The heat advisory for Cook County and other surrounding counties issued this afternoon has been canceled, but it remains in effect for several other counties in northern central Illinois, according to the National Weather Service.
The advisory remains in effect for Winnebago, Boone, Ogle, Lee, Dekalb, Lasalle and Livingston counties, according to the weather service Web site. The advisory is set to remain in effect until 9 p.m.
Temperatures are forecast to reach the middle and upper 90s, with high humidity making it feel more like 105, the weather service said.
"The combination of heat and humidity will create oppressive conditions which may cause heat-related illnesses to develop with prolonged exposure," according to the heat advisory.
As many people have outdoor plans this weekend, it is essential that sensitive groups take precautions to stay safe and limit the exacerbation of breathing problems.
The weather service also advised rescheduling strenuous activities today to early morning or early evening, and to wear light-weight and loose-fitting clothing. Also, drink plenty of water.
The city experienced three days in early June in which temperatures topped 90, but with much lower humidity levels than the current heat wave, officials said.
Saturday will also be hot, with highs in the lower 90s. The afternoon heat index will be 97 to 102. There also is a 30 percent chance of showers and thunderstorms.
On Sunday, the highs will be in the lower 80s, and on the July 4th holiday it will cool off a bit to the lower 80s.
The temperature today is not expected to challenge the 103-degree record temperature for a July 1, set in 1956.
The last time it hit 97 degrees was Aug. 2, 2006, and on July 31 and Aug. 1, 2006, it was even hotter, with a high of 99 degrees. Last year’s high was 94 degrees on July 23.
The last five 100-degree days recorded at O'Hare International Airport are:
-- July 24, 2005: 102.
-- July 30, 1999: 101.
-- July 14, 1995: 100.
-- July 13, 1995: 104.
-- Aug. 2, 1991: 101.
For the latest conditions and forecasts see the Chicago Weather Center.