Mesoscale Discussion – potential severe storms across northern Illinois
Mesoscale Discussion 1546 NWS Storm Prediction Center Norman OK 0159 PM CDT Sat Jul 20 2019 Areas affected...Portions of northern Illinois and Chicagoland Area Concerning...Severe potential...Watch possible Valid until 4PM CDT... Probability of Watch Issuance...40 percent SUMMARY...As thunderstorms/outflow near northern Illinois, intense convection is possible given the extreme buoyancy in the area. Uncertainty remains as to how far south ongoing/newly developing convection will push into northern Illinois. A WW is possible should convective trends become more clear. DISCUSSION...A relatively narrow corridor of undisturbed airmass remains in far southern Wisconsin and northern Illinois. Temperatures have risen into the upper 80s F to low 90s F with dewpoints holding in the upper 70s F. Two ongoing linear segments in southwestern and southeastern Wisconsin will likely continue to sag slowly southward with time. Given the extreme buoyancy -- MLCAPE of 4000+ J/kg -- intense convection is possible with damaging winds being the primary threat. With the low-level shear vector oriented nearly parallel to the outflow, it is uncertain how much development will occur southward into Illinois. However, HCRs are currently visible on visible satellite imagery in northeastern Illinois. Even subtle lift from the outflow boundary may allow parcels to reach their LFC. A WW is possible should trends reveal convection is more likely.