Traders have overwhelmingly priced 62-63°F as the highest temperature recorded in Chicago on September 22 because official NOAA station observations and National Weather Service summaries confirmed a daily maximum in that narrow range. This outcome aligns with the arrival of a cooler air mass behind a passing frontal boundary that suppressed afternoon heating across the Midwest, keeping readings below the late-September climatological average near 70°F. Verified surface data released shortly after the observation window eliminated nearly all uncertainty, producing the near-100% market-implied probability. Only an unusually large post-analysis correction to the official record could alter the result, an infrequent occurrence once preliminary measurements undergo quality control.