**Official National Weather Service observations at Chicago O’Hare recorded a daily maximum of 92°F on September 4, 2026, reached at 2:59 p.m. CDT.** This value sits 12°F above the 1991–2020 normal high of 80°F and aligns precisely with the market’s 92–93°F bin, which reached 100% implied probability. The reading occurred amid a late-summer heat episode featuring a persistent heat dome, southerly flow, and high dew points that limited overnight cooling, producing a minimum of 76°F. While the all-time September 4 record stands at 95°F, the verified O’Hare maximum left virtually no realistic path for other bins once preliminary climatological data (CLIORD) and hourly observations circulated. Only an improbable station switch, post-hoc quality-control revision, or measurement discrepancy could have altered resolution.