Recent National Weather Service and private model guidance for San Francisco shows a persistent marine layer with onshore flow and coastal stratus limiting daytime heating, keeping forecast highs clustered near 64–69°F for August 17. This pattern, typical of mid-August “Fogust” conditions, has produced below-normal readings in the low to mid-60s over the past several days, with only modest warming expected if the inversion weakens slightly. Traders have concentrated probability on the 68–69°F and 70–71°F bins because small differences in cloud cover timing, sea-breeze strength, and the depth of the marine layer can easily shift the daily maximum across those thresholds. Official NWS updates and real-time observations on the 17th will resolve the narrow spread.