WATCHES: Severe Thunderstorm Watch Number 670

WWUS20 KWNS 161833
SEL0
SPC WW 161833
AZZ000-COZ000-UTZ000-170200-

URGENT - IMMEDIATE BROADCAST REQUESTED
SEVERE THUNDERSTORM WATCH NUMBER 670
NWS STORM PREDICTION CENTER NORMAN OK
1230 PM MDT SUN SEP 16 2007

THE NWS STORM PREDICTION CENTER HAS ISSUED A
SEVERE THUNDERSTORM WATCH FOR PORTIONS OF

NORTHERN ARIZONA
WESTERN COLORADO
EASTERN UTAH

EFFECTIVE THIS SUNDAY AFTERNOON AND EVENING FROM 1230 PM UNTIL
800 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 NORTHEAST OF
VERNAL UTAH TO 30 MILES SOUTH OF FLAGSTAFF ARIZONA. FOR A
COMPLETE DEPICTION OF THE WATCH SEE THE ASSOCIATED WATCH OUTLINE
UPDATE (WOUS64 KWNS WOU0).

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...DAYTIME HEATING WILL LIKELY LEAD TO SCATTERED
THUNDERSTORM DEVELOPMENT BY 19-20Z WITHIN A MOISTURE PLUME FROM NRN
AZ INTO ERN UT/WRN CO. MUCAPE VALUES ON THE ORDER OF 500-1500 J/KG
AND EFFECTIVE BULK SHEAR OF 35-50 KT /DOWNSTREAM FROM A MID LEVEL
TROUGH OVER CA/NV/ WILL PROVIDE A FAVORABLE ENVIRONMENT FOR STORMS
WITH SUPERCELL STRUCTURE...AND PERHAPS SHORT BOWING LINE SEGMENTS.
LARGE HAIL AND DAMAGING WINDS WILL BE THE PRIMARY THREATS 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 25030.

..THOMPSON

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