CHICAGO (CBS) — The heat is on. After thunderstorms delayed the arrival of a heat wave on Thursday, temperatures are on the rise, and Friday is expected to be the hottest day of the year, with a high near 100 degrees.

The National Weather Service has issued an excessive heat warning, starting at 10 a.m. Friday, and continuing through Saturday at 7 p.m.

Temperatures are expected to reach about 98 on Friday and about 96 on Saturday. With the humidity factored in, it could feel as hot as 113 in Chciago by Friday evening. Some suburbs could have heat index values close to 120.

While it’s unlikely Friday or Saturday’s high temperatures will set any records, Chicago already might have set a different temperature record for the day on Friday.

As of 7 a.m., the low temperature at O’Hare was 81. The record for hottest minimum temperature for Chicago on July 19 is 78, set in 2011. Temperatures are not expected to drop below 80 again until sometime Saturday night or Sunday morning.

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Thankfully, a powerful cold front will come through on Sunday, bringing temperatures down significantly, with temperatures ranging from the low 60s to mid 80s the rest of the 7-day forecast.