Incoming low-pressure system tracking onshore Thursday evening will deliver widespread rain, cloud cover, and cooler marine air to the Pacific Northwest on September 25, suppressing daytime highs and limiting overnight radiational cooling. National Weather Service guidance and ensemble runs show Seattle overnight lows centered near 50–52 °F, with some model solutions dipping into the mid-40s under heavier rainfall and others holding above 52 °F if breaks in cloud cover allow modest warming. This narrow spread around the climatological early-autumn minimum produces closely matched market-implied probabilities across the 45–53 °F bins, as traders weigh the system’s exact track, rainfall totals, and boundary-layer mixing against historical September low-temperature distributions. Updated model runs and NWS forecast discussions expected through Thursday will provide the next clearest signals on whether the minimum settles in the upper or lower half of that range.