Storm Prediction Center Mesoscale Discussion 1343

   Mesoscale Discussion 1343
   NWS Storm Prediction Center Norman OK
   0759 AM CDT Wed Jun 18 2025

   Areas affected...parts of central and southern Illinois...east
   central and southeastern MO...parts of northeastern
   Arkansas...adjacent western Kentucky and Tennessee

   Concerning...Severe potential...Watch possible 

   Valid 181259Z - 181500Z

   Probability of Watch Issuance...40 percent

   SUMMARY...Strong thunderstorm development may begin to initiate and
   pose increasing risk for damaging wind gusts and perhaps a couple of
   tornadoes as early as 10-11 AM CDT.  Trends are being monitored for
   the possibility of a severe weather watch.

   DISCUSSION...A significant mesoscale convective vortex, generated by
   a now largely dissipated overnight thunderstorm cluster, is
   migrating northeastward across central Missouri, with an associated
   surface low progressing across the Columbia vicinity.  This appears
   likely to continue a northeastward movement to the northwest of the
   Greater St. Louis area through mid to late morning, with a belt of
   enhanced southerly to southwesterly flow (including 40-50 Kt in the
   850-500 mb layer) to its south and east overspreading the middle
   Mississippi Valley/Mid South vicinity.  

   This will overspread a seasonably moist boundary layer, including
   surface dew points above 70F, with sufficient breaks in cloud cover
   to allow for destabilization and weakening inhibition.  The Rapid
   Refresh indicates that this may include CAPE increasing to 1000-2000
   J/kg toward midday.  At least some convection allowing guidance
   suggests that this could support the initiation of intensifying
   thunderstorm development as early as 15-16Z.  

   Given the strength of the wind fields and deep-layer shear,
   organizing thunderstorm development posing a risk for strong to
   severe wind gusts may commence.  This may include a couple of
   supercell structures, with low-level hodographs posing at least some
   risk for tornadoes, and perhaps some small to marginally severe
   hail.

   ..Kerr/Gleason.. 06/18/2025

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

   ATTN...WFO...PAH...ILX...MEG...LSX...LZK...SGF...

   LAT...LON   39479005 40148957 40068815 39188803 38128831 37398866
               36038956 35369089 35629215 37449097 38289045 39479005 

   MOST PROBABLE PEAK TORNADO INTENSITY...85-115 MPH
   MOST PROBABLE PEAK WIND GUST...55-70 MPH
   MOST PROBABLE PEAK HAIL SIZE...UP TO 1.25 IN