Current forecasts for San Francisco on August 17 center on a persistent deep marine layer exceeding 2,000–4,000 feet, which limits daytime heating through enhanced onshore flow and coastal stratus, keeping highs most likely in the 68–71°F range. National Weather Service model consensus and recent soundings show this pattern producing below-normal temperatures amid variable fog and possible drizzle, with only modest warming expected if the layer thins briefly. Trader probabilities reflect this narrow band of uncertainty between adjacent bins, as small shifts in wind strength or inversion height could tip the daily maximum across the 70°F threshold while historical August averages near 67–70°F provide context for the tight distribution.