**Persistent marine layer influence from the cold California Current and coastal upwelling is anchoring San Francisco temperatures near the mid-to-upper 60s on August 28.** Official NWS forecasts and recent observations show mostly cloudy conditions with highs expected in the mid-60s, consistent with the 66–69°F range holding the largest share of market-implied probability. The layer’s depth and the strength of onshore flow—driven by the inland thermal low—limit afternoon solar heating and keep the city well below seasonal averages near 70°F. Differentiation among the closely matched 66–69°F, 70–71°F, and 64–65°F buckets hinges on the exact timing and extent of any marine-layer thinning or partial clearing, along with wind speeds that could allow modest warming or reinforce cooling. No unusual large-scale pattern has emerged to push outcomes outside this narrow band.