Marine layer influence and persistent onshore flow from the Pacific are anchoring San Francisco’s overnight minimum near the historical 56°F average for September 3, with current model guidance and station observations centering the daily low between 58–61°F. Coastal stratus and light drizzle have moderated radiative cooling overnight, while variable wind speeds of 5–15 mph prevent sharper drops. Traders assign roughly equal implied probability to the 60–61°F and 58–59°F bins because small differences in marine layer depth or timing of clearing can shift the recorded minimum by 1–2°F across official stations. Updated National Weather Service guidance and hourly observations through dawn remain the key near-term catalysts.