Persistent marine layer conditions, currently deepened to 800–1,000 feet with lingering stratus per National Weather Service observations, are the main driver keeping San Francisco’s August 3 high temperature expectations clustered in the mid-70s. Onshore flow and a compressed inversion limit daytime warming despite seasonal peaks near 70°F climatology, with model consensus favoring 74–77°F outcomes that together hold over 54% market-implied probability. Subtle differences among leading bins hinge on exact marine-layer depth, sea-breeze timing, and 850 mb temperatures, which recent soundings show remain cool enough to cap highs below 80°F in most scenarios. Weak frontal influences noted in the latest forecast discussion introduce minor upside risk but are unlikely to overcome coastal cooling before resolution.