Wow, I'm going to Disney the same exact dates. Pretty weird. Anyways, coming from a Floridian, weather down here is very strange. The past two times I've been to Disney in December, it's been freezing cold. Other times, it's cool in the mornings and then warmer. IMO MGM is the best park because of ToT and Rock-n-Roller Coaster. I'd also check out Animal Kingdom's Expedition Everest. It's really fun. Magic kingdom doesn't have intense thrill rides but has the three mountains: Thunder Mountain, Splash Mounatin, and Space mountain. All are very fun. Epcot is cool if your interested in the country pavillions and a couple thrill rides. They aslo have an AWESOME holiday display with tons of lights.
Hope i helped!
**Also, MGM has the Osbourne Family Christmas Lights, a huge amount of lights that cover a section of the park. I've never been but I've heard it's very cool**