Updated severe weather outlook for the Chicago area
Latest forecasts indicate the Enhanced area of severe storms during the next 24 hours will extend more to the east out of Wisconsin into Lower Michigan. For the Chicago area the Slight Risk of severe storms has been shifted north to include counties adjacent to the Illinois/Wisconsin border with a good portion of the remaining Chicago area under a Marginal Risk (see highlighted updated severe weather outlook map).
A few widely scattered/isolated thunderstorms may occur this afternoon over our area with the main threat of strong to severe storms later this evening into the overnight hours in advance of the cold front approaching from the northwest.
With very warm humid air in place and a cold front moving southeast through Wisconsin, conditions will be ripe for strong to severe storms to develop and/or spread over our area later today and tonight. The National Storm Prediction Center outlook (see highlight map) has northern Illinois and northwest Indiana under a slight to Marginal risk of severe storms with the primary threat being large hail, damaging winds and localized flood-producing downpours. The Slight Risk (yellow-shaded area depicting a 15% chance of severe storms within 25 miles of a given location) covers most of our area north of Interstate-80. The remainder of the area into central Illinois and Indiana is under a Marginal risk (dark-green-shaded area depicting a 5% chance of severe storms within 25 miles of a given location. The greatest Enhanced Risk (tan-colored 30% chance) is over central and northern Wisconsin.
While scattered storms could develop at anytime during the afternoon here, moving from northwest to southeast, the cold front along with an upper-level disturbance will be the primary triggers for the severe storms with widespread showers thunderstorm activity spreading out along and ahead of the front. The front will probably cross the Illinois-Wisconsin state line later tonight, moving through Chicago early Friday morning, the main threat here may be later this Thursday evening.
Monitor updates on this developing situation and keep an eye on latest weather radar reports.