Forecast uncertainty for San Francisco’s overnight low on August 24 stems primarily from variable marine layer depth and onshore flow strength, with National Weather Service and ensemble models showing a spread of roughly 52–62 °F. The marine stratus and fog that typically moderate coastal temperatures this time of year can either thicken to produce readings near 55 °F or remain shallow under stronger high pressure, allowing lows closer to 60 °F or briefly above. Recent upper-level ridging has kept the layer thinner than normal, boosting probabilities for the 58–59 °F bin while still leaving room for cooler advection if a coastal eddy develops overnight. Historical August climatology places the median low near 55–57 °F, yet day-to-day model runs have shifted several degrees in the past 48 hours, explaining why no single outcome exceeds 40 % implied probability and why traders are closely watching the next 00Z and 12Z model cycles for boundary-layer moisture and wind shifts.