Watch Likely for Parts of Stateline

This discussion on a possible watch to be issued by the SPC out of Norman, OK:

MESOSCALE DISCUSSION 1344
NWS STORM PREDICTION CENTER NORMAN OK 0456 PM CDT TUE JUN 21 2011

AREAS AFFECTED...PARTS OF NRN IL...NRN AND CNTRL IND
CONCERNING...SEVERE POTENTIAL...WATCH POSSIBLE
VALID 212156Z - 212330Z
AN ADDITIONAL WW MAY BE NEEDED WITHIN THE NEXT HOUR OR TWO.

LOW-LEVEL CONVERGENCE IN THE WARM SECTOR OF THE OCCLUDING LOW OVER THE UPPER MISSISSIPPI VALLEY IS GENERALLY WEAK...BUT 30-40 KT SOUTHERLY DEEP LAYER FLOW AND SHEAR IS AT LEAST MODESTLY STRONG SOUTHEAST OF THE CYCLONE...OVER MUCH OF MISSOURI INTO ILLINOIS. MID-LEVEL LAPSE RATES ARE ALSO STEEPEST ACROSS THAT SAME REGION... BUT MIXED LAYER CAPE HAS BECOME LARGE OVER MUCH OF OHIO VALLEY/SOUTHERN GREAT LAKES REGION IN THE PEAK AFTERNOON HEATING.

A DEVELOPING COLD POOL ASSOCIATED WITH AN EVOLVING MESOSCALE
CONVECTIVE SYSTEM SEEMS TO OVER THE BEST POTENTIAL FOR AN ORGANIZED SEVERE WEATHER THREAT ACROSS INDIANA...AS IT SPREADS ACROSS THE INTERSTATE 70 CORRIDOR...INCLUDING INDIANAPOLIS DURING THE 00-02ZTIME FRAME. OTHERWISE...IN A SOMEWHAT BETTER SEVERE WEATHER ENVIRONMENT...VIGOROUS CONVECTION WILL PROBABLY CONTINUE TO DEVELOP NORTHWARD OUT OF CENTRAL ILLINOIS THROUGH THE REMAINDER OF ILLINOIS DURING THE REMAINDER OF THE AFTERNOON AND EVENING.