Storm Prediction Center Mesoscale Discussion 1958

   Mesoscale Discussion 1958
   NWS Storm Prediction Center Norman OK
   0433 PM CDT Wed Aug 12 2026

   Areas affected...Eastern Missouri into the lower Ohio River Valley

   Concerning...Severe Thunderstorm Watch 577...

   Valid 122133Z - 122330Z

   The severe weather threat for Severe Thunderstorm Watch 577
   continues.

   SUMMARY...Severe thunderstorms will continue to pose a severe wind
   and hail threat for the next hour or two, but should become
   increasingly sporadic through the evening hours. Downstream watch
   issuance will most likely not be required.

   DISCUSSION...The remnants of an MCS continue to push southward
   across the lower OH Valley, and although storm mode has become
   increasingly disorganized and outflow-dominant (likely a consequence
   of diminishing deep-layer wind shear with southward extent),
   lightning counts have increased over the past 20 minutes within a
   few cells from eastern MO into far southwest IN. This uptick in
   intensity comes as convection begins to push into a regional
   buoyancy maximum where MLCAPE was recently analyzed to be around
   3500 J/kg. Consequently, the potential for large hail (most likely
   around one inch) and strong/severe downburst winds should linger for
   the next 1-2 hours as convection migrates through the best
   thermodynamic environment. 

   However, regional reflectivity/velocity imagery shows that much of
   this activity is quickly becoming displaced behind a coherent
   convective outflow and/or has storm motions into the cold pool.
   Weaker deep-layer wind shear with southward extent should maintain
   the outflow-dominant nature of the convection and will eventually
   promote storm weakening and an increasingly isolated severe threat
   heading into the mid/late evening. Latest HRRR/RRFS time-lagged
   guidance captures this trend well and suggests the severe threat may
   not extend much beyond the southern bounds of WW 577. While
   convective trends will continue to be monitored as storms push
   through the buoyancy maximum, downstream watch issuance is currently
   not anticipated.

   ..Moore.. 08/12/2026

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

   ATTN...WFO...ILN...LMK...PAH...LSX...

   LAT...LON   39249129 39119068 38508854 38308798 38258739 38288658
               38408591 38598501 38698461 38718427 38588405 38378397
               38108412 37808448 37418501 37138549 36858595 36768634
               36728676 36718730 36778790 36858841 36988909 37228976
               37459026 37749081 38019124 38249156 38529182 38719193
               39129174 39249129 

   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