Well, we went in Jan. and I think the weather is similar to Dec. Basically, be prepared for a little bit of everything. It does get cold at night--I mean cold! We needed sweatshirts, medium weight jackets, gloves, and hats. Of course, long pants and long sleeved shirts. However, during the day the temperature would be mild, maybe 60-70's, so lighter clothing is needed. I found it best to dress light and take along sweat shirts, jackets, etc. My DH didn't like lugging all the extra stuff around, but was glad to have it when the weather turned cooler. If not, we would have had to leave the parks early due to the weather. But, then again, its unpredictable, so take along some shorts, short sleeved tops, and a swim suit, just in case. Also, take along rain gear. It didn't rain during our trip except for the last day, but we were glad to have rain ponchos. Also, take two pair of shoes for everyone. Nothings worse than putting on a pair of wet shoes the next day! It seems like a lot of stuff, and it is, but better to be prepared than have a trip ruined because you didn't have the right stuff. BTW, I don't bother with nightclothes. Everyone just uses a large tee shirt or sweat shirt, which can double as extra clothing.