It's a challenging time of year to visit, but it can still be interesting. In Oregon, the east side of the Cascades is much drier and often is clear when the Willamette Valley is socked in. But it's colder, and most campgrounds are closed. To cross the mountain passes you may well need snow tires or chains, if a storm comes through. But if you are up for it, the snow-covered mountains are spectacular. The west side of the Cascades are much less likely to have snow, but it may well be rainy with foggy mornings. The coast can be very interesting under these conditions, if the wind is not up--actually warmer than farther inland. And if you like rain forests--well, you will be seeing them in under their most typical, namesake conditions.