WATCHES: Severe Thunderstorm Watch Number 875

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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