Recent National Weather Service guidance points to a San Francisco high near 70°F on August 24, underpinning the market’s leading 70-71°F outcome at 31% implied probability. Persistent marine layer stratus and moderate onshore flow off the cool Pacific are limiting daytime heating, a classic late-summer pattern reinforced by coastal upwelling. Ensemble forecasts show only modest diurnal rises, with any clearing dependent on the strength of the onshore gradient. Traders are weighting the narrow 68-72°F band most heavily because small shifts in fog timing or wind speed can swing the maximum across the tightly clustered bins.