Uncertainty in overnight marine layer depth, cloud cover, and onshore flow strength from the Pacific is driving the tight probabilities for Seattle's August 24 minimum temperature, with 58-59°F and sub-50°F outcomes nearly tied. National Weather Service model guidance shows variable marine stratus influence that can suppress radiational cooling under clear skies or moderate temperatures when low clouds persist, producing forecast lows clustered in the mid-to-upper 50s against occasional cooler scenarios. This aligns with August climatology of 56-58°F average minima, where small shifts in wind direction or boundary layer moisture create the observed spread among 56-57°F, 58-59°F, and colder bins. Traders weigh the latest NWS and NOAA runs ahead of the resolution window, as any strengthening of the marine push could favor the lower tail.