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000 

WWUS20 KWNS 052302

SEL1

SPC WW 052302

MTZ000-SDZ000-WYZ000-060500-



URGENT - IMMEDIATE BROADCAST REQUESTED

SEVERE THUNDERSTORM WATCH NUMBER 811

NWS STORM PREDICTION CENTER NORMAN OK

500 PM MDT TUE AUG 5 2008



THE NWS STORM PREDICTION CENTER HAS ISSUED A

SEVERE THUNDERSTORM WATCH FOR PORTIONS OF



       SOUTHEASTERN MONTANA

       WESTERN SOUTH DAKOTA

       NORTHEASTERN WYOMING



EFFECTIVE THIS TUESDAY AFTERNOON AND EVENING FROM 500 PM UNTIL

1100 PM MDT.



HAIL TO 3 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 75

STATUTE MILES EAST AND WEST OF A LINE FROM 10 MILES EAST

NORTHEAST OF MILES CITY MONTANA TO 80 MILES SOUTH SOUTHWEST OF

RAPID CITY SOUTH DAKOTA.  FOR A COMPLETE DEPICTION OF THE WATCH

SEE THE ASSOCIATED WATCH OUTLINE UPDATE (WOUS64 KWNS WOU1).



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 810...



DISCUSSION...COMBINATION OF SHORTWAVE TROUGH MOVING INTO CENTRAL MT

AND UPSLOPE FLOW HAVE CONTRIBUTED TO THUNDERSTORMS TO RECENTLY

DEVELOP OVER SERN MT. THESE STORMS ARE EXPECTED TO TRACK SEWD ALONG

A WEAK BOUNDARY THAT EXTENDED FROM SERN MT TO NEAR RAPID CITY...SD.

MODERATE INSTABILITY AND EFFECTIVE SHEAR AT 50 KT WILL BE FAVORABLE

FOR SUPERCELLS...WITH LARGE HAIL AND SOME WIND DAMAGE LIKELY THROUGH

THE EVENING HOURS.



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

TO 3 INCHES. EXTREME TURBULENCE AND SURFACE WIND GUSTS TO 60

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

MOTION VECTOR 32020.





...IMY

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