The National Weather Service (NWS) - Seattle tweeted on February 9th:6.4" inch of snow at Sea-Tac yesterday. Seattle averages just under 6 inches of snow during the winter according to SeatteWeatherBlog.com. The weather set-up this week allowed for snow-supporting, cold air in Seattle (graphic below), but there is typically a competing factor that limits snow. In other words, winter weather in Seattle is regulated by its proximity to the Puget Sound and Pacific Ocean. Ironically, the snow cover itself amplifies the already cold temperatures.

Source: Forbes February 10, 2019 15:11 UTC