WATCHES: Severe Thunderstorm Watch Number 688

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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