[Most of the old legends didn't make it through the war and she was raised by a scientist without much imagination. That Indrani had no reference point for childish belief wasn't unreasonable, weird as it was by most metrics. But at least she's heard of one of those.]

I think I read about Santa Claus once, but the book was half burned out, so I didn't really get very far. And I follow your astronomy. But I'm betting snow is one of those things that didn't make it through the war. I guess the river gets a little gross and cold for a few months, but that sludge couldn't freeze above absolute zero with all the sludge there is down there.