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WWUS20 KWNS 311916

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SPC WW 311916

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URGENT - IMMEDIATE BROADCAST REQUESTED

TORNADO WATCH NUMBER 771

NWS STORM PREDICTION CENTER NORMAN OK

115 PM CST FRI DEC 31 2010



THE NWS STORM PREDICTION CENTER HAS ISSUED A

TORNADO WATCH FOR PORTIONS OF



       CENTRAL AND EASTERN ILLINOIS

       FAR NORTHWEST INDIANA



EFFECTIVE THIS FRIDAY AFTERNOON AND EVENING FROM 115 PM UNTIL 700

PM CST.



TORNADOES...HAIL TO 1 INCH IN DIAMETER...THUNDERSTORM WIND GUSTS

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



THE TORNADO WATCH AREA IS APPROXIMATELY ALONG AND 50 STATUTE

MILES EAST AND WEST OF A LINE FROM 45 MILES NORTH OF DANVILLE

ILLINOIS TO 5 MILES EAST SOUTHEAST OF SALEM ILLINOIS.  FOR A

COMPLETE DEPICTION OF THE WATCH SEE THE ASSOCIATED WATCH OUTLINE

UPDATE (WOUS64 KWNS WOU1).



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...THIS TORNADO WATCH REPLACES TORNADO

WATCH NUMBER 768. WATCH NUMBER 768 WILL NOT BE IN EFFECT AFTER

115 PM CST. CONTINUE...WW 767...WW 769...WW 770...



DISCUSSION...LOW-TOPPED TSTMS /SUPERCELLS/ ONGOING OVER CNTRL IL ARE

EXPECTED TO CONTINUE NEWD THIS AFTERNOON ALONG AND S OF WARM FRONT

RETREATING NWD THROUGH AREA.  THOUGH AMBIENT AIR MASS IS ONLY

MARGINALLY UNSTABLE...STRONG VERTICAL SHEAR AND FORCING FOR ASCENT

SHOULD SUSTAIN ONGOING STORMS WITH A RISK FOR DAMAGING WINDS AND A

COUPLE TORNADOES.



AVIATION...TORNADOES AND 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 350.

MEAN STORM MOTION VECTOR 22040.





...MEAD

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