN OK

1130 PM CDT THU JUN 18 2009



THE NWS STORM PREDICTION CENTER HAS ISSUED A

SEVERE THUNDERSTORM WATCH FOR PORTIONS OF



       NORTHEAST ILLINOIS

       NORTHWEST INDIANA

       SOUTHWEST LOWER MICHIGAN

       SOUTHEAST WISCONSIN

       LAKE MICHIGAN



EFFECTIVE THIS THURSDAY NIGHT AND FRIDAY MORNING FROM 1130 PM

UNTIL 700 AM 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 110

STATUTE MILES EAST AND WEST OF A LINE FROM 60 MILES NORTH OF

MILWAUKEE WISCONSIN TO 15 MILES SOUTHWEST OF VALPARAISO INDIANA.

FOR A COMPLETE DEPICTION OF THE WATCH SEE THE ASSOCIATED WATCH

OUTLINE UPDATE (WOUS64 KWNS WOU3).



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 470...WW 471...WW 472...



DISCUSSION...CLUSTER OF SEVERE STORMS OVER SRN WI WILL LIKELY

PERSIST AND SPREAD EWD/SEWD OVERNIGHT AS A FEED OF UNSTABLE AIR IS

MAINTAINED FROM THE W/SW ON A 35 KT LLJ.  THE PRIMARY SEVERE THREAT

ACROSS SW LOWER MI SHOULD BE LARGE HAIL WITH ELEVATED STORMS.  THE

THREAT FOR LARGE HAIL AND DAMAGING WINDS WILL BE GREATER FROM SE WI

INTO NE IL AND NW INDIANA...ESPECIALLY IF STORM MERGERS LEAD TO

UPSCALE GROWTH OF A COLD POOL AND MORE SEWD PROPAGATION OF THE

CLUSTER.



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 29025.





...THOMPSON

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