If I was the Mayor of Portland I would order some salt and be ready so spread it BEFORE any snow hits.
Portland Oregon Needs This
Here is the latest high resolution forecasts (and yes, there is still considerable uncertainty in the forecast).
To get snow and freezing rain, one needs cold air. That is coming, starting tomorrow. The following are a series of forecast maps from the UW high resolution prediction system, showing sea level pressure (solid lines) and temperature (shading, blue is cold).
4 PM Monday: mild (green color) air over most of the region.
On Thursday and early Friday an area of precipitation will move northward into the region (see the 24-h precipitation ending 4 AM Friday For most of the west, this will fall as rain, but in the Gorge and immediately downstream of it,there could be snow and freezing rain.