With a colder air mass over much of the Pacific Northwest, the biggest story this week will be temperatures, particularly in Western WA where they will be well below normal. This morning, a cold front was located across Western OR, extending south-southeastward into northern Nevada. The region is under the influence of cold high pressure, centered well to the north over northern British Columbia and an accompanying upper-level ridge of high pressure just off the West Coast.
Over the next several days, weather should remain quiet over the region with the ridge progressing eastward this week. The surface high will shift southeastward towards the the Canadian Prairies and Great Plains. This will open up an opportunity for rain and snow by Saturday. In the meantime, highs will only top out in the mid-30s in Seattle this week, under the influence of cold northeast winds. Portland will be even colder (around 30) with easterly winds blowing cold air from Eastern WA through the Columbia River Gorge into the area. And of course, much of Eastern Washington will be quite cold with highs in teens in the Spokane area and much farther south into southeast Oregon, highs in the 20s. On Friday and Saturday, snow levels will be very low (near the surface to 500ft) prompting the possibility of lowland snowfall. Much will depend on geography, as it many times does in snow situations in the Pacific Northwest. Areas which funnel colder air into valley areas such as the Fraser River Valley and Columbia River Gorge or areas which pool colder air such as the Hood Canal area are more likely to see good snowfall in a marginally cold air set up. It will interesting to see the exact details later this week.
Current Watches/Warnings/Advisories (as of this post)
Wind Chill Warning for part of Eastern Washington
Frost Advisory for the south Oregon Coast
Frost Watch for the south Oregon Coast