A Heat Advisory took effect across nearly all of the Chicago area Monday morning, warning of heat indices of up to 109 degrees.
The advisory began at 11 a.m. for DeKalb, Kane, DuPage, Cook, LaSalle, Kendall, Will and Kankakee counties in Illinois and Lake, Porter, Newton and Jasper counties in northwest Indiana.
It remains in effect until 7 p.m.
Temperature highs were expected to rise into the low- to mid-90s, with heat indices between 103 and 109, according to the National Weather Service.
"The combination of hot temperatures and high humidity will combine to create a situation in which heat illnesses are possible," the alert states.
Residents are being urged to drink plenty of fluids, stay in air-conditioned rooms when possible, avoid the sun and check on relatives and neighbors.
A few showers and isolated storms will be possible late Monday in far north and northwest counties.