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WWUS20 KWNS 190023

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SPC WW 190023

MTZ000-NDZ000-SDZ000-WYZ000-190700-



URGENT - IMMEDIATE BROADCAST REQUESTED

SEVERE THUNDERSTORM WATCH NUMBER 492

NWS STORM PREDICTION CENTER NORMAN OK

620 PM MDT SUN JUL 18 2010



THE NWS STORM PREDICTION CENTER HAS ISSUED A

SEVERE THUNDERSTORM WATCH FOR PORTIONS OF



       SOUTHEASTERN MONTANA

       SOUTHWESTERN NORTH DAKOTA

       WESTERN SOUTH DAKOTA

       NORTHEASTERN WYOMING



EFFECTIVE THIS SUNDAY NIGHT AND MONDAY MORNING FROM 620 PM UNTIL

100 AM MDT.



HAIL TO 2 INCHES IN DIAMETER...THUNDERSTORM WIND GUSTS TO 80

MPH...AND DANGEROUS LIGHTNING ARE POSSIBLE IN THESE AREAS.



THE SEVERE THUNDERSTORM WATCH AREA IS APPROXIMATELY ALONG AND 90

STATUTE MILES EITHER SIDE OF A LINE FROM 15 MILES NORTH NORTHEAST

OF MILES CITY MONTANA TO 60 MILES NORTHEAST OF RAPID CITY SOUTH

DAKOTA.  FOR A COMPLETE DEPICTION OF THE WATCH SEE THE ASSOCIATED

WATCH OUTLINE UPDATE (WOUS64 KWNS WOU2).



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 491...



DISCUSSION...A COUPLE OF SUPERCELLS HAD DEVELOPED IN CENTRAL MT AND

ARE EXPECTED TO INCREASE IN COVERAGE THIS EVENING AS THE STORMS MOVE

SEWD ALONG MOIST AXIS AND INTO STRENGTHENING LOW LEVEL JET.

EFFECTIVE SHEAR AT 60 KT WILL RESULT IN STRONG ROTATION AND THE

LIKELIHOOD FOR LARGE HAIL. ALSO...STEEP LOW LEVEL LAPSE RATES ARE

FAVORABLE FOR SEVERE WINDS. AS THE LOW LEVEL JET INCREASES LATER

THIS EVENING...THE STORMS MAY EVOLVE INTO A LINEAR MCS...WHICH WOULD

THEN INCREASE THE GREATER POTENTIAL FOR WIND DAMAGE.



AVIATION...A FEW SEVERE THUNDERSTORMS WITH HAIL SURFACE AND ALOFT

TO 2 INCHES. EXTREME TURBULENCE AND SURFACE WIND GUSTS TO 70

KNOTS. A FEW CUMULONIMBI WITH MAXIMUM TOPS TO 500. MEAN STORM

MOTION VECTOR 31030.





...IMY

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