Seattle’s July 24 high hinges on the interplay between onshore marine flow from the cool Pacific, the strength of the thermal trough, and any residual marine-layer stratus that can cap daytime warming. National Weather Service and model guidance currently place the most likely range near the climatological normal of roughly 78 °F, consistent with the near-even market probabilities clustered between 76–83 °F. Small shifts in wind direction or afternoon clearing can easily add or subtract 3–5 °F, keeping the distribution broad. Ensemble spreads from the latest GFS and ECMWF runs show modest uncertainty around these values, with no strong signal for either an extreme marine push or pronounced offshore warming expected before the daily maximum is recorded.