336 ACUS11 KWNS 212138 SWOMCD SPC MCD 212137 ILZ000-INZ000-KYZ000-220000- SPC MESOSCALE DISCUSSION 0476 FOR...SRN IL/IN AND NRN KY... CONCERNING...TORNADO WATCH 139...SEVERE THUNDERSTORM WATCH 137... CLUSTER OF LONG-LIVED SUPERCELLS OVER WAYNE AND HAMILTON COUNTIES WERE MOVING ESEWD TOWARD THE WABASH RIVER AND WILL TRACK INTO SRN INDIANA NEAR AND NORTH THE OH RIVER BY 22Z. MOST INTENSE STORM ATTM WAS MOVING TOWARD GALLATIN AND WHITE COUNTIES OF SERN IL AND THIS ACTIVITY WAS COLOCATED WITH DEEPENING SURFACE LOW ALONG STRONG FRONTAL ZONE. WELL-DEFINED 2-HOUR RISE/FALL COUPLET WAS ALSO ANALYZED IN MESOSCALE PRESSURE FIELD WITH STRONGEST FALLS OVER SWRN INDIANA. AIRMASS AHEAD OF THIS ACTIVITY INTO NRN KY WILL REMAIN FAVORABLE FOR INTENSE UPDRAFTS PRODUCING LARGE HAIL AND DAMAGING WINDS. GREATEST TORNADIC POTENTIAL WILL CONTINUE TO EXIST WITHIN A NARROW CORRIDOR COINCIDENT WITH THE TRACK OF THE SURFACE LOW ALONG TIGHT LOW LEVEL BAROCLINIC ZONE. WT 139 AND WW 137 WILL LIKELY NEED TO BE REPLACED PRIOR TO EXPIRATION FOR PARTS FOR PARTS OF SRN INDIANA...NRN KY...AND EXTREME SRN IL. ..CARBIN.. 04/21/02