Chicago could see the heat index hit 115 degrees by midweek, the National Weather Service says.
Partly cloudy conditions are expected Monday and Tuesday, with temperatures in the mid- to low-80s.
But by Wednesday, temperatures in the city are expected to reach 97, which combined with 50% humidity and clear skies will make it feel between 105 and 115 degrees across the city, with higher temperatures on the outskirts and into the suburbs, National Weather Service meteorologist Kevin Doom said.
The high heat could linger into Thursday and Friday.
“The lake, unfortunately, won’t be giving much relief,” Doom told the Sun-Times on Sunday, noting that winds will be blowing offshore.
The combination of heat and humidity is expected to exceed those of the city’s June heat wave.
Wednesday’s overnight low is forecast to be 80 degrees, with Thursday’s low just a few degrees lower. The dew point will hover in the mid 70s both days, meaning little relief from humidity will arrive at night.
The chances of heat-related illnesses rise significantly during longer stretches of extreme heat and high humidity, the weather service said.
This can be especially dangerous for those without a way to cool down at night; about 11% of city residents don’t have access to air conditioning.
“That doesn’t provide a lot of relief during the night, especially for someone who doesn’t have AC to go home to at night,” Doom said. “The cumulative effects of a prolonged heat wave really add up. … [And] the heat could continue on into Friday. It’ll likely be pretty hot, we’re just not sure the extent.”
Heat and humidity builds across the region by midweek. Peak heat indices of 105 to 115 degrees are expected Wed-Thu. There are some signs that some relief from the heat may come with a cold front Fri, but uncertainty remains with this. Stay up to date on the latest forecast. pic.twitter.com/bzs8tJm5qB
— NWS Chicago (@NWSChicago) July 20, 2025
A chance of thunderstorms Thursday night, as well as a potential cold front Friday, could offer some relief, though that is not yet certain, Doom said.
Residents should be on the lookout for signs of heat effects on health. Symptoms of heat stroke and heat exhaustion include high body temperatures, headaches, dizziness, fast and weak pulse, nausea and loss of consciousness; heat exhaustion, characterized by muscle cramps, clammy skin and thirst, can lead to heat stroke if not treated.
Anyone in the city can access cooling centers and can call 311 to request welfare checks.
“Fans [alone] do not work,” Dr. Olusimbo Ige, the Chicago Department of Public Health commissioner, said at a June news conference. “If [being] indoors means no air conditioning, then a cooling location may be a safer choice.”
Some areas of the city stand to be hit harder by the heat. In a study of heat deaths and other high-temperature related emergencies released this month, city officials said the ZIP codes 60620, 60623, 60628 and 60651 saw the most calls for service during heat advisories since 2023.
Some of the areas listed are the same areas that saw the highest number of deaths during the 1995 heat wave that killed 739 people across the city, including Englewood and other majority Black neighborhoods. Largely Latino neighborhoods like Humboldt Park and parts of Austin have seen more heat emergencies in recent years.