

000 

WWUS20 KWNS 132032

SEL8

SPC WW 132032

MTZ000-140400-



URGENT - IMMEDIATE BROADCAST REQUESTED

SEVERE THUNDERSTORM WATCH NUMBER 268

NWS STORM PREDICTION CENTER NORMAN OK

230 PM MDT SUN MAY 13 2007



THE NWS STORM PREDICTION CENTER HAS ISSUED A

SEVERE THUNDERSTORM WATCH FOR PORTIONS OF



       SOUTHERN AND EASTERN MONTANA



EFFECTIVE THIS SUNDAY AFTERNOON AND EVENING FROM 230 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 75

STATUTE MILES NORTH AND SOUTH OF A LINE FROM 20 MILES NORTHWEST

OF LIVINGSTON MONTANA TO 10 MILES NORTHEAST OF BAKER MONTANA.

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.



DISCUSSION...STRONG SHORTWAVE TROUGH IS EXPECTED TO INCREASE

THUNDERSTORM COVERAGE AND INTENSITY FROM WEST TO EAST ACROSS WW LATE

TODAY AND THIS EVENING.  AIR MASS IS ALREADY MODERATELY UNSTABLE

WITH EFFECTIVE SHEAR FROM 40-50 KT PROVIDING AMPLE SHEAR FOR

SUPERCELLS AND ORGANIZED LINES.  LARGE HAIL AND DAMAGING WINDS ARE

EXPECTED AS STORMS SPREAD QUICKLY EWD ACROSS LOWER ELEVATIONS OF SRN

AND INTO ERN MT THIS EVENING.



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 27025.





...EVANS

