

571 

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

