WATCHES: Severe Thunderstorm Watch Number 431

WWUS20 KWNS 301959
SEL1
SPC WW 301959
IDZ000-MTZ000-010300-

URGENT - IMMEDIATE BROADCAST REQUESTED
SEVERE THUNDERSTORM WATCH NUMBER 431
NWS STORM PREDICTION CENTER NORMAN OK
200 PM MDT WED JUN 30 2010

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

PARTS OF CENTRAL AND EASTERN IDAHO
SOUTHWEST AND CENTRAL MONTANA

EFFECTIVE THIS WEDNESDAY AFTERNOON AND EVENING FROM 200 PM UNTIL
900 PM MDT.

HAIL TO 1.5 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 75
STATUTE MILES EAST AND WEST OF A LINE FROM 40 MILES NORTHWEST OF
LEWISTOWN MONTANA TO 95 MILES SOUTHWEST OF MONIDA MONTANA. FOR A
COMPLETE DEPICTION OF THE WATCH SEE THE ASSOCIATED WATCH OUTLINE
UPDATE (WOUS64 KWNS WOU1).

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 430...

DISCUSSION...THUNDERSTORMS ARE BEGINNING TO DEVELOP OVER THE HIGHER
TERRAIN OF SW MT AND ID...ALONG A BAROCLINIC ZONE AND BAND OF
MODERATE SWLY FLOW ALOFT. SURFACE HEATING IN THE WAKE OF EARLIER
CONVECTION HAS RESULTED IN SUBSTANTIAL DESTABILIZATION...WITH MLCAPE
NOW NEAR 1500 J/KG. THIS INSTABILITY...COMBINED WITH STRAIGHT
HODOGRAPHS AND EFFECTIVE BULK SHEAR NEAR 50 KT...WILL SUPPORT A FEW
SUPERCELLS AND/OR SMALL BOWING SEGMENTS CAPABLE OF PRODUCING
DAMAGING WINDS AND LARGE HAIL THROUGH THIS EVENING.

AVIATION...A FEW SEVERE THUNDERSTORMS WITH HAIL SURFACE AND ALOFT
TO 1.5 INCHES. EXTREME TURBULENCE AND SURFACE WIND GUSTS TO 60
KNOTS. A FEW CUMULONIMBI WITH MAXIMUM TOPS TO 450. MEAN STORM
MOTION VECTOR 24030.

...THOMPSON

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