We ended up going with a VGA projector playing a loop of falling snow against the cyc. The windows and french doors were covered with scrim and it ended up working out pretty well. There's a lot of thunder/lightning cues so I've got a few fixtures on a tree behind the set that light up the back of the scrim and that's been working pretty well.
My only complaint is that the snow is pretty big, with the resolution and the distance of the throw there wasn't much that could be done about it, but it's not distracting and it gives the necessary illusion.
I think if I could've wrangled another projector we might have been able to do it a bit differently, but for what it's worth this isn't bad and it gets the point across.
Thank you all for your input!
My only complaint is that the snow is pretty big, with the resolution and the distance of the throw there wasn't much that could be done about it, but it's not distracting and it gives the necessary illusion.
I think if I could've wrangled another projector we might have been able to do it a bit differently, but for what it's worth this isn't bad and it gets the point across.
Thank you all for your input!