How does the snow act as a metaphor for the war?

It's more the cold than just the snow. Gene observes the "single, chilled points of light" in the sky, trying to find guidance in them; what he sees is not beautiful or ideal, and he tries his best not to have an optimistic view of war like the others. He takes the cold, remote looking stars as symbols for the war, and ascribes their qualities to the war as well. Also the snow covers the railroad tracks and the boys feel part of the war effort when they have to clear them for the soldiers.