A pocket of cold air moving southeast from the Gulf of Alaska toward the Pacific Northwest will cause snow levels in the mountains to plunge overnight in the Olympics and north and central Cascade mountains.
The snow level Friday is at 9,000 feet. KIRO 7 meteorologist Morgan Palmer said that level would fall to 3,000 feet by Saturday morning.
The National Weather Service issued a winter storm watch from 11 p.m. Friday to 5 p.m. Saturday for areas above 3,000 feet with 4 to 8 inches of snow accumulation.
Palmer said Snoqualmie Pass will likely see snow accumulations in the lower end of that range.
Palmer said snow will begin falling at Stevens Pass at 4,000 feet no later than 4 a.m. Saturday, while Snoqualmie Pass may not see snow until between 6 a.m. and 8 a.m.
Both locations will see an earlier onset of snow if a convergence zone forms, dragging colder air down and consequently dropping the snow level.
The phenomenon, if it forms, will be likely to enhance snow and speed up the switch from rain to snow at Stevens Pass.
Through the day Saturday, expect chilly showers in the lowlands with highs barely reaching 50 in Seattle with snow showers above 3,000 feet continuing.
Snow amounts by the day’s end will be in the range of 3 to 8 inches in the mountains, with higher amounts generally occurring at higher elevations.
From Sunday into next week, cold lowland rain and light mountain snow will continue.