MESOSCALE DISCUSSION 0518
   NWS STORM PREDICTION CENTER NORMAN OK
   0725 AM CDT THU APR 18 2013
   
   AREAS AFFECTED...ERN IL...MUCH OF INDIANA...SWRN LOWER MI
   
   CONCERNING...SEVERE POTENTIAL...WATCH LIKELY 
   
   VALID 181225Z - 181400Z
   
   PROBABILITY OF WATCH ISSUANCE...80 PERCENT
   
   SUMMARY...LINE OF THUNDERSTORMS WILL ADVANCE EWD ACROSS ERN IL INTO
   INDIANA AND SWRN LOWER MI THIS MORNING...WITH SVR THREAT EXPECTED TO
   INCREASE WITH TIME. ALTHOUGH A WW IS NOT IMMEDIATELY NECESSARY...ONE
   WILL LIKELY BE ISSUED LATER THIS MORNING.
   
   DISCUSSION...SURFACE LOW PRESSURE CONTINUES TO ADVANCE NEWD ACROSS
   THE MID MS VALLEY THIS MORNING AHEAD OF A SHORTWAVE TROUGH EJECTING
   OVER THE CNTRL PLAINS. LINE OF THUNDERSTORMS OCCURRING AHEAD OF THE
   SURFACE LOW IS CURRENTLY MOVING EWD ACROSS CNTRL IL WITHIN A WEAKLY
   UNSTABLE AIRMASS. HOWEVER...LATEST SURFACE OBSERVATIONS AND
   OBJECTIVE ANALYSIS GUIDANCE INDICATE INCREASING THETA-E VALUES AHEAD
   OF THE LINE OVER ERN IL AND WRN INDIANA. IN ADDITION...EARLY VISIBLE
   SATELLITE IMAGERY SHOWS MAINLY CLEAR SKIES ACROSS INDIANA...WHICH
   WILL FURTHER AID IN BOUNDARY LAYER DESTABILIZATION WITH CONTINUED
   DAYTIME HEATING. GIVEN THE PRESENCE OF 60+ KT OF DEEP-LAYER SWLY
   FLOW OVERSPREADING THE AREA...THE THREAT FOR DAMAGING WIND GUSTS AND
   A COUPLE OF TORNADOES IS EXPECTED TO INCREASE THIS MORNING.
   
   ..GARNER/HART.. 04/18/2013
   
   
   ATTN...WFO...IWX...GRR...IND...PAH...LOT...ILX...LSX...
   
   LAT...LON   39828903 41828776 42388506 40108523 38528691 38408927
               39828903