Central Alberta here, 6 months of snow and cold :)
My boys live out 24/7/365. They are unshod and unrugged and not clipped. The snow here is deep (and crisp and even). I worry only when there has been a spring melt followed by a spring freeze - but regardless of my worry my boys manage just fine and they are adept at judging what is deep snow, and what is icy. Plenty of hay, and a water heater in their trough.
I was in the UK, where a snowy week can be far more deadly because it's more like sheets of ice than proper deep snow. In those conditions the horses stayed indoors because the yard and their fields were treacherous.
If your three months of snow are consistently cold, then your horses will be fine. If you have fluctuating temperatures, bringing about thaw then freeze, then you will have to be more proactive about judging the safety of the footing.
Get up, get going, seize the day. Enjoy the sunshine, the rain, cloudy days, snowstorms, and thunder. Getting on your horse is always worth the effort.