

000 

WWUS20 KWNS 230019

SEL9

SPC WW 230019

MIZ000-LMZ000-230500-



URGENT - IMMEDIATE BROADCAST REQUESTED

SEVERE THUNDERSTORM WATCH NUMBER 639

NWS STORM PREDICTION CENTER NORMAN OK

820 PM EDT WED AUG 22 2007



THE NWS STORM PREDICTION CENTER HAS ISSUED A

SEVERE THUNDERSTORM WATCH FOR PORTIONS OF



       SOUTHWEST AND CENTRAL LOWER MICHIGAN

       LAKE MICHIGAN



EFFECTIVE THIS WEDNESDAY NIGHT AND THURSDAY MORNING FROM 820 PM

UNTIL 100 AM 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 35

STATUTE MILES NORTH AND SOUTH OF A LINE FROM 15 MILES SOUTH OF

MUSKEGON MICHIGAN TO 15 MILES EAST OF FLINT MICHIGAN.  FOR A

COMPLETE DEPICTION OF THE WATCH SEE THE ASSOCIATED WATCH OUTLINE

UPDATE (WOUS64 KWNS WOU9).



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 637...WW 638...



DISCUSSION...A SMALL MCS OVER LAKE MI WILL MOVE INLAND OVER SW LOWER

MI AND CONTINUE EWD ALONG AN INSTABILITY GRADIENT INTO CENTRAL LOWER

MI THROUGH THE EARLY OVERNIGHT HOURS.  RESIDUAL STEEP LAPSE RATES IN

THE LOW LEVELS...ALONG WITH STRONG INSTABILITY AND 35-40 KT MOTION

OF THE COLD POOL...SHOULD SUPPORT A THREAT FOR DAMAGING WINDS GUSTS

FOR THE NEXT FEW HOURS.



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 27035.





...THOMPSON

