SPC Severe Thunderstorm Watch 666

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