Recent National Weather Service guidance and model consensus indicate a persistent marine layer with morning stratus and moderate onshore flow will cap daytime heating in San Francisco on August 17, favoring highs in the upper 60s to low 70s. This aligns with the closely matched market-implied probabilities for 68–71 °F, reflecting trader assessment of typical August “Fogust” conditions where cool Pacific air and cloud cover suppress temperatures relative to inland areas. Differentiation between the leading bins hinges on variables such as the precise depth and timing of marine-layer clearing, sea-breeze strength, and any subtle warming from aloft; stronger or more persistent clouds tilt toward 68–69 °F while earlier dissipation or reduced onshore flow supports 70–71 °F. Historical climatology shows mid-August averages near 67–70 °F, providing context for the narrow range of plausible outcomes.