Trader consensus on the Seattle daily high for September 15 centers on the 64–67°F range, reflecting National Weather Service guidance of partly cloudy conditions with a forecast high near 69°F tempered by persistent marine-layer stratus and light northerly flow. These factors limit afternoon solar heating and promote modest mixing, keeping temperatures from exceeding the mid-60s in most ensemble members. Differentiation between the closely matched 64–65°F and 66–67°F bins hinges on the precise timing of any partial clearing and boundary-layer moisture; earlier sun exposure could add 2–3°F via enhanced sensible heat flux, while lingering drizzle or thicker clouds would cap the peak closer to 64°F. Historical September averages near 71°F underscore how the current onshore pattern has suppressed readings. Updated model runs and afternoon observations will refine resolution criteria ahead of market close.