Trader sentiment for San Francisco's September 1 minimum temperature reflects high uncertainty around the typical mid-50s°F overnight low, driven by the weakening marine layer that moderates coastal conditions through cool, moist Pacific air and low stratus. Current National Weather Service guidance and ensemble models indicate partly cloudy skies with 55-57°F lows under persistent onshore flow, but variable marine layer depth, wind shifts, and radiative cooling under clearer skies could produce outliers below 50°F or above 65°F. Historical September averages near 56°F and the layer's seasonal decline support central bins, while model spread on inversion strength and any early high-pressure influence explains the balanced tail probabilities at 34.5%. Updated forecasts through the holiday weekend will refine resolution criteria.