How do they do in the rain? Do they go back in or do they tend to linger outside and get all wet? If the answer is they linger outside, then they may linger in the snow, too, and not figure out to go in to get out of it. I'd probably leave them in and then open the door when the storm is over. They may not want to step out into the snow, but I have found that if I sprinkle some straw on the snow, they will stand on that. If it's deep and light, watch them, because if something spooks them, they might fly out into the snow and POOF! disappear in. Once they're even half-buried, it's nearly impossible for them to get out again and they'll need rescuing. This has happened to me on more than one occasion. =)