**Marine layer depth and onshore flow are the dominant factors shaping trader consensus around a 66-67°F high for San Francisco on August 13.** Official National Weather Service and AccuWeather guidance point to a persistent marine layer keeping coastal areas under clouds or overcast skies, limiting daytime heating to the mid-to-upper 60s at KSFO and downtown stations. This aligns closely with the market-implied odds, where 66-67°F leads at 36.5% and 68-69°F follows at 27.5%, reflecting modest uncertainty in exact clearing timing or layer thickness. Recent model runs show a cooling trend through mid-August, with sea breezes strengthening and preventing significant inland warmth from reaching the immediate coast. Historical August averages near 69°F provide context, but current conditions favor the lower end of the normal range due to enhanced onshore flow and possible light drizzle overnight. Traders appear to weigh these dynamics against slight model spread on afternoon sun exposure, which could nudge readings into the upper 60s if the layer thins earlier than expected. No major synoptic shifts are anticipated before resolution, keeping focus on the 64-69°F band where most probability is concentrated.