I have been 3 times at Thanksgiving. The last 2 times we have experienced great weather. My DD went swimming midday and we wore short sleeve shirts during the day and had a light jacket for night. BUT, the first year we went, it was delightful every day until the day before we left when a cold front blew through. It was freezing! I mean coats, gloves, hats cold. My DN and I made the mistake of going on Splash Mountain at night (we were so excited that we were able to just walk on) and once we got soaked, we never warmed up, even with hot chocolate they were serving.
My advice is to look at the local weather channel weather sites as you get close to your trip just to be sure you pack the right things. You can look at the average temps all day long, but you never know what the weather will bring the week you are there. Just search for Orlando news stations and click on one of them. They are usually the most accurate for 5-7 day forecasts. For the 10 day, you'll have to use weather channel or accuweather. They give you a good starting point, but I end up on local a couple of days before our trip.