Current National Weather Service forecasts for San Francisco on September 30 point to a high near 70°F under mostly clear skies and light westerly onshore flow, driven by a strengthening marine layer and modest ridging aloft following a recent upper-level trough. This setup favors the 73°F-or-below outcome as the modal range, consistent with climatological September highs averaging 71°F and typical coastal suppression from Pacific waters. Key variables differentiating adjacent buckets include marine-layer depth and inversion strength, which control how much afternoon mixing occurs, plus any shifts in the pressure gradient that could enhance or weaken the seabreeze. New model runs and NWS updates over the next 48 hours will refine these details ahead of market resolution.