Mesoscale discussion #486 issued for portions of the Chicago area on this evening’s severe weather threat

Weather Blog
 Mesoscale Discussion 0486
   NWS Storm Prediction Center Norman OK
   0451 PM CDT Tue Apr 28 2020

   Areas affected...Portions of southern Chicagoland and northeastern
   east-central Illinois

   Concerning...Severe potential...Watch unlikely 

   Valid 282151Z - 282345Z

   Probability of Watch Issuance...20 percent

   SUMMARY...A storm or two capable of large hail and damaging wind
   gusts will be possible for the next 1-2 hours. A storm currently in
   La Salle County may impact portions of southern Chicago and its
   suburbs by 530 PM CDT. A storm or two may also exit WW 152 and
   impact portions of east-central Illinois. Given limited buoyancy
   downstream of this activity, no WW is expected.

   DISCUSSION...A marginally organized supercell moving east through
   northern La Salle County will eventually impact portions of the
   south side of Chicago and its suburbs. 1 inch hail and estimated 60
   mph winds have already been reported with this storm. Deep-layer
   shear of around 40 kts, per KLOT VAD, is sufficient to continue
   storm oganization. MLCAPE is around 500-1000 J/kg on objective
   mesoanalysis and dwindles with eastward extent. Though other
   instances of marginally severe hail and damaging wind gusts are
   possible, the threat should remain isolated and last for the next
   1-2 hours. Farther south, another better organized supercell moving
   into Marshall County may eventually move out of WW 152 and similarly
   post a large-hail and damaging-wind threat. Buoyancy is slightly
   better farther south, but storms in this location will similarly
   encounter a less favorable thermodynamic environment to the east. A
   WW is not expected.


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