Recent National Weather Service and model guidance indicate a high near 69–71°F for San Francisco on September 11, following a sharp cooldown from the prior day’s record warmth as onshore southwest flow strengthens and a marine layer develops. This setup favors morning clouds that limit afternoon heating, with sea-surface temperatures and the typical September pressure gradient keeping maxima close to the 70.6°F climatological normal. Trader emphasis on the 70–73°F bins reflects uncertainty in exact marine-layer depth and wind timing, both of which can shift the peak by 1–3°F; lighter winds or delayed clearing would push readings toward 72–73°F, while stronger onshore flow or earlier fog would cap them at 70–71°F. Updated model runs and the afternoon forecast discussion will provide the next key data point for resolution.