Recent National Weather Service guidance and ensemble models indicate Seattle's August 22 high will likely peak near 70-72°F as an upper-level low approaches from the southwest, advecting cooler marine air and increasing cloud cover with a 30-40% chance of showers or drizzle. This suppresses daytime heating relative to the 76°F climatological average, while southerly winds around 5-10 mph limit mixing. Minor model spread on timing and coverage of precipitation creates the tight market clustering between 70-71°F and 72-73°F bins, with traders weighting official forecasts and recent runs showing temperatures tracking below seasonal norms. Updated model guidance and local observations through Friday evening will refine the exact maximum before resolution.