This is our first time going the 2nd week of Dec, we usually go the first week. (We'll be there Dec 8-12 this year)
From everything I've read, that week is still relatively slow - most kids are still in school. It doesn't start getting busy til it gets closer to the schools being out for the holidays.
As far as the weather, its hard to say. For our three trips in Dec, it was cold our first trip; cool on our second trip; and for our third trip, the first two days was rather warm, but then it turned cold!!!
We'll probably bring jeans & a t-shirt for the day, and jackets or sweatshirts if needed at night. If you go to weather.com before your trip, they do a 10 day forecast, and you can know what to expect!
Have a great trip!!