WW 666 SEVERE TSTM IL MO 171900Z – 180100Z
URGENT - IMMEDIATE BROADCAST REQUESTED SEVERE THUNDERSTORM WATCH NUMBER 666 NWS STORM PREDICTION CENTER NORMAN OK 200 PM CDT WED OCT 17 2012 THE NWS STORM PREDICTION CENTER HAS ISSUED A SEVERE THUNDERSTORM WATCH FOR PORTIONS OF A SMALL PART OF SOUTHWEST ILLINOIS PARTS OF SOUTHERN AND EASTERN MISSOURI EFFECTIVE THIS WEDNESDAY AFTERNOON AND EVENING FROM 200 PM UNTIL 800 PM CDT. HAIL TO 1 INCH 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 70 STATUTE MILES EAST AND WEST OF A LINE FROM 40 MILES NORTHWEST OF SAINT LOUIS MISSOURI TO 40 MILES WEST SOUTHWEST OF WEST PLAINS MISSOURI. FOR A COMPLETE DEPICTION OF THE WATCH SEE THE ASSOCIATED WATCH OUTLINE UPDATE (WOUS64 KWNS WOU6). 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...A SQUALL LINE IS BEGINNING TO FORM IN THE ZONE OF ASCENT IMMEDIATELY PRECEDING THE SURFACE COLD FRONT AND AN ASSOCIATED STRONG MIDLEVEL TROUGH APPROACHING MO FROM ERN KS. THOUGH CLOUDS HAVE LIMITED SURFACE HEATING ACROSS MO TODAY...CONTINUED LOW-LEVEL MOISTENING WILL CONTRIBUTE TO AT LEAST WEAK SURFACE-BASED INSTABILITY THIS AFTERNOON ACROSS SRN AND ERN MO. GIVEN THE STRONGLY FORCED LINE AND 40-50 KT LOW-MIDLEVEL FLOW...THERE WILL BE A RISK FOR DAMAGING GUSTS WITH EMBEDDED BOWING SEGMENTS. AVIATION...A FEW SEVERE THUNDERSTORMS WITH HAIL SURFACE AND ALOFT TO 1 INCH. EXTREME TURBULENCE AND SURFACE WIND GUSTS TO 60 KNOTS. A FEW CUMULONIMBI WITH MAXIMUM TOPS TO 400. MEAN STORM MOTION VECTOR 25040. ...THOMPSON
via SPC Forecast Products http://www.spc.noaa.gov/products/watch/ww0666.html
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