National Weather Service United States Department of Commerce

Hot and humid air will dominate the area through Monday, and linger south of I-70 on Tuesday. Thunderstorm complexes moving around the edge of the heat dome will bring periodic thunderstorm chances, with the highest coverage of storms expected on Tuesday when a cold front moves through.
A Heat Advisory is in effect through Monday across central and southeast Illinois. Heat index values of 100 to 110 are expected both afternoons, and only drop off into the 75-80 degree range at night. There is some potential for this to be extended into Tuesday, especially south of I-72, but will be dependent on the track of thunderstorms to our north Monday night. If you have to be outside, wear light weight and light colored clothing, and try to do your work early or late in the day.
Thunderstorm clusters will dive southeast from the Upper Midwest tonight and Monday night, on the edge of a hot airmass over the central U.S. While there is uncertainty on timing and placement of these storm complexes, they could affect northern portions of central IL. Damaging wind gusts are the primary risk.