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050 

WWUS20 KWNS 072040

SEL2

SPC WW 072040

MTZ000-WYZ000-080400-



URGENT - IMMEDIATE BROADCAST REQUESTED

SEVERE THUNDERSTORM WATCH NUMBER 672

NWS STORM PREDICTION CENTER NORMAN OK

240 PM MDT FRI AUG 7 2009



THE NWS STORM PREDICTION CENTER HAS ISSUED A

SEVERE THUNDERSTORM WATCH FOR PORTIONS OF



       SOUTHERN MONTANA

       NORTHERN WYOMING



EFFECTIVE THIS FRIDAY AFTERNOON AND EVENING FROM 240 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 80

STATUTE MILES NORTH AND SOUTH OF A LINE FROM 45 MILES SOUTHWEST

OF BILLINGS MONTANA TO 70 MILES EAST SOUTHEAST OF BROADUS

MONTANA.  FOR A COMPLETE DEPICTION OF THE WATCH SEE THE

ASSOCIATED WATCH OUTLINE UPDATE (WOUS64 KWNS WOU2).



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...STORMS ARE EXPECTED TO INTENSIFY ACROSS SRN MT/NRN WY

AS THEY CONTINUE DEVELOPING ALONG A WEAK COLD FRONT IN NRN WY AND

OTHER BOUNDARIES IN SRN MT. ALTHOUGH SURFACE WINDS ARE FROM THE

NORTH ACROSS THE REGION...DEEP SLY/SWLY WINDS ALOFT WERE RESULTING

IN 40-50 KT OF DEEP LAYER SHEAR. THIS SHEAR COMBINED WITH THE MOIST

AND MODERATELY UNSTABLE AIR MASS WILL BE FAVORABLE FOR SUPERCELLS.

THE THERMODYNAMIC ENVIRONMENT APPEARS MOST FAVORABLE FOR LARGE HAIL

...THOUGH THE STRONG DOWNDRAFTS MAY ALSO RESULT IN SPORADIC WIND

DAMAGE.



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 23025.





...IMY

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