Persistent marine layer stratus and moderate onshore flow are the dominant factors keeping trader-implied odds clustered on 66–69°F for San Francisco’s August 13 high, with 66–67°F leading at 36%. National Weather Service guidance and ensemble runs indicate the inversion will limit daytime heating along the coast, consistent with typical August climatology where mean highs hover near 69–70°F but rarely exceed 73°F without offshore flow. Differentiation among the closely spaced bins hinges on subtle variations in marine-layer depth, stratus clearance timing, and any brief afternoon sunshine that could add 1–2°F; stronger or more persistent fog favors the lower outcomes, while partial burn-off supports the upper end. Updated model cycles and morning observations from the National Weather Service will provide the next resolution-relevant signals before the daily maximum is recorded.