ABC7 Accuweather Alert Meteorologist Tracy Butler said highs will again reach into the mid-90s, with a heat index of 100-103 degrees.
The National Weather Service said an Air Quality Alert is in effect for the Chicago area due to elevated ozone levels. The NWS said smoke levels may increase Wednesday night into Thursday.
The NWS said the alert may be extended depending on if smoke from Canadian wildfires reach the area.
Dr. Juanita Mora of the American Lung Association warned that elevated ozone levels, combined with the heat, can pose health risks.
"That ozone becomes like a sunburn into the lungs, and when that occurs people can start wheezing, having coughing, having respiratory problems, along from the heat, and all the dehydration that can occur," Mora said.
The Chicago Office of Emergency Management and Communications is encouraging residents to be prepared for extreme heat.
Cooling centers are expected to be open.
When the temperatures climb to extreme levels, it is important to check on relatives, neighbors, seniors and vulnerable populations. Chicago residents can call 311 for well-being checks.