It's tough to get snow on the valley floor without an east or north wind, but it does occasionally happen. This will be one of those occasions. Substantial snow will stay bottled up at elevations above 500 feet, but flakes are likely to fall all the way down to sea level. From sea level to about 500 feet, the only chance for sticking snow will come in bursts of heavy showers. Why? Because the precipitation rates in these showers are high enough to help cool the air column enough to allow snow to reach sea level. There can also be downward bursts of colder air from the snow showers that bring flakes to the valley floor. But usually after one of these "snow bursts" the snow on the ground melts away as temperatures rebound after the snow shower passes.
As you go up in elevation, the snow amounts will increase dramatically:
1-2" from 500 to 1,000 feet
2-4" from 1,000 to 2,000 feet
3-8" from 2,000 to 4,000 feet
15-25" above 4,000 feet
Which means a great day of powder skiing on Mt Hood and across the Cascades. As the air turns colder the snow becomes lighter and fluffier. Whenever the snow level is flirting with the valley floor, it usually means great powder on Mt Hood.
Meanwhile, back in the valleys, the silver lining to this forecast is we finally should get some sun. Clouds will begin to clear Wednesday afternoon, and although there will be lingering snow flurries Thursday we should see increasing clearing. East winds will kick in as another batch of cold air descends from Canada to eastern Washington and Oregon. The next storm, which is weak, looks at this point to drop southward along the coast and miss Oregon as it moves into California. If this system comes closer, then we'll see some snow, probably light, on Saturday. But at this point, New Years Day looks clear, cold and windy in the Portland area. Monday brings a transition back to warmer weather as a new storm approaches form the west. As usual, this can mean more snow before it warms up enough to mix back to rain. Stay tuned on that one!
KGW Chief Meteorologist