now, I may be the dissenter here (or I may have been lucky) This fall was very warm in Europe, but it did get very stormy the first week of Dec. I went to DLRP several times and really struggled with the temperature. As a guide, the warmed was about 12 degrees celcius, the coldest right around freezing with very strong winds.
First wearing a wool sweater, wool peacoat, and scarf at night - was dripping with sweat. Then wore a wool sweater with tshirt underneath, and scarf - much better. During the stormy weather I finally relented and wore my peacoat, but with a tshirt only underneath. The peacoat was only because wearing a sweater earned me odd looks.
Frankly, I am no longer used to the heat indoors in Europe. Going into Blue Bayou, POTC, many of the shops, rides, etc is just difficult when they are so warm inside.
So my thoughts are layer layer layer. Wear a tshirt with a sweater on top and a wool coat. Take hat/mittts/scarf. Prepare to use a locker. Prepare to remove/add layers as required.
I love going to WDW when it's cold, and was a little disappointed that I wasn't so cold at DLRP...