**Forecast models from sources like the GFS indicate a highest temperature in Seattle on October 1, 2026, most likely in the mid-60s°F, aligning with the climatological average high of 65.3°F.** Light northerly or variable winds, persistent morning cloud cover transitioning to partly sunny skies, and the moderating influence of Puget Sound are expected to limit strong daytime heating. The closely matched market probabilities for 66-67°F (32.5%) and 68-69°F (30.0%) versus 64-65°F (17.5%) reflect minor divergences across model runs on afternoon clearing and boundary-layer mixing. These small differences in solar insolation and advection under a stable early-autumn pattern create the primary uncertainty, with no significant synoptic shifts or marine intrusions indicated in the latest guidance.