What?

The winter is symbolic of Finny's temporary victory in pretending the war wasn't really happening.

Only Phineas failed to see what was so depressing. Just as there was no war in his philosophy, there was also no dreary weather. As I have said, all weathers delighted Phineas. “You know what we’d better do next Saturday?” he began in one of his voices, the low-pitched and evenly melodic one which for some reason always reminded me of a Rolls-Royce moving along a highway. “We’d better organize the Winter Carnival.”