Mesoscale Discussion – possible strong thunderstorms over northern Illinois this Sunday evening

Weather
Mesoscale Discussion 1346
   NWS Storm Prediction Center Norman OK
   0533 PM CDT Sun Jul 26 2020

   Areas affected...far eastern IA...northern IL...southern WI and
   portions of northern Lower MI

   Concerning...Severe potential...Watch unlikely 

   Valid 262233Z - 270000Z

   Probability of Watch Issuance...20 percent

   SUMMARY...Strong storms capable of gusts as high as 50 mph may
   continue for another couple of hours this evening before weakening.
   A severe thunderstorm watch is not expected.

   DISCUSSION...A line of strong to isolated severe thunderstorms
   stretches from ear east-central IA northeastward through southern WI
   into northern Lower MI. These storms are occurring in a weakly to
   moderately unstable environment with MLCAPE values from 1500-2500
   J/kg. Steep low level lapse rates and high PW values near 2 inches
   will largely support strong downburst winds. While the downstream
   airmass will remain unstable, weak effective shear and poor midlevel
   lapse rates will limit the longevity of the this organized line.
   Most recent radar data from KMKX shows an outflow boundary is
   currently surging ahead of the main line of storms. This will
   further act to weaken convection in the absence of a stronger cold
   pool and developing rear-inflow jet. Due to these factors,
   convection is likely near peak intensity and is expected to
   gradually weaken with south/southeastward extent over the next few
   hours.

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