Official National Weather Service observations from Chicago O’Hare recorded a maximum temperature of 78°F on September 29, 2026, directly anchoring the market’s 100% implied probability on the 78–79°F outcome. This value exceeded the 1991–2020 climatological normal of 70°F yet remained well below the date’s all-time record of 99°F set in 1953. Light southwesterly winds, clear skies, and a dry airmass supported modest daytime heating without triggering stronger warm advection or mixing that could have pushed readings higher. Preliminary data from the primary reporting station show no discrepancies likely to alter the final climate summary, though minor revisions at secondary sites remain theoretically possible before official monthly verification.