Official National Weather Service observations at Chicago O'Hare recorded a daily maximum of 69°F on September 20, 2026, under overcast skies with light easterly flow and elevated humidity, placing the reading just below the 70-71°F bin that now commands full market-implied probability. This outcome aligns with cooler-than-normal conditions following a stretch of late-summer warmth, consistent with regional model guidance showing suppressed temperatures from persistent cloud cover and onshore flow off Lake Michigan. Minor station-to-station differences, such as at Midway Airport, or final quality-controlled adjustments could theoretically shift the exact bin, though historical verification processes make such revisions unlikely once preliminary data are confirmed.