Trader consensus clustering around 72–75°F for San Francisco’s August 5 high reflects the persistent influence of the marine layer, a shallow, cool, moist air mass formed by the strong temperature contrast between the cold California Current and warmer inland air. Onshore westerly flow and a temperature inversion limit daytime mixing and solar heating, keeping coastal maxima well below inland values amid the broader heat pattern. Subtle differences among the leading bins hinge on marine-layer depth, the strength of the sea breeze, and any midday erosion from high pressure aloft—variables that National Weather Service and NOAA model runs continue to refine. Historical August climatology at KSFO shows typical highs near 70°F with only modest day-to-day variability, underscoring why traders assign low probability to extremes above 78°F. Updated short-range guidance expected later today could shift odds if inversion strength or wind forecasts change.