Recent National Weather Service and ensemble model guidance points to a Seattle minimum on September 19 in the low-to-mid 50s under partly cloudy skies, light winds, and dew points near 52°F that will moderate radiative cooling. Persistent high pressure and marine air from Puget Sound have produced similar overnight lows the past several nights, with historical September averages around 52–53°F providing climatological context. Slight differences among forecast runs—particularly in cloud cover timing and boundary-layer mixing—create the narrow spread across the 50–55°F bins that currently dominate trader positioning, while lower-probability tails reflect the small chance of clearer skies or stronger onshore flow pushing readings outside that range before official observations close the market.