Recent National Weather Service and ensemble model guidance for Seattle on August 18 centers on a high near 76–79 °F, reflecting typical mid-August climatology under a modest ridge with light onshore flow moderating temperatures. Trader consensus in the 76–77 °F and 78–79 °F bins arises from small differences in forecast timing of marine-layer influence and afternoon cloud cover, which can suppress or allow a few extra degrees of warming relative to the 77 °F seasonal average. A warmer-than-average summer baseline supports the modest upside skew toward the upper 70s, while any earlier-than-expected onshore push or increased marine stratus would favor the lower side. Updated model runs and afternoon observations on the 18th will refine resolution criteria for the daily maximum at official stations.