Lowland snow is possible over northwest Washington from Saturday afternoon through Sunday. A low pressure wave will dive southeast through western Washington this weekend. North of the low track... cold air from the interior of British Columbia will spread into northwest Washington and cool the air mass enough for lowland snow. South of the low track... the atmosphere will be much warmer... with all rain expected. Enough precipitation could occur to bring signicant snowfall in the colder air.
The greatest uncertainty is where the rain-snow line will set up. There is moderate confidence that more northerly locations such as Whatcom County and the San Juan Islands will remain cold enough for snow throughout this event. There is moderate confidence that more southerly locations such as Grays Harbor... Lewis... Thurston and Pierce counties will remain warm enough for all rain. The greatest uncertainty and lowest confidence over precipitation type will lie in between... specifically for the north coast... Strait of Juan de Fuca... and the Puget Sound lowlands from King and Kitsap counties north through Skagit County. In these low confidence locations... this qualifies as a low-probability high-impact event.
Precipitation is most likely to arrive from the northwest on Saturday afternoon... then expand south through Saturday night. Heaviest precipitation is likely early Sunday morning. If the heaviest precipitation falls into adequately cold air... quite a few inches of snow would occur.
This potential lowland snow event bears watching. Plese check back for the latest updates on Friday and Saturday.