**Clear skies, high pressure, and light northerly winds overnight into September 18 are favoring radiative cooling that should produce a low in the low-to-mid 50s Fahrenheit for Seattle.** National Weather Service forecasts and multiple private models consistently project a Friday low of 52–54°F under mostly clear to partly cloudy conditions, with onshore flow resuming and keeping temperatures seasonable rather than anomalously warm or cold. Recent days have featured sunny, dry weather with highs in the low-to-mid 70s and overnight lows already settling in the mid-50s, establishing a stable pattern with minimal frontal influence. Marine air from the Sound and light winds limit extreme cooling while preventing significant warming, aligning closely with mid-September climatology. The 54–55°F bin leads with 57% implied probability because it captures the consensus central tendency across official guidance, while adjacent 52–53°F and 56–57°F outcomes reflect minor model spread and typical forecast uncertainty ranges of a few degrees. No major shifts in the upper-level ridge or marine push are expected before resolution, supporting tight clustering around these values.