Storms, 'Stifling' Heat, Humidity: New Timeline For Chicago-Area Heatwave, Severe Weather

ILLINOIS — The entire Chicago area is under a heat advisory through Thursday as dangerous heat is expected, according to the National Weather Service.

The heat advisory is in effect from 10 a.m. Wednesday to 10 p.m. Thursday. Peak heat index values of 110 are possible.

Related: Chicago Area Heat Wave: What To Know, How To Stay Cool

The weather service said stifling heat will continue in Chicago on Wednesday night, and that it "cannot rule out storms at any time." There will be little relief since heat indices will only drop below 90 degrees for a few hours, although there is a slight chance of showers and storms before 7 p.m.

"Hot temperatures and high humidity may cause heat illnesses," the weather service said. The agency advised drinking plenty of fluids, staying in an air-conditioned room, staying out of the sun, and checking on relatives and neighbors.

Some of the hottest areas on Wednesday will be Rockford, Rochelle, Ottawa and Belvidere, according to the weather service.

Thursday will bring more dangerous heat and a possible heat index over 105 degrees, with relief not expected until Friday.

If you are looking for a cooling center, you can find a list of sites across the state here.

By county:

• Cook County
• DuPage County
• Grundy County
• Kane County
• Kendall County
• Lake County
• McHenry County
• Will County

Showers, Severe Storms Possible Through Saturday

It is possible that some thunderstorms could bring localized relief, especially near the Wisconsin border. Chances for storms will increase across the area on Thursday and Friday, with the heat easing on Friday.

The threat of storms increases Thursday afternoon and evening.

Any storms on Thursday afternoon and evening could be severe, and contain torrential rainfall, according to the weather service. Additional periods of slow-moving storms are expected late Thursday night through Saturday "will contain torrential rainfall and may produce localized flooding," NWS said.

Here's a look at the forecast:

Wednesday - A slight chance of showers before noon, then a slight chance of showers and thunderstorms after 3pm. Mostly sunny, with a high near 93. Heat index values as high as 103. South wind 10 to 15 mph, with gusts as high as 20 mph. Chance of precipitation is 20%.

Wednesday night: A 10 percent chance of showers and thunderstorms before 7pm. Mostly clear, with a low around 80. South southwest wind around 10 mph, with gusts as high as 15 mph.

Thursday: A 40 percent chance of showers and thunderstorms after 1 pm. Mostly sunny and hot, with a high near 97. Heat index values as high as 107. Southwest wind 10 to 15 mph, with gusts as high as 20 mph.

Thursday night - Showers and thunderstorms likely before 1 am, then showers likely and possibly a thunderstorm after 1am. Mostly cloudy, with a low around 74. West southwest wind 5 to 10 mph, with gusts as high as 15 mph. Chance of precipitation is 70%.

Friday - A 50 percent chance of showers and thunderstorms. Mostly cloudy, with a high near 81. West wind 5 to 10 mph becoming northeast in the afternoon.

Friday night - A chance of showers and thunderstorms, then showers likely and possibly a thunderstorm after 1am. Mostly cloudy, with a low around 71. Chance of precipitation is 60%.