Recent National Weather Service observations and model consensus from the Chicago area indicate a minimum temperature of 64-65°F on September 7, driven by a stable high-pressure system promoting gradual nocturnal cooling under clear to partly cloudy skies with light winds. This aligns closely with seasonal normals near 62°F while reflecting the influence of residual warmth from an earlier heat wave that limited radiative cooling. Official data from stations like Midway and O'Hare show overnight lows in this narrow band, with minimal model spread among short-range guidance reducing uncertainty. The 98% market-implied probability reflects traders' confidence in these verified readings and climatological context, though rare measurement revisions or station-specific microclimate variations could theoretically shift resolution if final certified data differ.