National Weather Service forecasts for San Francisco on August 21, 2026, indicate a high near 67–70°F under partly sunny skies, consistent with the long-term August average of 67–68°F at downtown and airport stations. Persistent onshore flow and a shallow marine layer—driven by the semi-permanent Pacific high—continue to advect cool, moist air from the ocean, suppressing inland heating and maintaining coastal stratus that limits daytime warming. Recent model runs show no significant offshore wind shift or subsidence that would allow temperatures to reach the low 70s, keeping the 68–69°F bracket as the market’s leading outcome at 44.5% implied probability while the 66–67°F and 70–71°F ranges capture residual uncertainty in exact marine-layer depth and timing of cloud clearance.