Mesoscale Discussion 1581
   NWS Storm Prediction Center Norman OK
   0218 PM CDT Mon Aug 23 2021

   Areas affected...Parts of west central into southwestern Illinois
   and adjacent portions of east central Missouri

   Concerning...Severe potential...Watch unlikely 

   Valid 231918Z - 232115Z

   Probability of Watch Issuance...20 percent

   SUMMARY...There appears at least some possibility for the evolution
   of an increasingly organized cluster of thunderstorms, which could
   pose a risk for potentially damaging wind gusts near or just east of
   the Greater St. Louis metropolitan area by 4-6 PM CDT.  It is not
   clear that a severe weather watch will be needed, but trends are
   being monitored.

   DISCUSSION...Thunderstorm activity has recently intensified near the
   intersection of southward advancing convective outflow and a remnant
   low-level baroclinic zone extending across west central Illinois. 
   This likely has been aided by inflow of very moist boundary layer
   air (with surface dew points in the mid/upper 70s F), which appears
   characterized by large CAPE up to around 3000 J/kg.  In the presence
   of modest shear, largely due to veering of ambient winds from
   southwesterly in low-levels to westerly in mid-levels, southerly
   low-level system-relative inflow appears moderately strong, on the
   order of 15-20 kts.  It appears that this may contribute to
   continuing southward propagation toward at least eastern portions of
   the Greater St. Louis metro area during the next few hours.  

   Latest objective instability analysis suggests that the southward
   propagation will coincide with the axis of largest mixed-layer CAPE,
   along the eastern periphery of warmer and more strongly capping
   elevated mixed-layer air emanating from the Great Plains.  Given the
    degree of CAPE, coupled with additional steepening of already
   modestly steep low-level lapse rates, there appears at least some
   potential for further intensification and upscale growth of the
   cluster of thunderstorms, which could be accompanied by increasing
   risk to produce potentially damaging surface gusts.

   ..Kerr/Dial.. 08/23/2021

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

   ATTN...WFO...ILX...LSX...

   LAT...LON   39708948 38968873 38388992 39409075 39619018 39708948