

125 

WWUS20 KWNS 312047

SEL8

SPC WW 312047

ILZ000-INZ000-010300-



URGENT - IMMEDIATE BROADCAST REQUESTED

SEVERE THUNDERSTORM WATCH NUMBER 508

NWS STORM PREDICTION CENTER NORMAN OK

345 PM CDT SAT AUG 31 2013



THE NWS STORM PREDICTION CENTER HAS ISSUED A



* SEVERE THUNDERSTORM WATCH FOR PORTIONS OF

  PARTS OF CENTRAL AND SOUTHERN ILLINOIS

  WEST CENTRAL AND SOUTHWESTERN INDIANA



* EFFECTIVE THIS SATURDAY AFTERNOON AND EVENING FROM 345 PM UNTIL

  1000 PM CDT.



* PRIMARY THREATS INCLUDE...

  SEVERAL LARGE HAIL EVENTS WITH A FEW VERY LARGE HAIL EVENTS TO 2

    INCHES IN DIAMETER POSSIBLE

  SEVERAL DAMAGING WIND GUSTS TO 70 MPH POSSIBLE



THE SEVERE THUNDERSTORM WATCH AREA IS APPROXIMATELY ALONG AND 70

STATUTE MILES EITHER SIDE OF A LINE FROM 10 MILES NORTH OF

SPRINGFIELD ILLINOIS TO 5 MILES SOUTHEAST OF BLOOMINGTON INDIANA.

 FOR A COMPLETE DEPICTION OF THE WATCH SEE THE ASSOCIATED WATCH

OUTLINE UPDATE (WOUS64 KWNS WOU8).



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.



&&



OTHER WATCH INFORMATION...CONTINUE...WW 507...



DISCUSSION...THUNDERSTORMS HAVE BEGUN INCREASING NEAR A WEAK SURFACE

LOW OVER NORTH CENTRAL ILLINOIS AND EAST-SOUTHEASTWARD ALONG A WEAK

WARM FRONT.  CU FIELD IS ALSO INCREASING SOUTHWESTWARD FROM THE LOW

ALONG A WEAK COOL FRONT -- ALL WITHIN A VERY MOIST ENVIRONMENT WHERE

DAYTIME HEATING HAS YIELDED 2500 TO 3000 J/KG MIXED-LAYER CAPE.

SHEAR IS SUFFICIENT FOR MULTICELL/LINEAR ORGANIZATION -- AND PERHAPS

LOW-LEVEL ROTATION ALONG THE WARM FRONTAL ZONE WHERE SURFACE WINDS

ARE BACKED.  THOUGH AN ISOLATED/BRIEF TORNADO WILL BE POSSIBLE NEAR

THIS BOUNDARY...LARGE HAIL AND LOCALLY DAMAGING WINDS WILL BE THE

MAIN SEVERE RISKS -- PARTICULARLY IF CONVECTION GROWS UPSCALE INTO

AN ORGANIZED/SOUTHWARD-MOVING CLUSTER AS CURRENTLY APPEARS POSSIBLE.



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

TO 2 INCHES. EXTREME TURBULENCE AND SURFACE WIND GUSTS TO 60

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

MOTION VECTOR 31030.





...GOSS

