I would definitely bring a light jacket or windbreaker along with you, as temperatures will likely remain on the mild side. During the day it'll feel very pleasant with temperatures in the 60s and 70's but once the sun goes down, you'll be glad you brought the jacket. Winter is SoCal's 'rainy season' but it's nothing like the rainy season in Florida, so it's unlikely that there will be a washout. Like teacherlady19 said, southern californians don't care too much to be outdoors during the rain, so rainy days are sometimes the best days to visit Disneyland.
Enjoy!