SPC MESOSCALE DISCUSSION 1815 FOR IL AND IN
CONCERNING...SEVERE THUNDERSTORM POTENTIAL...

A TORNADO WATCH MAY BE REQUIRED ACROSS PORTIONS OF CENTRAL IL INTO
NWRN IND IN THE NEXT HOUR.

UPPER LOW IS DIGGING SEWD ACROSS SERN MN INTO NERN IA ATTM.
DOWNSTREAM...LOW LEVELS ARE BEGINNING TO RESPOND WITH SURFACE LOW
REORGANIZING OVER WCNTRL IL NEAR UIN...WITH AN INTENSIFYING E-W
WARM FRONT ACROSS CENTRAL IL INTO WRN OH.  LOW LEVEL WARM ADVECTION
HAS MAINTAINED ELEVATED BROAD BAND OF CONVECTION NORTH OF BOUNDARY
OVER IL...AND WILL CONTINUE TO AID CONVECTION AS IT SHIFTS EWD.  AS
LAPSE RATES STEEPEN FROM CENTRAL IL INTO NWRN INDIANA...EXPECT A
GRADUAL INTENSIFICATION ALONG LEADING EDGE OF CURRENT ACTIVITY
...WITH ADDITIONAL CONVECTION ALONG E-W BOUNDARY IN THE NEXT FEW
HOURS AS BOUNDARY LAYER WARMS.  VERTICAL SHEAR AND INSTABILITY
APPEAR TO BE SUFFICIENT FOR SUPERCELLS...WITH A THREAT OF LARGE
HAIL...DAMAGING WINDS...AND POSSIBLY TORNADOES.

..DARROW.. 08/18/01