Recent unseasonable warmth across the Midwest, driven by a strong upper-level ridge allowing southerly flow, kept Chicago overnight lows elevated well above the 47°F climatological normal on October 13. Official station data from O’Hare and Midway show minimums near 70°F amid light winds and limited radiational cooling under partly cloudy skies. With leading market bins clustered tightly around 64–67°F, small differences in observed cooling rates, station siting effects, and the exact timing of any late-evening wind shift create the narrow probability spreads; traders weigh these microscale factors against National Weather Service preliminary climatological reports that will determine final resolution.