Severe storm potential exists this afternoon and evening to the south and west of the Chicago area. A Tornado Watch remains in effect for central Illinois until 6PM CDT. Following is a Mesoscale Discussion issued by the National Storm Prediction Center describing a potential for severe storm development to our west in Iowa and western Illinois and the possibility of the issuance of a Tornado Watch for that area.
Mesoscale Discussion 0772 NWS Storm Prediction Center Norman OK 0325 PM CDT Fri May 24 2019 Areas affected...Eastern IA...Far Southwest WI...Far Northwest IL Concerning...Severe potential...Watch possible Valid 242025Z - 242130Z Probability of Watch Issuance...60 percent SUMMARY...A watch may be needed within the next few hours as storms increase in coverage across eastern IA, far southwest WI, and far northwest IL. These storms will be capable of all severe hazards, including a couple of tornadoes. DISCUSSION...Recent surface analysis places an occluded front arcing from west-central MN into central IA and then back southwest into far northeast KS. A warm front intersects this occluded front near BNW (in central IA) and then extends southeastward through central IL. Warm sector across southern IA/northern MO is characterized by temperatures in the upper 70s/low 80s and dewpoints in the upper 60s/low 70s. Expectation is for the warm front to continue lifting northward through central/east-central IA and northern IL over the next several hours. Air mass along and south of the warm front is expected to destabilize as temperatures climb into the 80s. RAP forecast soundings indicate an uncapped air mass with over 1500 J/kg of MLCAPE will exist across much of central/eastern IA by 21-22Z. Some minimal convective inhibition may persist across northern IL/southern WI until closer to 00Z. Convective initiation is expected within the next hour or two, likely along the occluded front or near the warm front. There is some uncertainty regarding storm coverage, but overall environment suggests that the storms that do form will likely be severe. All hazards are possible, including tornadoes.