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WWUS20 KWNS 121754

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URGENT - IMMEDIATE BROADCAST REQUESTED

SEVERE THUNDERSTORM WATCH NUMBER 301

NWS STORM PREDICTION CENTER NORMAN OK

1250 PM CDT SAT JUN 12 2010



THE NWS STORM PREDICTION CENTER HAS ISSUED A

SEVERE THUNDERSTORM WATCH FOR PORTIONS OF



       CENTRAL ILLINOIS

       NORTHWEST INDIANA

       EXTREME NORTHEAST MISSOURI



EFFECTIVE THIS SATURDAY AFTERNOON AND EVENING FROM 1250 PM UNTIL

700 PM CDT.



HAIL TO 2.5 INCHES 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 135

STATUTE MILES EAST AND WEST OF A LINE FROM 15 MILES WEST

NORTHWEST OF VALPARAISO INDIANA TO 20 MILES SOUTH SOUTHEAST OF

SPRINGFIELD ILLINOIS.  FOR A COMPLETE DEPICTION OF THE WATCH SEE

THE ASSOCIATED WATCH OUTLINE UPDATE (WOUS64 KWNS WOU1).



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...STORMS SHOULD CONTINUE TO DEVELOP WITHIN VERY UNSTABLE

AIRMASS ACROSS THE WATCH AREA THIS AFTERNOON AS WELL-DEFINED AND

CONVECTIVELY-REINFORCED COLD FRONT/COLD POOL SPREADS EWD FROM IA/MO.

IN ADDITION TO LIFT WITH THE FRONT AND COLD POOLS...ADDITIONAL

DEVELOPMENT IS OCCURRING ALONG REMNANT OUTFLOW BOUNDARY ACROSS CNTRL

IL. MLCAPE OVER 2000 J/KG AND WEAKENING INHIBITION NEAR THESE

MESOSCALE FEATURES WILL SUSTAIN ROBUST THUNDERSTORMS. SHEAR ACROSS

THE AREA IS MARGINALLY SUPPORTIVE OF SUPERCELL

STRUCTURES...ESPECIALLY FROM THE OUTFLOW BOUNDARY NWD WHERE BOTH

DIRECTIONAL SHEAR AND STRONGER SPEED SHEAR COULD SUPPORT A COUPLE OF

LONGER-LIVED SUPERCELLS WITH LARGE HAIL AND POSSIBLY EVEN A BRIEF

TORNADO. MOST OF THIS ACTIVITY WILL BE CAPABLE OF PRODUCING DAMAGING

WINDS INTO THE LAST AFTERNOON.



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

TO 2.5 INCHES. EXTREME TURBULENCE AND SURFACE WIND GUSTS TO 60

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

MOTION VECTOR 23025.





...CARBIN

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