Lots of good ideas!
I don't live in a place that struggles with ice/snow either (California) but we do get A LOT of rain in the winter which makes our outdoor arenas muddy and unridable.
We ride on the road (not the pavement, I mean the dirt roads around the barn).
Its almost like we make our own little tracks around. You have to be careful, make sure you use wraps or splint boots because it still can be slick. Lunging on the road if riding is just not possible is good too.
If all else fails, hand walking and trotting just so they get exercise is a good option... think of it this way: You could get a lot of ground work done!!! Lol Horses can always improve on ground manners no matter how old they are!!!
I don't know when the snow comes up there, but ride as much as you can before!!!
All the best,