URGENT - IMMEDIATE BROADCAST REQUESTED SEVERE THUNDERSTORM WATCH NUMBER 470 NWS STORM PREDICTION CENTER NORMAN OK 105 AM CDT THU AUG 21 2014 THE NWS STORM PREDICTION CENTER HAS ISSUED A SEVERE THUNDERSTORM WATCH FOR PORTIONS OF SOUTHERN MINNESOTA EFFECTIVE THIS THURSDAY MORNING FROM 105 AM UNTIL 700 AM CDT. PRIMARY THREATS INCLUDE... ISOLATED LARGE HAIL EVENTS TO 1.5 INCHES IN DIAMETER POSSIBLE THE SEVERE THUNDERSTORM WATCH AREA IS APPROXIMATELY ALONG AND 60 STATUTE MILES NORTH AND SOUTH OF A LINE FROM 60 MILES SOUTHWEST OF ALEXANDRIA MINNESOTA TO 35 MILES NORTH NORTHEAST OF MANKATO MINNESOTA. FOR A COMPLETE DEPICTION OF THE WATCH SEE THE ASSOCIATED WATCH OUTLINE UPDATE (WOUS64 KWNS WOU0). PRECAUTIONARY/PREPAREDNESS ACTIONS... 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...THUNDERSTORM DEVELOPMENT WAS UNDERWAY ACROSS WRN MN LATE TONIGHT AHEAD OF A SHORTWAVE TROUGH AND ASSOCIATED SURFACE LOW AND WARM FRONT SITUATED ACROSS THE NRN PLAINS. LIFT OCCURRING ACROSS THE WARM FRONT SHOULD CONTINUE TO AID UPDRAFT DEVELOPMENT ON THE EDGE OF STRONGER CAPPING INVERSION. MODEST INSTABILITY AND INCREASING SHEAR SHOULD CONTRIBUTE TO HAIL PRODUCTION FROM SOME OF THE STRONGER CELLS. DOWNWARD MOMENTUM TRANSFER MAY ALSO RESULT IN GUSTY/STRONGER WINDS GIVEN RELATIVELY WEAK BOUNDARY LAYER INHIBITION. EXPECT THIS CONVECTION TO SPREAD EAST ACROSS PARTS OF SRN MN OVER THE NEXT SEVERAL HOURS SUSTAINED BY THE SHORTWAVE TROUGH AND ENHANCED MASS TRANSPORT ON THE NOSE OF 40KT LOW LEVEL JET. AVIATION...A FEW SEVERE THUNDERSTORMS WITH HAIL SURFACE AND ALOFT TO 1.5 INCHES. EXTREME TURBULENCE AND SURFACE WIND GUSTS TO 50 KNOTS. A FEW CUMULONIMBI WITH MAXIMUM TOPS TO 550. MEAN STORM MOTION VECTOR 27025.
Posted on: Thu, 21 Aug 2014 11:24:14 +0000
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