

000 

WWUS20 KWNS 232013

SEL2

SPC WW 232013

INZ000-MIZ000-OHZ000-LEZ000-LHZ000-LMZ000-240300-



URGENT - IMMEDIATE BROADCAST REQUESTED

SEVERE THUNDERSTORM WATCH NUMBER 642

NWS STORM PREDICTION CENTER NORMAN OK

410 PM EDT THU AUG 23 2007



THE NWS STORM PREDICTION CENTER HAS ISSUED A

SEVERE THUNDERSTORM WATCH FOR PORTIONS OF



       NORTHERN INDIANA

       SOUTHERN LOWER MICHIGAN

       NORTHWEST OHIO

       LAKE ERIE

       LAKE HURON

       LAKE MICHIGAN



EFFECTIVE THIS THURSDAY AFTERNOON AND EVENING FROM 410 PM UNTIL

1100 PM EDT.



HAIL TO 2 INCHES IN DIAMETER...THUNDERSTORM WIND GUSTS TO 80

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



THE SEVERE THUNDERSTORM WATCH AREA IS APPROXIMATELY ALONG AND 90

STATUTE MILES NORTH AND SOUTH OF A LINE FROM 30 MILES WEST OF

BENTON HARBOR MICHIGAN TO 15 MILES EAST NORTHEAST OF MOUNT

CLEMENS MICHIGAN.  FOR A COMPLETE DEPICTION OF THE WATCH SEE THE

ASSOCIATED WATCH OUTLINE UPDATE (WOUS64 KWNS WOU2).



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 640...WW 641...



DISCUSSION...AN ISOLATED STRONG/SEVERE STORM HAS DEVELOPED OVER NE

OF GRR...WHILE UPSTREAM SEVERE MCS WITH MULTIPLE BOW ECHOES

CONTINUES TO MOVE ENEWD AROUND 50 KT.  ENVIRONMENT OVER THE WATCH

AREA IS MODERATELY UNSTABLE WITH MLCAPE OF 1500-2500 J/KG...AND

WSWLY UNDIRECTIONAL FLOW OF 35-45 KT ABOVE THE PBL IS PROVIDING

FAVORABLE VERTICAL SHEAR FOR MAINTENANCE OF SEVERE MCS INTO THE SRN

GREAT LAKES.  PRIMARY THREAT WILL BE FOR WIDESPREAD DAMAGING WINDS

ALTHOUGH ISOLATED HAIL AND A BRIEF TORNADO ARE ALSO

POSSIBLE...MAINLY ASSOCIATED WITH BOOKEND/MESOVORTICIES ALONG THE

BOW ECHOES AND DISCRETE ISOLATED CELLS THAT CAN FORM.



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

TO 2 INCHES. EXTREME TURBULENCE AND SURFACE WIND GUSTS TO 70

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

MOTION VECTOR 25050.





...WEISS

