Official National Weather Service observations at Chicago O’Hare recorded a daily maximum of 71°F on October 9, 2026, five degrees above the 1991–2020 normal and well below historical records near 86–87°F. This value aligns with prevailing southerly flow, elevated dew points near 55°F, and persistent cloud cover that suppressed afternoon heating while light rain further moderated temperatures. The market’s near-certain pricing on the 70–71°F bin reflects traders’ confidence in these verified station data over model forecasts issued days earlier. A realistic challenge would require an official revision of the O’Hare reading or a resolution rule favoring a different station whose high fell outside that narrow range.