Official observations from the National Weather Service at Seattle-Tacoma International Airport recorded a daily high of 66-67°F on September 21, 2026, under mild, partly cloudy conditions with light winds and no significant warming mechanisms such as downslope flow or clear-sky radiative heating. This aligns with climatological norms for late September, where average highs hover near 69°F, and recent model runs and surface analyses showed stable marine air influence suppressing temperatures below earlier forecasts. Trader consensus at near-100% probability reflects this verified measurement as the resolution criterion, with minimal scope for revision unless post-event data audits alter the official record.