Recent National Weather Service and model guidance for San Francisco on September 13 point to a typical late-summer marine layer with onshore westerly flow holding daytime highs near the 1991–2020 climatological average of 70.8°F. Multiple forecasts converge on 68–72°F under mostly sunny skies and breezy conditions, aligning with the market’s heavy weighting toward the 70–71°F bin. A brief early-September heat spell peaked at 94°F on the 9th but has since moderated, reducing upside risk. Traders appear to discount higher outliers given persistent northwest winds and the low probability of offshore flow or clear-sky amplification before resolution. Updated model runs and official NWS briefings tomorrow morning represent the next key data points likely to refine these implied probabilities.