Recent National Weather Service forecasts indicate a high near 73°F (23°C) for San Francisco on September 24 under mostly sunny conditions following patchy morning fog, consistent with trader consensus clustering in the 70–75°F bins. The primary driver is the seasonal weakening of the marine layer—a cool, moist boundary layer over the cold California Current—as the North Pacific High shifts and the Central Valley thermal low moderates, reducing onshore advection of marine air and allowing greater daytime solar heating. Key differentiating factors include the precise depth and timing of any residual stratus or inversion, which can suppress highs by several degrees if persistent, versus light westerly winds that enhance mixing and push temperatures toward the upper 70s. Ensemble model spread and San Francisco’s sharp microclimate gradients introduce uncertainty, with new guidance expected to refine the exact peak before resolution.