We went the last week & a half of January 04. Temps ranged from sweatshirts & shorts in the AM, ditch the sweatshirts around noon, and sweatshirts/pants in the evening. Not much rain- 1/2 a day, maybe. Some days, needed the sweatshirts all day. We're from Maine, so we even went swimming one day. Would've gone more, but were too busy.
Crowds were light enough - not too long of a wait for rides. Think the longest was RNRC - 60 min with fastpass - but that was because we waited until the afternoon.
All in all, a nice time to go.