Right now the running team that I coach is several weeks into training for their spring marathons and half marathons. Lots of them are planning ski weekends for President's Day weekends, and they're wondering how a weekend of skiing will affect their training schedule. Should they still do a long run that weekend? Or is a weekend of skiing enough activity for one weekend?
First of all, skiing, especially cross-country, or even snowboarding, can be excellent cross-training for running and is a great way to supplement your training for a half or full marathon. If you're training for one of those long distance events, you also know the importance of doing your long runs once a week and gradually building up your mileage. Of course, it can be beneficial (both physically and mentally) to have one "rest" weekend a month, where you either go down in mileage for your long run or do cross-training instead of running. So, many half-marathoners-in-training and marathoners-in-training can go away for a weekend of skiing and use it as a "down" week in mileage. However, if you're a little behind in your training, you may not be able to afford to miss a long run and may have to squeeze in a long run before you leave for your trip.
And if you're going to be away for a whole week of skiing, it's a good idea to try to do at least one or two shorter runs on a treadmill while you're away. Although you'll be active during the week, it's important to keep your body and mind focused on the event that you're training for.