Traders see 52-53°F and 54-55°F as the leading outcomes for Seattle’s minimum temperature on September 19 because short-range model guidance shows a moderating marine air mass arriving with light winds and increasing cloud cover. These conditions reduce radiational cooling overnight while keeping dew points in the mid-40s, limiting how far temperatures can drop below the seasonal average of roughly 53°F. Minor differences among National Weather Service and Global Forecast System runs center on exact cloud timing and boundary-layer mixing, which can shift the low by 1–2 degrees. Updated model cycles and local observations over the next 48 hours will likely narrow the range before the daily minimum is recorded.