

911 

WWUS20 KWNS 112250

SEL9

SPC WW 112250

MTZ000-NDZ000-120600-



URGENT - IMMEDIATE BROADCAST REQUESTED

SEVERE THUNDERSTORM WATCH NUMBER 599

NWS STORM PREDICTION CENTER NORMAN OK

450 PM MDT WED AUG 11 2010



THE NWS STORM PREDICTION CENTER HAS ISSUED A

SEVERE THUNDERSTORM WATCH FOR PORTIONS OF



       NORTH CENTRAL AND NORTHEAST MONTANA

       NORTHWEST NORTH DAKOTA



EFFECTIVE THIS WEDNESDAY AFTERNOON FROM 450 PM UNTIL MIDNIGHT MDT.



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 65

STATUTE MILES NORTH AND SOUTH OF A LINE FROM 40 MILES SOUTH

SOUTHWEST OF HAVRE MONTANA TO 30 MILES EAST SOUTHEAST OF MINOT

NORTH DAKOTA.  FOR A COMPLETE DEPICTION OF THE WATCH SEE THE

ASSOCIATED WATCH OUTLINE UPDATE (WOUS64 KWNS WOU9).



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...STRONG/SEVERE THUNDERSTORMS HAVE DEVELOPED RECENTLY IN

CENTRAL MT AND SHOULD EXPAND IN COVERAGE/INTENSITY THROUGH THE

EVENING ACROSS NE MT AND NW ND...IN ADVANCE OF AN EJECTING MIDLEVEL

TROUGH OVER THE NRN ROCKIES.  THE STORMS WILL MOVE EWD ALONG A

STALLED FRONT WITH MODEST BOUNDARY LAYER MOISTURE AND STEEP LAPSE

RATES CONTRIBUTING TO MLCAPE NEAR 2000 J/KG ON THE COOL SIDE OF THE

BOUNDARY...WHERE VERTICAL SHEAR IS SUFFICIENT FOR SUPERCELLS.  LARGE

HAIL SHOULD BE THE MAIN THREAT INITIALLY IN MT...WHILE THE DAMAGING

WIND THREAT SHOULD INCREASE LATER THIS EVENING/TONIGHT AS STORM

MERGERS/INTERACTIONS PROMOTE UPSCALE GROWTH INTO A CLUSTER OR TWO.



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 500. MEAN STORM

MOTION VECTOR 27020.





...THOMPSON

