Recent National Weather Service and ensemble forecasts indicate a transition to onshore marine flow over western Washington by September 19, moderating temperatures after several days of offshore warming. Model consensus centers on partly cloudy skies with daytime highs near 70°F at Seattle-Tacoma International Airport, consistent with the late-September climatological average of 69–70°F. Key variables include the strength and timing of the marine push, which can suppress afternoon warming by several degrees, versus residual thermal trough effects that might allow brief clearing and readings in the low 72°F range. This narrow spread around 68–72°F underpins the closely matched market probabilities, with traders weighting the higher likelihood of marine moderation against the potential for slightly warmer interior conditions. Updated model runs and NWS briefings over the next 48 hours will refine these thresholds.