I posted something within my thread about packing, you can find it here:
http://disboards.com/showpost.php?p=48996051&postcount=2
To summarize -
I've been keeping up with the weather down there, and it's been around around 70-80.
I usually only pack one or two pairs of shorts. Honestly, even with temps in the 70s, I usually wear jeans and a t-shirt.
A solid indicator is the sun and temp (obviously, but hear me out..) In December, I've come to realize that the sun and temp decide how cold it is at night. I've been to Disney when it dropped down to the low-40s at night, and I've been to Disney when it's been high 60s and gorgeous.
- If it does not hit 70 during the day, or only hits 70 at 1pm then starts dropping down, it's going to be a cold night. -- especially if it's cloudy outside.
I usually pack for "Spring" or "mid-Fall", then pack additional layers for extreme weather. In NY, Spring and Mid-fall are right in line with December weather in Florida. It could be nice and warm most of the time, and you could be comfortable in jeans/shorts and a t-shirt/thin long sleeve shirt. But, sometimes it does get pretty cold. So along with my normal jeans, long sleeve collared shirts, and thin long sleeve shirts, I pack for:
Slightly colder:
- a Sweater or fleece to wear over the shirt
- A hoodie
Colder:
- a coat (I wear down when I fly)
- Sweatpants
- thermal shirt
- gloves
- scarf
- sock hat
If it's a little chilly, I'll layer a shirt with a fleece or hoodie. If it's pretty cold (50's) I'll go with the coat. If it's very cold, I'll layer the hoodie with the coat or even the thermal and gloves and a scarf. Good luck!