Official observations from Seattle-area stations recorded a daily maximum of 67°F on September 11, 2026, under mostly cloudy skies with light northwesterly winds and no significant warming aloft. This placed the high squarely in the 66-67°F bin, producing the market's near-certain 100% implied probability. National Weather Service data showed temperatures rising from morning lows near 55°F to afternoon peaks of 67°F, consistent with seasonal norms slightly below the 71-72°F September average. Only an undocumented station error or revised quality-control adjustment could alter the outcome, though such revisions remain rare for daily maxima once preliminary climatological reports are issued.