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601 

WWUS20 KWNS 062100

SEL8

SPC WW 062100

MTZ000-WYZ000-070400-



URGENT - IMMEDIATE BROADCAST REQUESTED

SEVERE THUNDERSTORM WATCH NUMBER 668

NWS STORM PREDICTION CENTER NORMAN OK

300 PM MDT THU AUG 6 2009



THE NWS STORM PREDICTION CENTER HAS ISSUED A

SEVERE THUNDERSTORM WATCH FOR PORTIONS OF



       SOUTH CENTRAL MONTANA

       NORTHWEST WYOMING



EFFECTIVE THIS THURSDAY AFTERNOON AND EVENING FROM 300 PM UNTIL

1000 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 60

STATUTE MILES EAST AND WEST OF A LINE FROM 55 MILES EAST

NORTHEAST OF HARLOWTON MONTANA TO 50 MILES EAST OF JACKSON

WYOMING.  FOR A COMPLETE DEPICTION OF THE WATCH SEE THE

ASSOCIATED WATCH OUTLINE UPDATE (WOUS64 KWNS WOU8).



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.



OTHER WATCH INFORMATION...CONTINUE...WW 666...WW 667...



DISCUSSION...STRONG SEVERE STORMS HAVE DEVELOPED IN A BAND FROM

EXTREME SERN ID NNEWD INTO SRN MT.  THIS ACTIVITY IS AHEAD OF A

STRONG UPPER LOW MOVING ENEWD INTO THE GREAT BASIN...AND INCREASING

DYNAMIC FORCING IS FORECAST TO SPREAD DOWNSTREAM TOWARD THE NRN

ROCKIES THIS EVENING.  LOW LEVEL MOISTURE WITH SURFACE DEW POINTS IN

THE UPPER 50S IS CONTRIBUTING TO MLCAPE OF 1000-1500 J/KG...AND

WSWLY MID LEVEL WINDS OF 40-45 KT ARE RESULTING IN DEEP LAYER SHEAR

SUPPORTIVE OF SEVERE STORMS INCLUDING ISOLATED SUPERCELLS.  LARGE

HAIL AND DAMAGING WINDS WILL BE POSSIBLE WITH STRONGER STORMS.



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 500. MEAN STORM

MOTION VECTOR 24030.





...WEISS

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