The large ridge of high pressure that has been bringing warm and dry conditions to the West Coast is on timeout today as a large Pacific storm rolls onshore. Heavy rain, mountain snow, and gusty winds are all expected from this system as it moves east today.
Water Vapor satellite imagery (what’s that?) shows this system clearly off the Pacific Northwest coast. A plume of moisture is seen stretching from the tropical Pacific up to the Seattle area then east over the Northern Rockies. The speckled texture of the clouds off the Canadian coastline indicates an energetic system capable of heavy precipitation.
Heavy precipitation is exactly what’s in the forecast for these areas today, as seen by the Significant Weather forecast above. Dark green colors in the Portland Oregon area indicate heavy rain, with some hints that thunderstorms are possible as well. The dark blue colors in the Cascades west of Seattle indicate heavy snow, and the abundant nature of the moisture supply means that snow won’t stop in the Cascades. Moderate to heavy snow will continue all the way east into Montana today and tomorrow as the storm moves east.
Through tomorrow evening, a large amount of snow is expected to fall in the mountains of the Pacific Northwest. ECMWF liquid equivalent precipitation forecasts (what’s that?) show the higher summits receiving over 2″ of QPF (quantitative precipitation forecast) which translates to between 2 and 3 feet of snowfall accumulation. The passes are likely to see slightly lower QPF values, between 1 and 1.5″, which translates to 1-2 feet of snow. Use caution if you have to travel up through the passes in the next couple days, very slick winter driving conditions await. Heavy snow will also spread east into Montana, and the NW part of the state will likely pick up a couple feet of snow as this system rolls east. Several inches of rainfall can be expected in the lower elevations of Washington and Oregon, though it won’t bring nearly the same amount of impact as the snow.
Rain and snow will clear out tomorrow as colder and drier air moves into the region.