499
ACUS3 KMKC 161940
SWOMCD
MKC MCD 161939
ILZ000-INZ000-162200-

SPC MESOSCALE DISCUSSION 0754 FOR
CONCERNING...SEVERE THUNDERSTORM POTENTIAL...


THUNDERSTORM DEVELOPMENT IS POSSIBLE ACROSS PARTS OF CENTRAL / NERN
IL AND W CENTRAL / NWRN IND OVER THE NEXT 1 TO 3 HOURS.  WW MAY BE
REQUIRED IF CONVECTION DOES INITIATE.

A MOSTLY CLEAR SKY ACROSS THE REGION HAS ALLOWED SURFACE
TEMPERATURES TO HEAT INTO THE UPPER 70S TO LOW 80S ACROSS W CENTRAL
AND NWRN IND AND INTO THE MID 80S TO LOW 90S IN CENTRAL / NERN IL.
WITH DEWPOINTS IN THE MID 60S TO LOW 70S AND LOW- TO MID-LEVEL
LAPSE RATES NEAR 7 C/KM...ATMOSPHERE HAS BECOME STRONGLY UNSTABLE
WITH 2500 TO 3500 J/KG SURFACE-BASED CAPE.  ETA SOUNDINGS VALID
EARLY THIS AFTERNOON AND LIMITED CUMULUS DEVELOPMENT SUGGEST CAP
REMAINS INTACT...HOWEVER CONTINUED HEATING ALONG WITH WEAK LOW-
LEVEL CONVERGENCE ALONG VARIOUS BOUNDARIES AND THE APPROACHING COLD
FRONT MAY BE SUFFICIENT FOR STORM INITIATION BETWEEN NOW AND 22Z.

ALTHOUGH DEEP-LAYER SHEAR 35 TO 40 KTS EXISTS ACROSS IND ATTM WHICH
IS SUFFICIENT FOR STORM ORGANIZATION...SHEAR WEAKENS WWD INTO IL
WHERE MID-LEVEL FLOW IS WEAKER.  HOWEVER...GIVEN STRONG
INSTABILITY...SOME THREAT FOR ORGANIZED STORMS / MID-LEVEL UPDRAFT
ROTATION ACROSS THIS REGION ASSUMING STORM DEVELOPMENT.  GREATEST
SEVERE THREAT WOULD LIKELY BE LARGE HAIL...ALTHOUGH DAMAGING WINDS
WOULD ALSO BE POSSIBLE -- PARTICULARLY ACROSS ERN PORTIONS OF THE
REGION WHERE DEEP-LAYER WIND FIELD IS STRONGER.

..GOSS.. 05/16/01