Marine layer depth and onshore flow from the Pacific are the dominant drivers keeping San Francisco's August highs in the mid-to-upper 60s, with National Weather Service guidance showing a 66°F forecast high for August 15 amid persistent stratus and patchy drizzle that limit daytime heating. Recent cooling has placed temperatures well below seasonal normals, consistent with climatological August averages near 70°F at the airport but often lower in the city core due to the strong sea breeze and upwelling. Trader consensus clustering on 68-69°F (40.5% implied probability) reflects expectations for modest warming or clearing by afternoon, while lower bins capture the risk of a deeper marine layer suppressing readings to 66-67°F; higher outcomes above 70°F remain less likely without a stronger offshore component or model shift in the next 24 hours.