MESOSCALE DISCUSSION 0523
   NWS STORM PREDICTION CENTER NORMAN OK
   0247 PM CDT THU APR 18 2013
   
   AREAS AFFECTED...PORTIONS NRN/WRN OH...NRN KY...SRN/CENTRAL/ERN
   INDIANA...SMALL PART OF EXTREME ERN IL.
   
   CONCERNING...TORNADO WATCH 123...
   
   VALID 181947Z - 182115Z
   
   THE SEVERE WEATHER THREAT FOR TORNADO WATCH 123 CONTINUES.
   
   SUMMARY...DESPITE WEAKENING OF CONVECTION ACROSS NRN PORTIONS OF
   THIS AREA...IN ERN INDIANA AND NWRN OH...SVR THREAT MAY INCREASE
   AGAIN AS AIR MASS DESTABILIZES AHEAD OF CONVECTION MOVING NEWD
   ACROSS SRN IL.  DAMAGING GUSTS AND BOW-ECHO/QLCS TORNADOES ARE
   POSSIBLE. ANOTHER WW IS ANTICIPATED OVER DISCUSSION AREA WITHIN NEXT
   HOUR.
   
   DISCUSSION...SFC MESOANALYSIS INDICATES OUTFLOW BOUNDARY FROM TOL
   AREA SWWD TO BETWEEN IND-GEZ...BECOMING SLOW-MOVING TO
   QUASISTATIONARY WSWWD TO JUST S HUF.  BOUNDARY POTENTIALLY FOCUSES
   ENHANCED LOW-LEVEL LIFT ALONG LEADING EDGE OF QLCS CROSSING SRN IL 
   
   PORTION OF INITIAL MCS BETWEEN MI BORDER AND CENTRAL INDIANA HAS
   DIMINISHED WITH GREATEST REFLECTIVITIES LAGGING BEHIND GUST FRONT. 
   HOWEVER...NARROW CORRIDOR OF FAVORABLE LOW-LEVEL THETAE ADVECTION IS
   FCST ACROSS THIS REGION...IN ASSOCIATION WITH 45-55 KT LLJ THAT ALSO
   WILL LENGTHEN LOW-LEVEL HODOGRAPHS AND INCREASE SRH. 
   MEANWHILE...DEW POINTS OVER SRN INDIANA HAVE LOWERED BY A FEW DEG F
   DUE TO BOUNDARY-LAYER MIXING...BUT NOT TOO MUCH TO MAINTAIN AT LEAST
   MRGL BUOYANCY ACROSS THIS REGION.  RELATED INCREASE IN DEW-POINT
   DEPRESSIONS IN MODIFIED RAOBS AND FCST SOUNDINGS YIELDS MLCAPE
   500-1000 J/KG...AMIDST 40-55 KT EFFECTIVE SHEAR MAGNITUDE.  THIS IS
   SOMEWHAT STRONGER THAN CURRENTLY EVIDENT DUE TO TWO MAIN FACTORS...
   1. EXPECTED STRENGTHENING OF DEEP-LAYER FLOW WITH TIME IN
   PRECONVECTIVE SECTOR AND
   2. DEEPENING OF BUOYANT PROFILE WITH GREATER LOW-LEVEL
   THETAE...THEREBY ADJUSTING SAMPLING DEPTH OF VERTICAL PROFILE USED
   TO COMPUTE SHEAR.
   
   ..EDWARDS.. 04/18/2013
   
   
   ATTN...WFO...CLE...ILN...LMK...IWX...IND...PAH...ILX...
   
   LAT...LON   38518813 39838763 40118667 40508515 41708412 41648279
               41468177 39918272 38658452 38508534 38518623 38518813