All of this is based on my own personal experience of walking in the snow, on something I read once that claimed many medieval European villages more or less shut down and hibernated in the winter, and on the knowledge that military campaigns pretty much took the winter off back in the day. What I am really looking for, however, are specifics. How did people actually get around in the winter during the High Middle Ages (1000-1300)? Sledges? Nordic skiing? Was there any kind of system for keeping roads clear of snow? How deep does snow have to get before traveling on horseback, or by horse-drawn sleigh, is impractical?
I've done a lot of googling ("medieval winter travel," "winter travel middle ages," "winter horseback riding," "history of Nordic skiing," etc). Found some fun and interesting stuff, including an article about what it would take for Robin-Hood-esque outlaws to survive Sherwood Forest in the winter, but nothing about the large-scale effects of winter on medieval infrastructure in northern Europe.
Any help or personal anecdotes would be appreciated!