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000 

WWUS20 KWNS 311921

SEL5

SPC WW 311921

IDZ000-UTZ000-WYZ000-010300-



URGENT - IMMEDIATE BROADCAST REQUESTED

SEVERE THUNDERSTORM WATCH NUMBER 875

NWS STORM PREDICTION CENTER NORMAN OK

120 PM MDT SUN AUG 31 2008



THE NWS STORM PREDICTION CENTER HAS ISSUED A

SEVERE THUNDERSTORM WATCH FOR PORTIONS OF



       SOUTHEAST IDAHO

       WESTERN AND NORTHERN UTAH

       EXTREME SOUTHWEST WYOMING



EFFECTIVE THIS SUNDAY AFTERNOON AND EVENING FROM 120 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 35 MILES NORTHEAST OF

POCATELLO IDAHO TO 55 MILES SOUTH SOUTHWEST OF DELTA UTAH.  FOR A

COMPLETE DEPICTION OF THE WATCH SEE THE ASSOCIATED WATCH OUTLINE

UPDATE (WOUS64 KWNS WOU5).



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.



DISCUSSION...THUNDERSTORMS ARE INCREASING GRADUALLY IN

COVERAGE/INTENSITY ALONG A COLD FRONT MOVING EWD ACROSS NE NV.  THE

COLD FRONT COINCIDES WITH A DEEPER BAND OF ASCENT DOWNSTREAM FROM A

MID LEVEL SHORTWAVE TROUGH EJECTING EWD OVER NW NV.  EXPECT THE

CONVECTION TO SPREAD EWD THIS AFTERNOON INTO W/NW UT AND SE ID AS

THE COLD FRONT ENCOUNTERS A SOMEWHAT MORE MOIST ENVIRONMENT ON THE

WRN FRINGES OF A MONSOONAL MOISTURE PLUME ACROSS UT.  STRENGTHENING

UNIDIRECTIONAL WIND PROFILES AND MODEST INSTABILITY WILL SUPPORT A

LINE OF STORMS ALONG AND E OF THE FRONT...WITH SOME EMBEDDING

BOW/SUPERCELL STRUCTURES POSSIBLE.  DAMAGING WINDS CAN BE EXPECTED

WITH THE STRONGEST STORMS...AS WELL AS ISOLATED LARGE HAIL.



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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