Storm Prediction Center Mesoscale Discussion 1163

   Mesoscale Discussion 1163
   NWS Storm Prediction Center Norman OK
   1043 AM CDT Wed Jun 17 2026

   Areas affected...central Illinois into western Indiana

   Concerning...Tornado Watch 340...

   Valid 171543Z - 171745Z

   The severe weather threat for Tornado Watch 340 continues.

   SUMMARY...Damaging wind and tornado potential continues within
   WW340.

   DISCUSSION...Several broken thunderstorm clusters continue across
   south-central Illinois. The leading line of this convection appears
   to still be tied to the stronger cold pool/outflow producing gusts
   60-65 mph in the last hour. The air mass across southern Illinois
   into Indiana is only marginally unstable, however, temperatures are
   warming into the mid to upper 70s F under mostly sunny skies with
   dew points in the mid to upper 60s F. Additionally, the low level
   jet axis (as shown in SPC Mesoanalysis and sampled from VAD profiles
   from LSX and ILX) still extends into central/southern Illinois with
   ample deep layer shear for organization, which may overcome the more
   marginal air mass. Hi-res CAM guidance suggests this cluster will
   weaken with time into eastern Illinois. Though guidance suggests
   weakening, the continued low-level jet influence and heating ahead
   of the line leads to low confidence in exactly when severe potential
   will decrease downstream. Trends will be monitored, with potential
   for a watch to be issued downstream of WW340.

   Within WW340, tornado potential continues along the southern edge of
   the current ongoing cluster. Here, more favorable low-level shear
   may support a tornado or two within more discrete cells.

   ..Thornton/Hart.. 06/17/2026

   ...Please see www.spc.noaa.gov for graphic product...

   ATTN...WFO...IND...LOT...ILX...LSX...

   LAT...LON   39649038 40128976 40508902 40528786 40078711 39678708
               39268703 38808724 38798920 39219031 39649038 

   MOST PROBABLE PEAK TORNADO INTENSITY...100-125 MPH
   MOST PROBABLE PEAK WIND GUST...65-80 MPH
   MOST PROBABLE PEAK HAIL SIZE...1.00-1.75 IN