Recent National Weather Service and ensemble forecasts for San Francisco on September 30 point to a high near 76–77°F under building high pressure and reduced marine layer influence, supporting the market’s tight clustering around 74–81°F bins. Onshore westerly flow and potential patchy morning fog could cap readings in the mid-70s at coastal stations, while lighter winds and greater inland heating favor the upper 70s to low 80s; model spread in boundary-layer mixing and exact cloud cover accounts for the near-even odds between the leading 76–79°F outcomes. Historical September variability and the current warm anomaly above the 73°F seasonal average reinforce trader focus on these narrow thresholds ahead of the official daily maximum.