**Marine layer persistence and westerly onshore flow are anchoring San Francisco's overnight minimum near 58–61°F for August 27, aligning with the market's top-implied outcomes (60–61°F at 42.5%, 58–59°F at 31.5%).** National Weather Service and local model guidance indicate a shallow marine layer will maintain stratus and moderate radiational cooling overnight, with lows forecast in the upper 50s to low 60s under mostly cloudy to partly cloudy skies and west-southwest winds of 10–20 mph. This reflects typical late-August climatology (historical average low ~56°F) tempered by recent ridge-trough balance that has kept coastal temperatures near or slightly below seasonal norms without strong offshore warming. Recent observations show consistent 58–60°F minima amid fog and haze, with no significant heat intrusion or clear-sky radiative cooling expected to push readings notably lower or higher. Model consensus and the approaching trough (bringing cooler air Friday onward) reinforce the narrow probability band around these values, while lower-probability tails (<55°F or >63°F) remain limited by the stable marine influence.