San Francisco’s marine climate, driven by the Pacific Ocean and persistent onshore flow, typically anchors overnight lows in the mid-to-upper 50s°F during late August as the marine layer deepens and limits radiative cooling. Current National Weather Service and model guidance indicate a low near 57–58°F tonight, with modest uncertainty tied to the precise depth and timing of stratus or fog that could allow brief clearing and slightly warmer minima or enhance cooling to the mid-50s. This consensus has concentrated the highest market-implied probabilities on the 56–57°F and adjacent 54–59°F buckets while assigning negligible odds to extremes below 52°F or above 60°F. No significant synoptic shifts or heat intrusions have altered the pattern in recent days, keeping trader focus on the next model runs and official observations from the primary reporting station.