This isn't the perfect situation for widespread valley snow, and the closer we get to Thursday morning the less impressed I am with the potential for heavy valley snow. The problem, as I see it, is the wind direction. Too much south wind, not enoough east or north wind. Yes, the pre-existing air mass is cold, Hillsboro has already been as low as 28°. But we can warm up rapidly when the south wind aloft gets going. I use the term "warm" a bit loosely here, I just mean warm enough so we get rain. Another wildcard is the precipitation rates. If it comes down really hard, there can be enough colling with the falling snow to lower the snow level and overcome any south wind warming. Bottom line is, south wind snow events are rare. Unless we get a good shot of offshore (east) winds, I think this is going to be more of a snow event for elevations just above the valley floor, with maybe an inch in the valley before it changes to rain.
KGW Chief Meteorologist