**Persistent marine layer and a deepening upper-level trough off the West Coast are keeping San Francisco’s overnight lows near or slightly below the early-September average of ~56°F.** Official guidance shows partly to mostly cloudy conditions on September 2 with southwest winds and possible drizzle, limiting radiational cooling while onshore flow maintains marine air. Model consensus points to a minimum in the mid- to upper-50s, but small variations in marine-layer depth, cloud timing, or wind strength can shift the exact low by a degree or two. With all outcome bins trading near 48–50% implied probability, traders are pricing in genuine forecast uncertainty around the narrow historical range for the date. New model runs and updated National Weather Service briefings over the next 48 hours will provide the clearest signals for resolution.