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URGENT - IMMEDIATE BROADCAST REQUESTED

SEVERE THUNDERSTORM WATCH NUMBER 650

NWS STORM PREDICTION CENTER NORMAN OK

235 PM MDT THU SEP 9 2010



THE NWS STORM PREDICTION CENTER HAS ISSUED A

SEVERE THUNDERSTORM WATCH FOR PORTIONS OF



       EXTREME EASTERN MONTANA

       WESTERN NORTH DAKOTA

       WESTERN SOUTH DAKOTA



EFFECTIVE THIS THURSDAY AFTERNOON AND EVENING FROM 235 PM UNTIL

1000 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 90

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

NORTHEAST OF WILLISTON NORTH DAKOTA TO 50 MILES SOUTHEAST 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.



DISCUSSION...THUNDERSTORMS ARE BEGINNING TO DEVELOP FROM SE MT INTO

WRN SD ALONG THE NOSE OF A DEEPLY MIXED BOUNDARY LAYER/STEEP

LOW-LEVEL LAPSE RATES.  AN INCREASE IN STORM COVERAGE/INTENSITY IS

EXPECTED THROUGH THE AFTERNOON/EVENING AS THE LOW LEVELS CONTINUE TO

DESTABILIZE S OF A WARM FRONT IN ND...AND AS A STRONG MIDLEVEL

TROUGH MOVES NEWD FROM WRN WY.  THERE WILL BE A SMALL WINDOW OF

OPPORTUNITY FOR AN ISOLATED TORNADO IN SW ND LATE THIS AFTERNOON AS

THE INITIAL CELLULAR STORMS INTERACT WITH THE SURFACE WARM FRONT.

HOWEVER...SOMEWHAT MARGINAL MOISTURE AND WEAKER LOW-LEVEL SHEAR

ACROSS WRN SD AND ERN MT...AS WELL AS A MORE STABLE BOUNDARY LAYER N

OF THE WARM FRONT IN ND...WILL SUPPORT LARGE HAIL AND DAMAGING WINDS

AS THE PRIMARY SEVERE THREATS.



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 450. MEAN STORM

MOTION VECTOR 24035.





...THOMPSON

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