Storm Prediction Center Mesoscale Discussion 1742

   Mesoscale Discussion 1742
   NWS Storm Prediction Center Norman OK
   0152 PM CDT Sun Jul 26 2026

   Areas affected...Illinois and portions of far southwest Indiana and
   western Kentucky

   Concerning...Severe potential...Watch possible 

   Valid 261852Z - 262115Z

   Probability of Watch Issuance...60 percent

   SUMMARY...Isolated convection is developing within a very unstable
   air mass over southern IL, but it is unclear when a more pronounced
   severe threat will emerge. Trends are being monitored, and watch
   issuance will likely be needed by late afternoon, though timing
   remains uncertain.

   DISCUSSION...An isolated convective cell has recently developed
   across south-central IL within a highly unstable air mass
   (characterized by MLCAPE values of 4500-5000 J/kg based on the
   recent 18 UTC DVN sounding). However, this cell is spatially
   displaced from more focused low-level convergence/forcing for ascent
   along a differential heating axis analyzed from western KY/southwest
   IN into central and northern IL. Because of this (and based on
   reflectivity trends over the past 20 minutes), it appears unlikely
   that this cell will pose much of a severe threat. 

   Recent iterations of the RRFS actually seem to be capturing
   convective trends well and depict this lone cell developing and
   decaying within the next hour or so before additional convection
   develops along the surface boundary and ahead of a subtle mid-level
   perturbation approaching from central IA during the 20-22 UTC
   period. Recent GOES imagery shows gradual cumulus growth along the
   boundary in southern IL as well as slow deepening of cumulus across
   southeast IA/northeast MO, which lends credibility to the recent
   RRFS solutions. 

   Additional convection developing later this afternoon will likely
   fully realize the favorable thermodynamic and kinematic environment
   (characterized by SCP values of 8-12) draped across central IL into
   the lower OH Valley. Guidance continues to depict relatively quick
   upscale growth into an organized MCS by early evening with an
   attendant threat for severe winds. Watch issuance will be needed
   this afternoon/evening, but exact timing will depend on when more
   widespread thunderstorm initiation becomes apparent.

   ..Moore/Leitman.. 07/26/2026

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

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

   LAT...LON   37298772 37468862 37808921 39619054 40069075 40369065
               40579034 40698988 40658934 40448890 40038844 39118771
               38618735 37928681 37598670 37388682 37278713 37298772 

   MOST PROBABLE PEAK TORNADO INTENSITY...UP TO 90 MPH
   MOST PROBABLE PEAK WIND GUST...55-70 MPH
   MOST PROBABLE PEAK HAIL SIZE...UP TO 1.25 IN