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.