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140 

WWUS20 KWNS 121939

SEL7

SPC WW 121939

IDZ000-MTZ000-130300-



URGENT - IMMEDIATE BROADCAST REQUESTED

SEVERE THUNDERSTORM WATCH NUMBER 637

NWS STORM PREDICTION CENTER NORMAN OK

140 PM MDT TUE JUL 12 2011



THE NWS STORM PREDICTION CENTER HAS ISSUED A

SEVERE THUNDERSTORM WATCH FOR PORTIONS OF



       CENTRAL IDAHO

       WESTERN AND CENTRAL MONTANA



EFFECTIVE THIS TUESDAY AFTERNOON AND EVENING FROM 140 PM UNTIL

900 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 90

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

SOUTHWEST OF DILLON MONTANA TO 40 MILES NORTH NORTHWEST OF HAVRE

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.



OTHER WATCH INFORMATION...CONTINUE...WW 636...



DISCUSSION...THUNDERSTORMS ARE INCREASING FROM CENTRAL IDAHO INTO

SWRN MT...WITH ADDITIONAL STORMS CONTINUING TO MOVE NNEWD FROM NWRN

WY INTO SOUTH CENTRAL MT.  AIR MASS IS QUITE MOIST OVER THE AREA

WITH SURFACE DEW POINTS GENERALLY IN THE 50S...AND CONTINUED HEATING

DOWNSTREAM FORM THE STORMS WILL PROMOTE FURTHER DESTABILIZATION WITH

CAPE TO 1500 J/KG.  MODERATELY STRONG SWLY FLOW IN THE MID/UPPER

LEVELS WILL PROVIDE SUFFICIENT DEEP LAYER SHEAR TO ENHANCE STORM

ORGANIZATION AND INTENSITY.  STRONGER CELLS WILL BE CAPABLE OF

PRODUCING LARGE HAIL AND STRONG WIND GUSTS.



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.





...WEISS

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