I go every year the day after Thanksgiving and let me tell you it really can go either way.
I'm from NH- I'm used to the cold but for some reason when we are at the Magic Kingdom on Saturday night it is usually very cold. I always wear a long sleeve shirt, a fleece vest and a scarf, bring gloves because when your standing around waiting or even at World Showcase for Illuminations in Epcot it can be real cold. This time of year you have to plan for both warm in the day and cold at night. I guess it would be different if we were going from a car to the house but we are usually outside all the time so it's pretty chilly.
Not to worry as soon as the temp dips, gloves, hats and scarfs come out at the counters along with Hot Chocolate.
Enjoy your vacation, it will be so beautiful not matter what the temp.
denise