National Weather Service forecasts and model guidance indicate a persistent marine layer and strong onshore flow from the cool California Current will cap San Francisco's high on August 31 near 62–66°F, well below the 69.6°F climatological average. Southwest winds of 10–20 mph and mostly cloudy skies are expected to limit afternoon warming, with the tight clustering of market probabilities around 64–67°F reflecting minor differences in model runs for stratus thinning and sea-breeze strength. Recent observations show this cooler regime has held through late August, and traders appear to be weighting the balance between slightly stronger marine influence (favoring the lower bins) and any temporary clearing that could push readings a degree or two higher.