MESOSCALE DISCUSSION 0507
   NWS STORM PREDICTION CENTER NORMAN OK
   0821 PM CDT WED APR 17 2013
   
   AREAS AFFECTED...CNTRL IL INTO PORTIONS OF CNTRL/NRN INDIANA
   
   CONCERNING...TORNADO WATCH 118...
   
   VALID 180121Z - 180245Z
   
   THE SEVERE WEATHER THREAT FOR TORNADO WATCH 118 CONTINUES.
   
   SUMMARY...THE SVR THREAT CONTINUES ACROSS REMAINING VALID PORTIONS
   OF WW118.
   
   DISCUSSION...IN NRN INDIANA...ONE CLUSTER OF WAA-RELATED CONVECTION
   CONTINUES TO ADVANCE NWD/EWD AWAY FROM ANY RESIDUAL BOUNDARY-LAYER
   BUOYANCY RESIDING S OF A QUASI-STATIONARY FRONT STRETCHING FROM
   W-CNTRL OHIO WWD INTO CNTRL IL AND CNTRL MO. ASIDE FROM A RISK FOR
   MARGINALLY SVR HAIL...THIS ACTIVITY SHOULD WEAKEN AS IT BECOMES
   INCREASINGLY ELEVATED...AND BUOYANCY ATOP THE SFC COLD DOME WEAKENS
   WITH NOCTURNAL COOLING.
   
   ADDITIONAL CLUSTERS OF CONVECTION UPSTREAM ACROSS NERN MO...W-CNTRL
   IL...AND SERN IA WILL CONTINUE SPREADING ENEWD...POTENTIALLY
   ORGANIZING INTO ONE OR MORE ORGANIZED LINES OF STORMS. THIS ACTIVITY
   WILL LIKELY REMAIN ELEVATED TO THE N OF THE SFC FRONT...WHERE STRONG
   STATIC STABILITY IS NOTED IN THE LOWEST 1 KM AGL PER THE ILX 00Z
   RAOB. NEVERTHELESS...STRONG 0-6-KM SHEAR WILL MAINTAIN ORGANIZED
   CONVECTION...WITH SVR HAIL BEING THE PRIMARY CONCERN. HOWEVER...SVR
   WINDS CANNOT BE RULED OUT IF DOWNDRAFTS CAN PENETRATE THROUGH THE
   STABLE LAYER TO THE SFC...ESPECIALLY WITH ELEVATED BOWING LINE
   SEGMENTS/SUPERCELLS. VERY SMALL TEMPERATURE-DEWPOINT SPREADS IN THE
   LOW LEVELS...AND ONLY MODEST MID-LEVEL LAPSE RATES...WILL GREATLY
   MITIGATE SUCH POTENTIAL.
   
   ..COHEN.. 04/18/2013
   
   
   ATTN...WFO...IWX...IND...LOT...ILX...LSX...DVN...
   
   LAT...LON   40378603 39938652 39388846 39348975 39589051 40249050
               40949002 41098925 41118635 40378603