Symbolism, Imagery, Allegory
That deal about nature going on in the midst of war is something you find throughout the book, though rarely quite so prominently as it is in the snow case. Usually, it's a bit subtle – when the characters are engaged in some activity, an animal shows up, going its merry way as if everything's totally fine. For example, when Robert Jordan is rigging the bridge with explosives in a life-or-death operation and sees a trout in the brook below that has no idea what's going' on above:
As he looked a trout rose for some insect and made a circle on the surface close to where the chip was turning. As he twisted the wire tight with the pliers that held these two grenades in place, he saw, through the metal of the bridge, the sunlight on the green slope of the mountain (43:37).
Ah…quite a contrast between the grenades/wire/pliers and the trout/sunlight/green mountain slope. Depending on how you look at it, you could either find this comforting or disturbing. Comforting, because not everything is screwed up or in chaos, even if war makes it seem that way. Disturbing, because nature herself doesn't really care what human beings are doing to each other.