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WWUS20 KWNS 121954

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URGENT - IMMEDIATE BROADCAST REQUESTED

TORNADO WATCH NUMBER 468

NWS STORM PREDICTION CENTER NORMAN OK

150 PM MDT SUN JUN 12 2011



THE NWS STORM PREDICTION CENTER HAS ISSUED A

TORNADO WATCH FOR PORTIONS OF



       SOUTHEAST MONTANA

       SOUTHWEST NORTH DAKOTA

       WESTERN SOUTH DAKOTA

       NORTHEAST WYOMING



EFFECTIVE THIS SUNDAY AFTERNOON AND EVENING FROM 150 PM UNTIL 800

PM MDT.



TORNADOES...HAIL TO 2.5 INCHES IN DIAMETER...THUNDERSTORM WIND

GUSTS TO 70 MPH...AND DANGEROUS LIGHTNING ARE POSSIBLE IN THESE

AREAS.



THE TORNADO WATCH AREA IS APPROXIMATELY ALONG AND 90 STATUTE

MILES EAST AND WEST OF A LINE FROM 35 MILES EAST NORTHEAST OF

BAKER MONTANA TO 70 MILES SOUTH OF RAPID CITY SOUTH DAKOTA.  FOR

A COMPLETE DEPICTION OF THE WATCH SEE THE ASSOCIATED WATCH

OUTLINE UPDATE (WOUS64 KWNS WOU8).



REMEMBER...A TORNADO WATCH MEANS CONDITIONS ARE FAVORABLE FOR

TORNADOES AND 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.



OTHER WATCH INFORMATION...CONTINUE...WW 467...



DISCUSSION...SURFACE HEATING IS REMOVING CONVECTIVE INHIBITION

ACROSS NE WY/SW SD NEAR THE SURFACE LOW AND WARM FRONT...WITH STORM

DEVELOPMENT EXPECTED BY 21-22Z.  STORM DEVELOPMENT WILL BE FURTHER

SUPPORTED BY THE APPROACH OF THE PRIMARY SHORTWAVE TROUGH OVER NW

WY/S CENTRAL MT...AND A SEPARATE SPEED MAX EJECTING NEWD FROM NRN

CO.  MODERATE INSTABILITY IS PRESENT IN THE WARM SECTOR /MLCAPE AOA

2000 J PER KG/...WHILE VERTICAL SHEAR IS FAVORABLE FOR SUPERCELLS

WITH LARGE HAIL.  THE MORE PROBABLE AREA FOR A COUPLE OF TORNADOES

WILL BE NE WY/NW SD WHERE LOW-LEVEL SHEAR AND MOISTURE ARE MAXIMIZED

ALONG THE WARM FRONT...AND WHERE INITIALLY DISCRETE STORMS ARE

EXPECTED.  LATER THIS AFTERNOON/EVENING...CONVECTION WILL LIKELY

GROW UPSCALE INTO A CLUSTER/MCS AND SPREAD NEWD WITH A CONTINUED

RISK FOR LARGE HAIL AND DAMAGING WINDS.



AVIATION...TORNADOES AND A FEW SEVERE THUNDERSTORMS WITH HAIL

SURFACE AND ALOFT TO 2.5 INCHES. EXTREME TURBULENCE AND SURFACE

WIND GUSTS TO 60 KNOTS. A FEW CUMULONIMBI WITH MAXIMUM TOPS TO

500. MEAN STORM MOTION VECTOR 23025.





...THOMPSON

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