Current National Weather Service and model guidance point to overnight lows near the long-term August average of 56°F for San Francisco on August 31, shaped by the persistent marine layer of cool, moist Pacific air advected onshore by the sea breeze. The California Current and coastal upwelling keep sea-surface temperatures in the mid-50s, limiting daytime heating and nocturnal radiational cooling under typical stratus and fog cover. Recent forecasts show partly to mostly cloudy conditions with light southwest winds, which can modulate the marine layer depth and produce small day-to-day variations in minimum temperature. With forecasts clustered around 55–57°F yet sensitive to subtle changes in wind, cloud cover, or inversion strength, trader probabilities remain dispersed across the 50s and low-60s ranges, reflecting genuine uncertainty in the final 48-hour model runs.