Wednesday, June 20, 2007

WATCHES: Severe Thunderstorm Watch Number 429

WWUS20 KWNS 202025
SEL9
SPC WW 202025
IDZ000-MTZ000-210300-

URGENT - IMMEDIATE BROADCAST REQUESTED
SEVERE THUNDERSTORM WATCH NUMBER 429
NWS STORM PREDICTION CENTER NORMAN OK
225 PM MDT WED JUN 20 2007

THE NWS STORM PREDICTION CENTER HAS ISSUED A
SEVERE THUNDERSTORM WATCH FOR PORTIONS OF

CENTRAL IDAHO
WESTERN MONTANA

EFFECTIVE THIS WEDNESDAY AFTERNOON AND EVENING FROM 225 PM UNTIL
900 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 110
STATUTE MILES EAST AND WEST OF A LINE FROM 80 MILES NORTH
NORTHEAST OF MISSOULA MONTANA TO 30 MILES EAST SOUTHEAST OF
DILLON MONTANA. 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.

OTHER WATCH INFORMATION...CONTINUE...WW 428...

DISCUSSION...STORMS ARE EXPECTED TO INCREASE IN INTENSITY AND
COVERAGE INTO THE EVENING HOURS...AS AN UPPER LEVEL IMPULSE IN NRN
NV APPROACHES THE REGION. STEEP MID LEVEL LAPSE RATES AND 40-50 KT
DEEP LAYER SHEAR WILL BE SUFFICIENT FOR SUPERCELLS. ALTHOUGH SOME
HAIL IS EXPECTED... THE WELL MIXED AND DEEP BOUNDARY LAYER INDICATES
THAT WIND DAMAGE SHOULD BE THE MAIN THREAT.

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 23030.


..IMY

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