

000 

WWUS20 KWNS 192334

SEL8

SPC WW 192334

MTZ000-WYZ000-200600-



URGENT - IMMEDIATE BROADCAST REQUESTED

SEVERE THUNDERSTORM WATCH NUMBER 618

NWS STORM PREDICTION CENTER NORMAN OK

530 PM MDT SUN AUG 19 2007



THE NWS STORM PREDICTION CENTER HAS ISSUED A

SEVERE THUNDERSTORM WATCH FOR PORTIONS OF



       SOUTHEAST MONTANA

       EASTERN WYOMING



EFFECTIVE THIS SUNDAY AFTERNOON FROM 530 PM UNTIL MIDNIGHT 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 95

STATUTE MILES EAST AND WEST OF A LINE FROM 25 MILES NORTH

NORTHWEST OF MILES CITY MONTANA TO 55 MILES SOUTH SOUTHWEST OF

DOUGLAS 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 617...



DISCUSSION...TSTMS...INCLUDING SOME SUSTAINED CELLS AND HIGHER-BASED

SUPERCELLS...HAVE FORMED OVER THE MOUNTAINS OF NRN/WRN WY AND SRN

MT.  THIS ACTIVITY IS IN ZONE OF INSTABILITY/UPLIFT ON SERN FRINGE

OF SHORTWAVE TROUGH ROTATING NE ACROSS THE NRN RCKYS.  BELT OF DEEP/

MODERATELY STRONG WLY FLOW OVERSPREADING WY WITH THE TROUGH SHOULD

MAINTAIN FAVORABLE ENVIRONMENT FOR SUSTAINED STORMS EWD INTO THE ERN

WY/SE MT PLNS.  GIVEN DEEPLY MIXED ENVIRONMENT PRESENT THERE...SOME

STORMS COULD YIELD HIGH WIND AND POSSIBLY HAIL THROUGH AT MID/LATE

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 26035.





...CORFIDI

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