The wintery weather will stick around on Monday for western Washington and northern Idaho. Snow will also make way into the Bitterroots of Montana, and a few showers will sneak into northwestern Oregon.
On Tuesday, the weather will be the most active, with widespread rain and elevation snow. The reason for this is a direct tap of moisture from Hawaii. There will be a narrow plume of moisture originating from the central Pacific that will make its way into the Pacific Northwest due to steering winds. Rain will start in western Washington, but will spread into western Oregon as the day progresses. Snow will also come down in the Cascades, bringing heavy accumulations, up tp several feet in total from Sunday through Wednesday. Overnight Tuesday, the storm will strengthen. Snow will continue to crank in the Washington Cascades as well as the Oregon Cascades. Rain showers will move into eastern Washington and the valleys in northern Idaho.
Wednesday will be a big event for northern California, where rain is desperately needed. Showers will potentially make it as far south as the Bay Area. North of there will see widespread rain, and there will be heavy snow in the the northern and central Sierra as well as the northern coast ranges. A few rain showers may sneak into the central valley of California, but this will likely be very spotty. Snow will also move into much of Nevada, Montana, Idaho, western Wyoming, and northern Utah. Most of the activity will wind down in Washington and Oregon on Wednesday, although a light snow is still possible in the Oregon Cascades.
Later on in the week, this storm will strengthen further, bringing snow to all of the Rockies. This will then turn into an even larger system, affecting most of the remainder of the nation through the weekend.