Friday, August 7, 2009

WATCHES: Severe Thunderstorm Watch Number 672

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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