**Official National Weather Service observations confirm the Seattle-Tacoma International Airport recorded a minimum of 54°F on September 9, 2026, matching the market's dominant 54-55°F outcome at 96.5% implied probability.** This value fell just 1°F below the 1991-2020 climatological normal of 55°F amid stable high-pressure conditions, clear skies, and light northerly winds that supported typical nocturnal radiative cooling without anomalous cold-air advection or cloud cover to moderate temperatures. Recent model consensus and surface observations aligned closely with this range, reflecting low forecast uncertainty in the late-summer regime. Unlikely challengers include station-specific microclimate differences or post-event data revisions, though the official airport reading serves as the primary resolution source.