In respect to tovelling dishes in the snow, this discussion concludes that who knows what the Shulchan Aruch holds, but the Rema allows such a practice in times of need.
But just how much snow? After all, water expands when frozen. Must one use a mikveh of 40 se'ah of water, which could be as much as 800 se'ah of snow depending on how densely packed it is, or can one use a mikveh of 40 se'ah of snow, even though that's much, much less than 40 se'ah of water? That is, once we've said that snow is mutar b'sha'as dechak, does this mean it has to contain the same amount of water as a normal mikveh, or the same volume as a normal mikveh?