Snow will move into the Cascades and BC midweek. That system should land some double digit totals by Thursday or Friday before moving into the Northern Rockies late this week or the weekend.
Model confidence is high that moisture and generally cool conditions will move into the Cascades and BC by midweek. The GFS pushes higher amounts into a wide area of BC, and most of the WA Cascades by Wednesday or Thursday. Some snow may also be falling into the Oregon Cascades albeit lower amounts. The Euro is a bit slower and shows the highest amounts falling further north. It's likely that Whistler land some moderate to heavy snow by late this week with decent confidence for the northern Cascades of Washington (Mount Baker). Moderate confidence exists for decent snowfall for the central and southern Cascades (Stevens and Crystal). Remember, the GFS is pretty bullish for some pretty hefty amounts above 5500 feet this week. The Euro is a bit more pessimistic for the central and southern areas of Washington and still bullish up north. Snow levels hover between 4K to 4500 midweek with some slight cooling in the latter half. Some spots in the PNW are going to end up with some pretty hefty amounts by late this week.
Below: Total snowfall through Friday night for Washington State. The GFS shown here is very bullish for many areas above 5500 feet. Some wet snow may also be falling at times at the bases. The Euro is less bullish for totals not shown here. Confidence will be narrowed in with a later forecast. Whistler is also well within range of seeing some heavy snow at upper elevations this week.
Below: Midweek trough entering the Pacific Northwest and Coastal BC Wednesday/Thursday.
The Pacific Northwest trough will weaken as it moves inland. That system appears to focus on the Northern Rockies (North-central Idaho, Montana) before dropping south, perhaps over the Tetons and much of Colorado by the weekend. The models are not in agreement on strength. Some point to a decent dump for areas further north once again in Montana with less to the south. It's likely that many areas of the Montana, the Tetons and Colorado will see some snowfall by Saturday or Sunday this week. Stay tuned to the forecast as I update storm totals for the extended period. Beyond the 7 day period, a trend for high pressure is likely to take hold on the west (Week #2).