Official forecasts from the National Weather Service place San Francisco’s August 12 high near 69–72 °F, aligning with the market’s near-even split between the 68–69 °F and 70–71 °F bins. Persistent onshore flow and a strong marine layer typical of mid-August keep coastal maxima close to seasonal normals of ~70 °F, limiting afternoon warming despite clear skies after morning clouds. Minor model differences in marine-layer depth and wind timing create the tight probability spread, with any late-day clearing or stronger westerlies able to push readings into the low 70s or hold them in the upper 60s. Traders are effectively pricing the narrow uncertainty band around the official guidance ahead of tomorrow’s official observation.