Persistent marine layer and moderate onshore flow from the Pacific are capping daytime heating in San Francisco, keeping official forecast highs centered on 69–71°F for August 12. National Weather Service guidance and ensemble runs highlight stratus and sea-breeze effects that delay warming until afternoon, aligning closely with the long-term August average near 70°F. These conditions explain why 70–71°F holds the strongest market-implied odds at 43 percent, followed by adjacent 68–69°F and 72–73°F bins, while warmer outcomes remain low-probability absent a notable weakening of the marine push. Traders are weighting the narrow spread between these bins against subtle variations in 925 mb temperatures and coastal wind strength expected in the final model updates before resolution.