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000 

WWUS20 KWNS 101847

SEL0

SPC WW 101847

MTZ000-NDZ000-SDZ000-WYZ000-110200-



URGENT - IMMEDIATE BROADCAST REQUESTED

SEVERE THUNDERSTORM WATCH NUMBER 820

NWS STORM PREDICTION CENTER NORMAN OK

1250 PM MDT SUN AUG 10 2008



THE NWS STORM PREDICTION CENTER HAS ISSUED A

SEVERE THUNDERSTORM WATCH FOR PORTIONS OF



       SOUTHEAST MONTANA

       SOUTHWEST NORTH DAKOTA

       WESTERN SOUTH DAKOTA

       NORTHEAST WYOMING



EFFECTIVE THIS SUNDAY AFTERNOON AND EVENING FROM 1250 PM UNTIL

800 PM MDT.



HAIL TO 2 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 65

STATUTE MILES EAST AND WEST OF A LINE FROM 30 MILES NORTHEAST OF

BAKER MONTANA TO 45 MILES SOUTHWEST OF RAPID CITY SOUTH DAKOTA.

FOR A COMPLETE DEPICTION OF THE WATCH SEE THE ASSOCIATED WATCH

OUTLINE UPDATE (WOUS64 KWNS WOU0).



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 817...WW 818...WW 819...



DISCUSSION...THUNDERSTORMS INCREASING INVOF SURFACE TROUGH NOW

EXTENDING FROM ERN MT INTO NERN WY...WHERE AIR MASS IS NOW

MODERATELY UNSTABLE AND UNCAPPED.  ACTIVITY IS BEING AIDING BY SLOW

MOVING SHORTWAVE TROUGH NOW MOVING ACROSS WY.  LARGE HAIL AND

ISOLATED DAMAGING WINDS WILL BE PRIMARY SEVERE THREATS...ALTHOUGH

SHEAR WILL REMAIN MARGINAL BUT STILL SUFFICIENT FOR BRIEF

SUPERCELLS.  ABUNDANT MOISTURE AND SLOW MOVING STORMS ALSO SUGGESTS

HEAVY RAINFALL WILL BE AN ADDITIONAL HAZARD.



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

TO 2 INCHES. EXTREME TURBULENCE AND SURFACE WIND GUSTS TO 60

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

MOTION VECTOR 27015.





...EVANS

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