MESOSCALE DISCUSSION 0889
   NWS STORM PREDICTION CENTER NORMAN OK
   0704 PM CDT THU MAY 30 2013

   AREAS AFFECTED...PORTIONS OF NRN-SRN IL

   CONCERNING...TORNADO WATCH 251...

   VALID 310004Z - 310100Z

   THE SEVERE WEATHER THREAT FOR TORNADO WATCH 251 CONTINUES.

   SUMMARY...A WW WILL BE COORDINATED WITH AFFECTED WFO/S ACROSS PARTS
   OF CENTRAL AND SRN IL BY 0030Z. DAMAGING WINDS AND SOME HAIL APPEAR
   TO BE THE MAIN THREATS THROUGH THE EVENING ACROSS SRN INTO CENTRAL
   IL...THOUGH A TORNADO THREAT CANNOT BE RULED OUT AS STORMS SPREAD
   E/NEWD ACROSS THE REMAINDER OF IL.

   DISCUSSION...AT 2345Z...REGIONAL RADAR IMAGERY SHOWED STRONG TO
   SEVERE STORMS IN SWRN IL /SE OF KSTL/ WITH THIS ACTIVITY TRACKING
   NNEWD AT 40 KT.  WITH EFFECTIVE BULK SHEAR OF 35-40 KT PERSISTING
   ACROSS IL THIS EVENING...THE AIR MASS DOWNSTREAM OF THIS ACTIVITY
   INTO CENTRAL AND ERN IL HAS YET TO BE CONVECTIVELY OVERTURNED. 
   THUS...DESPITE SOME WEAKENING OF INSTABILITY WITH THE LOSS OF DAY
   TIME HEATING...SUFFICIENT INSTABILITY SHOULD PROVE FAVORABLE FOR
   ADDITIONAL STRONG-SEVERE STORMS THROUGH MID-LATE EVENING /BEYOND THE
   01Z EXPIRATION OF WW 251.  ALTHOUGH EFFECTIVE BULK SHEAR DECREASES
   WITH EWD EXTENT...MODERATE INSTABILITY WILL PERSIST INTO AT LEAST
   THE MID EVENING FOR THE ERN TIER OF IL COUNTIES TO BE INCLUDED IN A
   WATCH AS WELL.

   THE LINE OF STORMS IN NRN IL SHOULD MOVE INTO WW 255 BY 01Z...SUCH
   THAT THIS PORTION OF IL MAY NOT REQUIRE A NEW WW.

   ..PETERS/KERR.. 05/31/2013


   ATTN...WFO...IND...PAH...LOT...ILX...LSX...DVN...

   LAT...LON   37478984 39399080 40858940 41828914 42468938 42458865
               40448845 40328751 38638755 37258911 37478984