Chicago, Illinois – A cooler stretch across northern Illinois will come to an end as dangerous heat and oppressive humidity return Sunday, bringing heat index values well above 100 degrees and the potential for thunderstorms that could become severe through Monday evening.
According to the National Weather Service in Chicago, Saturday will remain mostly cloudy, more humid, and seasonably cool, with afternoon highs ranging from 74 to 82 degrees. Conditions change quickly Sunday as highs climb into the mid-80s to lower 90s, while heat index values reach 100 to 105 degrees. By Monday, afternoon heat index values could rise to 100 to 110 degrees, making it the hottest period of the forecast.
The return of heat will also increase the chance for thunderstorms beginning late Sunday and continuing through Monday evening. While the exact timing, coverage, and location of storms remain uncertain, forecasters warn that some thunderstorms could become severe. Storms may produce damaging wind gusts, frequent lightning, torrential rainfall, and localized flooding, especially if multiple rounds develop.
Communities across the Chicago metro area, including Aurora, Joliet, Elgin, Waukegan, Naperville, and northwest Indiana, should prepare for dangerous heat before storms arrive. Travelers along Interstates 55, 57, 80, 88, 90, and 94 should monitor changing conditions, particularly during Monday’s afternoon commute.
Residents are urged to stay hydrated, limit strenuous outdoor activity during the hottest part of the day, and check on older adults, young children, and anyone without reliable air conditioning. Have multiple ways to receive weather warnings as thunderstorms develop, especially Monday when severe weather potential is expected to be greater.
Additional forecasts, heat headlines, or severe thunderstorm watches may be issued as confidence increases in the timing and intensity of the storms.
Forecast for Chicago, Illinois
- Saturday: High 74–82°, low 67–73°. Mostly cloudy and more humid. A few morning sprinkles possible south of I-80.
- Sunday: High 86–92°, low 72–79°. Very humid with 20–50% chance of thunderstorms. Heat index 100–105°.
- Monday: High 88–94°, low 68–73°. Very humid with thunderstorms possible, especially in the evening. Heat index 100–110°.
- Tuesday: High 83–89°, low 64–71°. Partly cloudy with cooler conditions near Lake Michigan and a high swim risk at area beaches.
