Current forecast consensus from regional models points to a highest temperature in the mid-to-upper 60s°F for Seattle on September 21, driven by persistent onshore flow that sustains morning marine clouds before partial afternoon clearing under light northwesterly winds. This setup limits daytime heating relative to the prior day’s sunnier conditions, with official guidance from the National Weather Service highlighting highs near 66–68°F amid weak high pressure aloft. Trader positioning across the tightly clustered 64–69°F outcomes reflects uncertainty in exact peak timing, cloud persistence, and microclimate variations across the Puget Sound basin, where small shifts in insolation or wind could alter the daily maximum by a degree or two. Updated model runs and local observations in the next 24 hours will refine these probabilities.