National Weather Service guidance and ensemble models indicate a daily maximum near 77–79°F for Seattle on August 11, shaped by a moderating marine layer and onshore flow that caps daytime heating after morning cloud cover. This aligns with August climatology at Sea-Tac, where the median high is about 76°F, though 2026’s broader summer warmth has kept conditions modestly above normal. Traders assign the highest implied probability (44.5%) to 78–79°F because recent model runs show limited potential for stronger ridging or offshore flow that could push readings into the low 80s, while the chance of cooler marine influence keeps lower bins like 76–77°F in play at 18.5%. Updated forecasts ahead of the 24-hour window will determine final resolution.