The National Weather Service issued a Severe Thunderstorm Warning for Cook, Kane and DuPage counties until 6 p.m. and for Boone and Winnebago counties until 5:30 p.m. Friday.
The impacted area includes Rockford, Belvidere, Loves Park, Machesney Park, Rockton, Roscoe, Poplar Grove, Cherry Valley, Capron, Timberlane and Caledonia.
A flash flood warning was also issued for Boone and Winnebago counties until 10:30 p.m. Friday.
The warnings come as the entire Chicago area is under a heat advisory that's set to expire at 8 p.m. Saturday. The advisory took effect late Friday morning and impacts LaSalle, Grundy, Kankakee, Livingston, Iroquois and Ford counties.
Temperatures could reach into the 90s with heat indices near 110 degrees Saturday.
With the hot and steamy forecast expected to last through the next few days, the risk of severe weather is possible until Sunday.
A chance of isolated showers and thunderstorms continues on Saturday for what should otherwise be a partly sunny, hot and humid day. Highs are expected to reach the upper 80s to low 90s, but it will feel hotter with high humidity. Heat Index values could range between 100 degrees and 105 degrees.
The hot weekend continues with a hazy, hot and humid Sunday producing highs near 90 degrees and hotter heat index values. Showers and thunderstorms are possible during the morning hours.
Monday kicks off a less humid week with highs in the low- to mid-80s.