Mesoscale Discussion 1835
   NWS Storm Prediction Center Norman OK
   0609 PM CDT Mon Oct 11 2021

   Areas affected...central through northeast Illinois

   Concerning...Tornado Watch 521...

   Valid 6:09 - 7:45 PM CDT...

   The severe weather threat for Tornado Watch 521 continues.

   SUMMARY...Threat for locally strong to severe gusts and a few brief
   tornadoes will persist from central and northern IL through early
   evening.

   DISCUSSION...An arcing line storms with embedded bowing segments and
   occasional meso-vortices continues moving northeast through central
   and north central IL at 35-40 kt. The activity is moving through a
   relatively narrow instability corridor with 500-1000 J/kg MLCAPE.
   Despite the somewhat marginal thermodynamic environment, vertical
   wind profiles continue to exhibit large low-level hodographs with
   250-300 m2/s2 storm relative helicity as well as 50+ kt effective
   bulk shear. The downstream environment across northeast IL will
   remain favorable for occasional embedded organized structures
   through early evening. Storms will eventually pose a severe threat
   for the Chicago metro area near or shortly after 00Z.