From Portland National Weather Service
A cold front drops south from Alaska this weekend with a cold air mass pushing into the region. Cold air filters into SW Washington and Oregon beginning late Saturday then settles in place by Sunday. Additionally, moisture moves into the region at the same time in the form of showers. With the cold air already over the region. Snow showers are likely across the area.
Snow accumulations of a few inches are possible from elevations of 500 to 1000 feet and above. Though in a showery air mass accumulation of snow can vary significantly. Snow showers will reach the valley floor at time and in heavier showers snow may accumulate briefly.
A change in the weather pattern can be expected again by midweek with a potentially warmer and wetter pattern moving in, though details are uncertain at this time.