There's a lot of snow at the end of the novel. It starts to build and build as the job comes together, especially as Kat has doubts about whether or not she can pull it off. On the morning of the heist, Kat notes, "something about the snow filled her with dread" (30.1).
She has no reason to worry, though. The day warms up, the heist goes off with nary a hitch, and Kat emerges into "the fresh air. A clean start" (34.43). Another clear, beautiful day, perfect for planning the next heist.
So what's the snow all about, then? We think the snow represents Kat's anxiety, and the increasing complications of the heist job. But just like our own worries, the snow dissipates once Kat's plans are realized.