

000 

WWUS20 KWNS 211107

SEL8

SPC WW 211107

MIZ000-MNZ000-WIZ000-LSZ000-211700-



URGENT - IMMEDIATE BROADCAST REQUESTED

SEVERE THUNDERSTORM WATCH NUMBER 678

NWS STORM PREDICTION CENTER NORMAN OK

605 AM CDT FRI SEP 21 2007



THE NWS STORM PREDICTION CENTER HAS ISSUED A

SEVERE THUNDERSTORM WATCH FOR PORTIONS OF



       WESTERN UPPER PENINSULA OF MICHIGAN

       CENTRAL TO NORTHEASTERN MINNESOTA

       NORTHWESTERN AND NORTH-CENTRAL WISCONSIN

       LAKE SUPERIOR



EFFECTIVE THIS FRIDAY MORNING FROM 605 AM UNTIL NOON CDT.



HAIL TO 2.5 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 105

STATUTE MILES NORTH AND SOUTH OF A LINE FROM 25 MILES SOUTHWEST

OF BRAINERD MINNESOTA TO 45 MILES EAST NORTHEAST OF IRONWOOD

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...THIS SEVERE THUNDERSTORM WATCH REPLACES

TORNADO WATCH NUMBER 677. WATCH NUMBER 677 WILL NOT BE IN EFFECT

AFTER 605 AM CDT.



DISCUSSION...DEVELOPMENT OF TSTMS -- ROOTED ABOVE SFC IN LAYER OF

MOIST LLJ -- IS FCST TO CONTINUE THROUGH MIDMORNING HOURS IN

ENVIRONMENT OF FAVORABLE ELEVATED MUCAPES UP TO ABOUT 2000 J/KG AND

EFFECTIVE BULK SHEARS UP TO ABOUT 40 KT.  MAIN THREAT WILL BE

INTERMITTENT LARGE HAIL.



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

TO 2.5 INCHES. EXTREME TURBULENCE AND SURFACE WIND GUSTS TO 60

KNOTS. A FEW CUMULONIMBI WITH MAXIMUM TOPS TO 450. MEAN STORM

MOTION VECTOR 24035.





...EDWARDS/HART

