Official National Weather Service observations from Chicago O'Hare recorded a maximum temperature of 73°F on October 4, 2026, reached at 1:20 PM under mostly sunny skies with light winds. This value sits 5°F above the 1991–2020 normal high of 68°F and aligns precisely with pre-event model guidance anticipating lows to mid-70s amid a mild, high-pressure pattern. The market's near-certain pricing on the 72–73°F bin reflects this convergence of forecast consensus and the final verified reading at the primary resolution station. An alternative outcome would require either a substantial revision to the official climatological summary or reliance on a secondary station reporting a meaningfully different peak, both of which remain highly improbable given the stable synoptic conditions and consistent observational data.