When I was shooting a lot of winter sports, what we generally did was meter off the blue sky. It worked out well (the sky ends up being about the correct mid-tone). On an overcast day, meter off the snow and open up 1-1.5 stops. The other thing you can do is meter off the palm of your hand and open up a stop.
Peter Figen wrote:
One of the more difficult things to do is get the exposure perfect on color slide film in snow and direct sun. Nicely done.