

000 

WWUS20 KWNS 191939

SEL7

SPC WW 191939

IDZ000-MTZ000-WYZ000-200200-



URGENT - IMMEDIATE BROADCAST REQUESTED

SEVERE THUNDERSTORM WATCH NUMBER 617

NWS STORM PREDICTION CENTER NORMAN OK

135 PM MDT SUN AUG 19 2007



THE NWS STORM PREDICTION CENTER HAS ISSUED A

SEVERE THUNDERSTORM WATCH FOR PORTIONS OF



       SOUTHEAST IDAHO

       WESTERN AND CENTRAL MONTANA

       WESTERN AND CENTRAL WYOMING



EFFECTIVE THIS SUNDAY AFTERNOON AND EVENING FROM 135 PM UNTIL 800

PM MDT.



HAIL TO 2 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 100

STATUTE MILES EAST AND WEST OF A LINE FROM 15 MILES WEST OF BIG

PINEY WYOMING TO 85 MILES NORTHEAST OF GREAT FALLS MONTANA.  FOR

A COMPLETE DEPICTION OF THE WATCH SEE THE ASSOCIATED WATCH

OUTLINE UPDATE (WOUS64 KWNS WOU7).



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 FROM SERN ID INTO WRN

PARTS OF MT AND WY IN RESPONSE TO STRONG DYNAMIC FORCING ASSOCIATED

WITH VIGOROUS UPPER TROUGH MOVING EWD TOWARD THE NRN ROCKIES.

SUFFICIENT MOISTURE COUPLED WITH STEEP LAPSE RATES/STRONG HEATING IS

RESULTING IN UNSTABLE ENVIRONMENT WITH MLCAPE OF 1000-1500 J/KG.

STRONG MID/UPPER LEVEL JET STREAK MOVING ACROSS THE NRN

INTERMOUNTAIN REGION IS RESULTING IN 40-50 KT DEEP LAYER SHEAR

SUPPORTIVE OF SEVERE STORMS INCLUDING A FEW SUPERCELLS.  ACTIVITY

SHOULD SPREAD NEWD INTO THE EVENING HOURS.



AVIATION...A FEW SEVERE THUNDERSTORMS WITH HAIL SURFACE AND ALOFT

TO 2 INCHES. EXTREME TURBULENCE AND SURFACE WIND GUSTS TO 60

KNOTS. A FEW CUMULONIMBI WITH MAXIMUM TOPS TO 450. MEAN STORM

MOTION VECTOR 24035.





...WEISS

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