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462 

WWUS20 KWNS 231853

SEL3

SPC WW 231853

MTZ000-240200-



URGENT - IMMEDIATE BROADCAST REQUESTED

SEVERE THUNDERSTORM WATCH NUMBER 543

NWS STORM PREDICTION CENTER NORMAN OK

1255 PM MDT THU JUN 23 2011



THE NWS STORM PREDICTION CENTER HAS ISSUED A

SEVERE THUNDERSTORM WATCH FOR PORTIONS OF



       LARGE PART OF WESTERN MONTANA



EFFECTIVE THIS THURSDAY AFTERNOON AND EVENING FROM 1255 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 135

STATUTE MILES EAST AND WEST OF A LINE FROM 50 MILES EAST

NORTHEAST OF CUT BANK MONTANA TO 40 MILES SOUTH SOUTHEAST OF

HELENA MONTANA.  FOR A COMPLETE DEPICTION OF THE WATCH SEE THE

ASSOCIATED WATCH OUTLINE UPDATE (WOUS64 KWNS WOU3).



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 541...WW 542...



DISCUSSION...THUNDERSTORMS ARE DEVELOPING OVER THE HIGHER TERRAIN

AHEAD OF THE COLD FRONT AND APPROACHING UPPER TROUGH.  WITH MLCAPES

AOA 1000 J/KG... VERY STEEP LAPSE RATES AND 40-50KT OF DEEP LAYER

SHEAR...DAMAGING WINDS WILL DEVELOP WITH THE STORMS AS THEY FORM

CLUSTERS AND BOWING SEGMENTS.  IN ADDITION LARGE HAIL IS LIKELY

GIVEN THE STEEP LAPSE RATES AND SHEAR PROFILES.



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 24035.





...HALES

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