**Marine layer persistence and onshore flow are the dominant factors keeping San Francisco’s maximum temperature on August 27 clustered near 72–75 °F, which explains the tight market spread between the 72–73 °F (25.5 %) and 74–75 °F (26.5 %) bins.** National Weather Service guidance issued August 26 projects partly cloudy skies with a daytime high of 73 °F for the San Francisco area and 76 °F at the airport, reflecting modest warming from a high-pressure ridge extending from the Southwest. Coastal stations remain cooler than inland valleys because persistent northwest winds and the marine layer limit daytime heating; typical August afternoon maxima at official sites average 68–72 °F. Minor model differences in marine-layer depth, wind timing, and cloud clearance create realistic scenarios for a peak in the low-to-mid 70s versus the upper 70s, sustaining the near-even implied probabilities. A cooldown signal appears Friday, but tomorrow’s outcome hinges on the precise evolution of the onshore flow through the afternoon peak-heating window.