Trader sentiment for Seattle's August 17 high temperature centers on the 78-79°F bin as the modal outcome because long-range ensemble guidance and climatological baselines for mid-August place typical highs near 77-79°F during an ongoing warmer-than-average summer. Key variables include the strength and position of the marine layer, which can suppress or enhance afternoon warming; steering flow from the Pacific that modulates onshore advection; and model spread in cloud cover or subsidence that determines whether peaks reach the low 80s or stay capped in the mid-70s. Recent NOAA outlooks reinforce elevated odds for above-normal warmth across the Pacific Northwest without signaling an extreme heat event, keeping lower bins under 10% and higher bins (82°F+) thinly traded. Resolution hinges on official National Weather Service observations at Sea-Tac Airport.