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000 

WWUS20 KWNS 220121

SEL2

SPC WW 220121

MIZ000-LHZ000-LMZ000-LSZ000-220800-



URGENT - IMMEDIATE BROADCAST REQUESTED

SEVERE THUNDERSTORM WATCH NUMBER 682

NWS STORM PREDICTION CENTER NORMAN OK

920 PM EDT FRI SEP 21 2007



THE NWS STORM PREDICTION CENTER HAS ISSUED A

SEVERE THUNDERSTORM WATCH FOR PORTIONS OF



       EASTERN UPPER AND NORTHERN LOWER MICHIGAN

       LAKE HURON

       LAKE MICHIGAN

       LAKE SUPERIOR



EFFECTIVE THIS FRIDAY NIGHT AND SATURDAY MORNING FROM 920 PM

UNTIL 400 AM EDT.



HAIL TO 0.5 INCH 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 90

STATUTE MILES EAST AND WEST OF A LINE FROM 55 MILES SOUTH

SOUTHWEST OF PELLSTON MICHIGAN TO 50 MILES WEST NORTHWEST OF

SAULT STE MARIE 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.



OTHER WATCH INFORMATION...CONTINUE...WW 679...WW 681...



DISCUSSION...STRONG UPR MS VLY SHORTWAVE TROUGH APPEARS TO BE

ASSUMING A NEGATIVE TILT PER SATELLITE AND SFC PRESSURE CHANGE DATA.

THIS MAY ENHANCE POTENTIAL FOR STRENGTHENING OF EXISTING CONVECTION

INTO ONE OR TWO BANDS OF LOW-TOPPED STORMS THAT COULD YIELD HIGH

WIND...GIVEN 40-50 KT LOW TO MID LVL WIND FIELD AND WEAK

INSTABILITY.



AVIATION...A FEW SEVERE THUNDERSTORMS WITH HAIL SURFACE AND ALOFT

TO 0.5 INCH. EXTREME TURBULENCE AND SURFACE WIND GUSTS TO 60

KNOTS. A FEW CUMULONIMBI WITH MAXIMUM TOPS TO 400. MEAN STORM

MOTION VECTOR 23045.





...CORFIDI

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