Current National Weather Service guidance and short-range model consensus favor a San Francisco high near 68–70°F on August 21, with the marine layer and moderate onshore flow suppressing afternoon warming under persistent stratus and sea breezes. Typical August climatology at San Francisco International Airport shows a normal maximum around 73°F, yet recent observations indicate cooler outcomes remain plausible if fog lingers or winds strengthen, while partial clearing could allow brief warming into the low 70s if the inversion weakens. Trader-implied probabilities cluster tightly around the 68–71°F bins because small differences in cloud timing, wind speed, and boundary-layer mixing can shift the daily peak by a degree or two. No anomalous heat signals have emerged to alter this range.