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896 

WWUS20 KWNS 042229

SEL7

SPC WW 042229

ILZ000-INZ000-MIZ000-OHZ000-LEZ000-LMZ000-050400-



URGENT - IMMEDIATE BROADCAST REQUESTED

SEVERE THUNDERSTORM WATCH NUMBER 257

NWS STORM PREDICTION CENTER NORMAN OK

630 PM EDT FRI JUN 4 2010



THE NWS STORM PREDICTION CENTER HAS ISSUED A

SEVERE THUNDERSTORM WATCH FOR PORTIONS OF



       NORTHEAST ILLINOIS

       NORTHERN INDIANA

       SOUTHERN LOWER MICHIGAN

       EXTREME NORTHWEST OHIO

       LAKE ERIE

       LAKE MICHIGAN



EFFECTIVE THIS FRIDAY NIGHT FROM 630 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 55

STATUTE MILES NORTH AND SOUTH OF A LINE FROM 20 MILES NORTH

NORTHEAST OF DETROIT MICHIGAN TO 30 MILES SOUTHWEST OF MARSEILLES

ILLINOIS.  FOR A COMPLETE DEPICTION OF THE WATCH SEE THE

ASSOCIATED WATCH OUTLINE UPDATE (WOUS64 KWNS WOU7).



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 254...WW 255...WW 256...



DISCUSSION...WIDELY SCATTERED THUNDERSTORMS WILL CONTINUE TO FORM IN

A BROKEN BAND FROM NE IL ACROSS NW INDIANA TO SRN LOWER MI.  THOUGH

INSTABILITY IS NOT PARTICULARLY STRONG /ESPECIALLY WHERE CLOUDS HAVE

LIMITED SURFACE HEATING ACROSS NRN INDIANA AND SE LOWER

MI/...DEEP-LAYER VERTICAL SHEAR IS SUFFICIENT FOR SUPERCELLS.

ADDITIONALLY...A WEAK MID-UPPER SPEED MAX MOVING EWD TOWARD NRN IL

FROM ERN IA MAY HELP CONDITION THE BACKGROUND ENVIRONMENT AND FAVOR

THE FORMATION OF A FEW MORE STORMS THIS EVENING.  DAMAGING WINDS

WILL BE THE PRIMARY SEVERE THREAT...ALONG WITH ISOLATED LARGE HAIL.



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 28030.





...THOMPSON

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