If you can tolerate rain, the pac northwest hardly ever gets cold when compared to other cities. It's been a fairly dry summer thus far. Portland should of already had about 19 inches of rain, we're hovering around 13, way below average. I'd say late Feb through the first week of November it's riding weather. Three months out the year you can still ride but it's wet and a little cold but temps hover around high 30's, low 40's.