Recent National Weather Service and model guidance indicate a Thursday night low in the mid-to-upper 60s for Chicago, with most forecasts centering on 66–69 °F amid mostly cloudy skies, light northeast winds, and scattered showers that limit radiative cooling. The market’s tight clustering around the 59 °F-and-below, 66–67 °F, and 68–69 °F bins reflects uncertainty in how much further temperatures may fall if clouds clear overnight or if steering flow allows slightly cooler air advection. Historical September 17 averages near 58 °F provide context, yet persistent humidity and weak pressure gradients this week have kept overnight minima several degrees above climatology. Updated model runs and the evening forecast discussion will likely resolve the narrow spread between these leading outcomes before resolution.