Winter, like other seasons, should be enjoyed to its fullest.
My suggestion is to create a snowball game, team versus team style with fortifications and other cool stuff. Then hold annual snowball fight competition with prizes every year.
Few additional suggestions:
no potions or magic can be used and all participants should wear the same snowball game grab instead of armor to make it more fun.
to strike out an opponent he should be hit with a snowball certain number of times this way game would not depend on pcs HP.
Japanise Yukigassen tournament is super fun, we could have something similar :)