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WWUS20 KWNS 011943

SEL6

SPC WW 011943

IDZ000-MTZ000-020400-



URGENT - IMMEDIATE BROADCAST REQUESTED

SEVERE THUNDERSTORM WATCH NUMBER 436

NWS STORM PREDICTION CENTER NORMAN OK

140 PM MDT THU JUL 1 2010



THE NWS STORM PREDICTION CENTER HAS ISSUED A

SEVERE THUNDERSTORM WATCH FOR PORTIONS OF



       A SMALL PART OF EAST CENTRAL IDAHO

       SOUTHWEST...CENTRAL...AND  NORTHEAST MONTANA



EFFECTIVE THIS THURSDAY AFTERNOON AND EVENING FROM 140 PM UNTIL

1000 PM MDT.



HAIL TO 2.5 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 135

STATUTE MILES EAST AND WEST OF A LINE FROM 50 MILES EAST

SOUTHEAST OF DILLON MONTANA TO 55 MILES NORTH NORTHEAST OF

GLASGOW MONTANA.  FOR A COMPLETE DEPICTION OF THE WATCH SEE THE

ASSOCIATED WATCH OUTLINE UPDATE (WOUS64 KWNS WOU6).



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 435...



DISCUSSION...LIKE PREVIOUS DAYS...THUNDERSTORMS ARE BEGINNING TO

DEVELOP OVER THE HIGH TERRAIN NEAR AND NE OF THE ID/SW MT BORDER.

CONTINUED SURFACE HEATING ACROSS CENTRAL MT WILL CONTRIBUTE TO

ADDITIONAL DESTABILIZATION IN AN ENVIRONMENT WITH BOUNDARY LAYER

DEWPOINTS IN THE LOW-MID 50S.  THIS AREA IS ALSO DOWNSTREAM FROM A

MIDLEVEL TROUGH OVER THE PAC NW...WITH A SUBTLE/EMBEDDED VORTICITY

LOBE EJECTING NEWD OVER WRN MT.  THE COMBINATION OF WEAK BACKGROUND

ASCENT AND DEEP-LAYER VERTICAL SHEAR WITH THIS EJECTING WAVE WILL

SUPPORT A FEW SUPERCELLS CAPABLE OF PRODUCING ISOLATED VERY LARGE

HAIL AND DAMAGING WINDS.  AN ISOLATED TORNADO CANNOT BE RULED

OUT...THOUGH LOW-LEVEL MOISTURE/SHEAR ARE MARGINAL FOR A TORNADO

THREAT.  OTHERWISE...CONVECTION MAY MERGE INTO LARGER CLUSTERS

DURING THE EVENING AND SPREAD NEWD INTO NE MT WITH A CONTINUED

DAMAGING WIND/HAIL THREAT.



AVIATION...A FEW SEVERE THUNDERSTORMS WITH HAIL SURFACE AND ALOFT

TO 2.5 INCHES. EXTREME TURBULENCE AND SURFACE WIND GUSTS TO 60

KNOTS. A FEW CUMULONIMBI WITH MAXIMUM TOPS TO 500. MEAN STORM

MOTION VECTOR 25030.





...THOMPSON

