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WWUS20 KWNS 201741

SEL2

SPC WW 201741

MIZ000-LEZ000-LHZ000-210100-



URGENT - IMMEDIATE BROADCAST REQUESTED

SEVERE THUNDERSTORM WATCH NUMBER 792

NWS STORM PREDICTION CENTER NORMAN OK

140 PM EDT SAT AUG 20 2011



THE NWS STORM PREDICTION CENTER HAS ISSUED A

SEVERE THUNDERSTORM WATCH FOR PORTIONS OF



       SOUTHERN LOWER MICHIGAN

       LAKE ERIE

       LAKE HURON



EFFECTIVE THIS SATURDAY AFTERNOON AND EVENING FROM 140 PM UNTIL

900 PM 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 85

STATUTE MILES EAST AND WEST OF A LINE FROM 40 MILES SOUTHWEST OF

JACKSON MICHIGAN TO 30 MILES NORTH NORTHEAST OF FLINT 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.



DISCUSSION...A LINEAR CLUSTER OF THUNDERSTORMS IS MOVING EWD FROM

LAKE MI INTO SW LOWER MI.  THOUGH DOWNSTREAM ANVIL HAS LIMITED

SURFACE HEATING...SURFACE TEMPERATURES NEAR 80 AND DEWPOINTS NEAR 70

ARE STILL SUPPORTING MLCAPE AOA 2000 J/KG.  LOW-LEVEL FLOW IS NOT

PARTICULARLY STRONG OVER LOWER MI...BUT 40 KT WLY MIDLEVEL FLOW IS

CONTRIBUTING TO SUFFICIENT BULK SHEAR FOR ORGANIZED BOWING SEGMENTS

AND CLUSTERS.  A FEW DAMAGING GUSTS AND MARGINALLY SEVERE HAIL WILL

BE THE PRIMARY SEVERE THREATS THIS AFTERNOON AS THE CONVECTION

SPREADS EWD TOWARD SE LOWER MI.



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 27030.





...THOMPSON

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