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149 

WWUS20 KWNS 092148

SEL8

SPC WW 092148

INZ000-MIZ000-LHZ000-LMZ000-100500-



URGENT - IMMEDIATE BROADCAST REQUESTED

SEVERE THUNDERSTORM WATCH NUMBER 688

NWS STORM PREDICTION CENTER NORMAN OK

550 PM EDT SUN AUG 9 2009



THE NWS STORM PREDICTION CENTER HAS ISSUED A

SEVERE THUNDERSTORM WATCH FOR PORTIONS OF



       EXTREME NORTHERN INDIANA

       CENTRAL AND SOUTHERN LOWER MICHIGAN

       LAKE HURON

       LAKE MICHIGAN



EFFECTIVE THIS SUNDAY AFTERNOON AND MONDAY MORNING FROM 550 PM

UNTIL 100 AM 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 75

STATUTE MILES NORTH AND SOUTH OF A LINE FROM 50 MILES WEST

NORTHWEST OF BENTON HARBOR MICHIGAN TO 30 MILES EAST NORTHEAST OF

MOUNT CLEMENS MICHIGAN.  FOR A COMPLETE DEPICTION OF THE WATCH

SEE THE ASSOCIATED WATCH OUTLINE UPDATE (WOUS64 KWNS WOU8).



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 682...WW 683...WW

684...WW 685...WW 686...WW 687...



DISCUSSION...AIR MASS HAS QUICKLY RECOVERED FROM EARLY DAY TSTMS.

SFC TEMPERATURES WELL INTO THE 80S AND LWR 90S COUPLED WITH STEEP

LAPSE RATES AND VERY MOIST BOUNDARY LAYER HAVE CONTRIBUTED TO

MLCAPES 3000-4000 J/KG.  TSTMS UPSTREAM ACROSS WI AND SRN LWR MI ARE

EXPECTED TO CONTINUE MOVING EWD INTO THE REGION THIS EVENING.

VERTICAL SHEAR WAS SOMEWHAT WEAK...BUT DEEP WLY UNIDIRECTIONAL FLOW

/MEAN WIND 40 KTS/ AND MAGNITUDE OF INSTABILITY WILL BE FAVORABLE

FOR BOWING LINE SEGMENTS GIVING DMGG WINDS AND HAIL.



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 500. MEAN STORM

MOTION VECTOR 26035.





...RACY/EVANS

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