Seattle's forecast for August 21 centers on a mild summer pattern typical of the region, with official National Weather Service guidance and model consensus pointing to afternoon highs near 80°F under partly sunny skies and light onshore flow from the Pacific. This keeps temperatures moderated by the marine layer and Puget Sound influence, though any temporary offshore winds or reduced cloud cover could nudge readings into the low 80s at Sea-Tac Airport, the likely measurement site. Ensemble spreads from global models show tight clustering in the 78–83°F range, reflecting normal short-term uncertainty from diurnal heating and boundary-layer mixing rather than major synoptic shifts. Historical August averages near 76–79°F provide context, while 2026's above-normal seasonal trend supports the market's concentration on 80–83°F bins as the most probable outcomes.