Latest National Weather Service guidance and ensemble model runs indicate modest overnight cooling for San Francisco on August 30 amid variable marine layer depth and light onshore flow, keeping the lowest temperature clustered near 56–59 °F and driving tight market-implied odds across the leading bins. Persistent coastal upwelling from the California Current maintains ocean surface temperatures near 55 °F, while the marine layer’s stratus clouds limit radiational cooling yet sustain cool, moist boundary-layer conditions typical of late August. Minor differences in inversion height, wind mixing, and cloud timing among GFS and ECMWF solutions account for the narrow spread separating 54–55 °F from 58–59 °F outcomes, with historical climatology showing mid-50s lows as the norm before the seasonal marine-layer retreat begins.