

000 

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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