Recent forecasts from the National Weather Service and supporting models point to a minimum temperature in Chicago on September 15, 2026, likely falling in the mid-to-upper 60s °F, with trader consensus tightly clustered across the 62–69 °F bins reflecting model spread and timing uncertainty. Southwesterly winds of 10–20 mph, elevated humidity near 70–85 %, and scattered showers or thunderstorms have limited radiational cooling overnight, while a gradual wind shift toward the north-northeast after midnight could allow modest further drops. Cloud cover and warm-air advection from the south maintain the floor above historical September averages near 59 °F, yet any earlier clearing or lighter winds could push readings toward the lower 60s. Updated NWS guidance and hourly observations through the morning will clarify whether the minimum settles near 64–65 °F or holds closer to 68–69 °F.