The National Weather Service's official climatological summary for Seattle-Tacoma International Airport recorded a daily maximum of 69°F on September 18, 2026, driving the market's unanimous 100% consensus on the 68-69°F outcome. Onshore flow produced morning low clouds followed by afternoon clearing, limiting highs to the upper 60s to low 70s and aligning with the month's cooling trend that has featured zero 80°F days. This reading sits slightly below the 1991-2020 normal high near 70-71°F for the date and matches model consensus emphasizing persistent marine influence rather than warmer downslope or offshore patterns. Official verification from the primary reporting station leaves little scope for revision, though any post-analysis adjustment to the exact peak timing or station reading could theoretically shift resolution.