**Forecast uncertainty around marine layer strength and wind patterns is the main driver behind the closely matched leading bins for San Francisco’s October 4 high.** Official NWS guidance and ensemble models show highs centered in the mid-70s to low-80s, with SFO-area forecasts ranging 80–84 °F amid partly cloudy conditions and light northwest flow. Offshore or downslope winds could briefly enhance warming and push readings toward 86–87 °F, while a stronger or more persistent marine layer would cap temperatures near 82–83 °F. Historical October variability and the two-day lead time keep probabilities distributed across the 78–89 °F range rather than concentrating on any single outcome.