Forecast models from the National Weather Service and supporting agencies indicate a low near 50–55°F for Seattle on September 29 under persistent cloud cover, light rain, and southerly winds of 10–20 mph. These conditions limit nighttime radiative cooling and support the market’s leading 54–55°F bin at 63% implied probability. Historical September averages place the daily low around 50°F, with recent late-month observations ranging from the mid-40s to mid-50s depending on cloud timing. The 29% probability assigned to 47°F or below reflects residual uncertainty in exact clearing timing or localized cooling pockets, while narrower bins around 50–53°F capture secondary model outcomes. Updated NWS guidance and hourly observations through the overnight period will determine final resolution.