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WWUS20 KWNS 131945

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URGENT - IMMEDIATE BROADCAST REQUESTED

SEVERE THUNDERSTORM WATCH NUMBER 639

NWS STORM PREDICTION CENTER NORMAN OK

145 PM MDT WED JUL 13 2011



THE NWS STORM PREDICTION CENTER HAS ISSUED A

SEVERE THUNDERSTORM WATCH FOR PORTIONS OF



       A SMALL PART OF CENTRAL IDAHO

       WESTERN MONTANA



EFFECTIVE THIS WEDNESDAY AFTERNOON AND EVENING FROM 145 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 85

STATUTE MILES EAST AND WEST OF A LINE FROM 20 MILES NORTH

NORTHEAST OF CUT BANK MONTANA TO 45 MILES SOUTH SOUTHWEST OF

SALMON IDAHO.  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 638...



DISCUSSION...STORMS ARE EXPECTED TO CONTINUE DEVELOPING OVER CENTRAL

IDAHO AND SOUTHWEST MONTANA AND MOVE NNEWD ALONG THE ERN EDGE OF A

STRONG SSWLY JET STREAM.  THE AIR MASS IS QUITE MOIST WITH SURFACE

DEW POINTS IN THE 50S CONTRIBUTING TO AN UNSTABLE ENVIRONMENT WITH

MLCAPE OF 1000-1500 J/KG. STRONGER CELLS WILL HAVE POTENTIAL TO

PRODUCE LARGE HAIL AND DAMAGING WIND GUSTS.



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 21035.





...WEISS

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