The closely matched market-implied odds across the 70–77°F range reflect persistent uncertainty in the precise maximum for San Francisco on August 18, driven primarily by the depth and persistence of the marine layer. Official NWS and model guidance indicate a thick stratus deck and strong onshore flow off the cool Pacific, which typically caps afternoon highs near 68–72°F at downtown and airport locations by limiting solar heating and promoting advection of marine air. Recent observations show this layer extending 3,000–4,000 feet deep, suppressing warming consistent with climatological August averages around 67–70°F. Any thinning or delayed clearing could push readings into the mid-70s, while sustained fog and breezes favor the lower end; updated model runs tonight will clarify the timing of layer erosion ahead of tomorrow’s resolution.