Chicago heat index could reach 100°F as September begins
Chicagoland is experiencing a surge in heat and humidity as August transitions into September. High temperatures are expected to reach the low 90s on Tuesday and Wednesday, with heat index values ranging between 95°F and 100°F (35°C to 38°C) across much of the area. Some locations south of I-80 may feel slightly hotter. Thunderstorms are possible, particularly in far-northern Illinois, but the primary concern remains the oppressive heat. Temperatures will ease slightly later in the week, with highs in the mid-to-upper 80s, which are still above average for early September. A ground stop was issued at O'Hare International Airport due to thunderstorms until 8:15 a.m. CDT on August 31, 2026. 
