

000 

WWUS20 KWNS 220458

SEL6

SPC WW 220458

WIZ000-220800-



URGENT - IMMEDIATE BROADCAST REQUESTED

SEVERE THUNDERSTORM WATCH NUMBER 636

NWS STORM PREDICTION CENTER NORMAN OK

1155 PM CDT TUE AUG 21 2007



THE NWS STORM PREDICTION CENTER HAS ISSUED A

SEVERE THUNDERSTORM WATCH FOR PORTIONS OF



       SOUTHERN WISCONSIN



EFFECTIVE THIS TUESDAY NIGHT AND WEDNESDAY MORNING FROM 1155 PM

UNTIL 300 AM CDT.



HAIL TO 1 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 40

STATUTE MILES EAST AND WEST OF A LINE FROM 45 MILES NORTH OF

MADISON WISCONSIN TO 40 MILES WEST OF JANESVILLE WISCONSIN.  FOR

A COMPLETE DEPICTION OF THE WATCH SEE THE ASSOCIATED WATCH

OUTLINE UPDATE (WOUS64 KWNS WOU6).



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 634...WW 635...



DISCUSSION...SMALL COMMA-SHAPED CONVECTIVE SYSTEM NOW ENTERING SW WI

EXPECTED TO CONTINUE ENE AT 40 + KTS.  BOUNDARY LAYER THAT SYSTEM

WILL ENCOUNTER IN SRN WI BECOMES INCREASINGLY HOSTILE TO SFC-BASED

UPDRAFT DEVELOPMENT WITH EWD EXTENT.  HOWEVER...MODERATE WSWLY SHEAR

ON SRN FRINGE OF MN MID LVL SPEED MAX...COUPLED WITH VERY

MOIST/SLIGHTLY-BACKED NEAR-SFC FLOW...SUGGESTS THAT SYSTEM MAY

CONTINUE POSE A RISK FOR DAMAGING WIND INTO S CNTRL WI.  INCREASING

CIN SHOULD PROHIBIT FURTHER SWD DEVELOPMENT OF CONVECTIVE BAND.

DEEP UNIDIRECTIONAL WSWLY WIND PROFILES IN NRN IA WILL SUPPORT A

PROLONGED PERIOD OF BACK-BUILDING/TRAINING IN WAKE OF SYSTEM...WITH

THE LIKELIHOOD FOR EXCESSIVE RAIN.



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

TO 1 INCH. EXTREME TURBULENCE AND SURFACE WIND GUSTS TO 60 KNOTS.

A FEW CUMULONIMBI WITH MAXIMUM TOPS TO 500. MEAN STORM MOTION

VECTOR 26045.





...CORFIDI

