**A stable weather pattern featuring a persistent marine layer and moderate onshore flow is anchoring trader expectations for San Francisco’s August 20 high temperature near the upper 60s to low 70s.** Official National Weather Service and extended forecasts point to a 66°F high under overcast skies, with recent days registering 66–69°F amid a deeper-than-normal marine layer that has produced coastal stratus, limited afternoon clearing, and occasional drizzle. This layer—often 2,000–4,000 feet thick—suppresses daytime heating by reflecting sunlight and advecting cool Pacific air via prevailing westerlies. The market’s tight clustering around 68–71°F reflects both climatological norms (August averages near 67–70°F) and uncertainty over whether the marine layer will burn off earlier than modeled or if a weak upper-level ridge will allow brief warming. Key variables include marine-layer depth and burn-off timing, wind speed (stronger onshore flow keeps readings lower), cloud cover fraction, and any subtle shifts in the eastern Pacific low or Four Corners high that could alter subsidence. With forecasts holding in the mid-to-upper 60s and no major heat-wave signal, the distribution favors outcomes near the historical August range while leaving room for modest upside if skies clear more than expected.