Official National Weather Service observations at Chicago O’Hare recorded a maximum temperature of 64 °F on September 25, 2026—eight degrees below the 1991–2020 normal—under persistent cloud cover that limited daytime warming. This verified value produced the market’s 100 % consensus on the 64–65 °F bin, as traders aligned positions with the authoritative climatological report rather than forecasts. Minor residual probabilities on adjacent bins reflect only the remote chance of final data revisions or station discrepancies before market resolution. Upcoming NWS confirmation or any post-event quality-control adjustments remain the only plausible catalysts that could shift the near-certain outcome.