Official meteorological observations from Seattle-Tacoma International Airport and regional stations recorded a daily minimum of 54–55°F on September 16, 2026, under clear skies and light northeasterly winds that allowed efficient nocturnal radiational cooling. This aligns closely with the 1991–2020 climatological average low of 53.1°F for the date and reflects typical mid-September conditions without significant marine influence or cloud cover to moderate temperatures. Trader consensus at 100% implied probability for the 54–55°F bin stems from this verified data release, which matches National Weather Service preliminary climatological reports. Only major post-publication revisions or unresolved discrepancies among multiple reporting sites could realistically alter the outcome.