Official National Weather Service observations at Chicago O’Hare recorded a daily maximum of 70°F on September 30, 2026, matching the long-term climatological normal of 70.6°F and aligning precisely with the market’s 70-71°F resolution bin. Persistent cloud cover, widespread rain totaling over half an inch, and southerly flow tied to remnant tropical moisture suppressed daytime warming and kept temperatures from exceeding this narrow range. Preliminary climatological summaries and multiple station reports converged on the same value, producing near-certain market pricing. Only a post-analysis revision by NOAA, a significant discrepancy between official airport sites, or an unreported localized anomaly could alter the outcome at this stage.