Latest National Weather Service guidance and ensemble models indicate Seattle's August 19 high will likely fall in the mid-to-upper 70s, with marine layer and Puget Sound sea breezes limiting daytime warming under typical late-summer onshore flow. These factors create the tight clustering around 76–79°F, as modest differences in cloud cover timing or wind strength can shift the peak by a couple of degrees. The broader summer pattern of above-average warmth provides background support for the upper end of that range, yet short-range model spread and potential for afternoon marine stratus keep lower outcomes viable until final observations resolve the market.