Recent National Weather Service and model guidance indicate mostly clear skies and light southerly winds overnight into September 18, supporting overnight lows in the low to mid-50s Fahrenheit across the Seattle area. This pattern stems from persistent high pressure and minimal cloud cover, which limits radiational cooling while keeping temperatures above seasonal norms for mid-September. Trader sentiment clusters around the 52–55°F bins because ensemble forecasts show modest spread from slight variations in boundary-layer moisture and wind speeds. New NWS model runs and any late-day frontal approach could shift the minimum by a degree or two before the official observation at Sea-Tac or downtown stations resolves the market.