

660 

WWUS20 KWNS 220004

SEL9

SPC WW 220004

MIZ000-LHZ000-LMZ000-220500-



URGENT - IMMEDIATE BROADCAST REQUESTED

SEVERE THUNDERSTORM WATCH NUMBER 679

NWS STORM PREDICTION CENTER NORMAN OK

805 PM EDT TUE SEP 21 2010



THE NWS STORM PREDICTION CENTER HAS ISSUED A

SEVERE THUNDERSTORM WATCH FOR PORTIONS OF



       CENTRAL AND SOUTHERN LOWER MICHIGAN

       LAKE HURON

       LAKE MICHIGAN



EFFECTIVE THIS TUESDAY NIGHT AND WEDNESDAY MORNING FROM 805 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 60

STATUTE MILES NORTH AND SOUTH OF A LINE FROM 30 MILES EAST OF BAD

AXE MICHIGAN TO 30 MILES SOUTH SOUTHWEST OF MUSKEGON 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...THIS SEVERE THUNDERSTORM WATCH REPLACES

SEVERE THUNDERSTORM WATCH NUMBER 676. WATCH NUMBER 676 WILL NOT

BE IN EFFECT AFTER 805 PM EDT. CONTINUE...WW 677...WW 678...



DISCUSSION...ONGOING SEVERE STORMS ALONG DIFFUSE OUTFLOW BOUNDARY

ACROSS CENTRAL LOWER MI WILL LIKELY PERSIST...WHILE ADDITIONAL

STORMS OVER LAKE MI MOVE ENEWD INTO SW LOWER MI BY 01Z.  RESIDUAL

STEEP LOW-LEVEL LAPSE RATES...MLCAPE NEAR 1000 J/KG...AND EFFECTIVE

BULK SHEAR AOA 40 KT WILL CONTINUE TO SUPPORT ORGANIZED CELLS/LINE

SEGMENTS CAPABLE OF PRODUCING LARGE HAIL AND DAMAGING WINDS.  THE

SEVERE THREAT SHOULD BEGIN TO DIMINISH TOWARD 04-05Z AS THE BOUNDARY

LAYER STABILIZES AND INSTABILITY WEAKENS.



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 25040.





...THOMPSON

