Forecast models from sources including the National Weather Service indicate a warm, humid southerly flow over Chicago on September 15, 2026, with highs in the low-to-mid 80s°F and overnight lows most likely in the mid-to-upper 60s°F amid scattered showers and thunderstorms. This setup limits radiative cooling through persistent cloud cover and elevated dew points, keeping minimum temperatures from dropping as sharply as the long-term September average near 59°F. Trader consensus clustering on 66–69°F bins reflects model agreement on these conditions, while the notable share assigned to 78°F or higher captures uncertainty over whether heavier rain or thicker clouds could suppress cooling further. Key variables include the exact timing of any clearing and wind speeds overnight, which official updates will refine before resolution.