Recent National Weather Service point forecasts and ensemble guidance indicate Chicago overnight lows near 55–56°F on September 26 under partly cloudy skies and light easterly flow, supporting market-implied odds clustered around the mid-50s. Key differentiating factors include modest model spread on minimum radiative cooling rates once winds calm after sunset, the influence of Lake Michigan’s moderating thermal inertia, and dewpoint values near 50°F that limit further temperature drops. Historical climatology places the average September 26 low at 54.4°F, providing a baseline against which current guidance shows only minor deviations. Final resolution depends on official observations through dawn on the 27th, when any late-night clearing or wind shifts could nudge readings a degree or two lower than currently projected.