Recent National Weather Service guidance and ensemble model runs point to a Seattle high temperature near 78–82°F on August 20, reflecting persistent marine influence from the Puget Sound and Strait of Juan de Fuca that moderates afternoon warming. Onshore flow and variable low-level cloud cover create the narrow spread between the leading 80–81°F and 82–83°F bands, each carrying roughly 30% implied probability. Late-summer climatology around 77°F provides the baseline, while any reduced marine layer depth or brief clearing could nudge readings into the low 80s. Updated short-range model cycles and the next NWS forecast discussion will likely refine the exact maximum before market resolution.