Winter Sports Reference Books

For in-depth information on specific winter activities, consider (all affiliate earnings donated):
The Avalanche Handbook 
Glacier Travel & Crevasse Rescue: Reading Glaciers, Team Travel, Crevasse Rescue Techniques, Routefinding, Expedition Skills 2nd Edition
Snowshoeing: From Novice to Master (Mountaineers Outdoor Expert)

Note these are all from the excellent Mountaineer Books series, the gold standard of outdoor books as far as I'm concerned. You can be sure they are written by experts.

Also from Mountaineer Books, the 2014 Backcountry Ski and Snowboard Routes - Washington for the best of the Washington backcountry. If you spend most of your time in Oregon, consider Backcountry Ski and Snowboard Routes: Oregon from 2011.