We visited WDW both late/January and early/mid February - strongly suggest LAYERS. Mornings can be very chilly, mid-day can warm up to low 70's, and then drop back down again by early evening.
Hint: Fleece is light weight, a good air block, more water resistant (& dries faster) than other materials and doesn't wrinkle. I stuff a fleece jacket, scarf and gloves into my day bag. For good measure I also take a little battery operated fan for surprise HOT days. I never go without a hat for sunburn protection and shade - that Florida sun gets bright!
I wear loose fitting light weight slacks (cotton/spandex blends) that block wind and dry quickly. DH refuses to wear anything but jeans - and paid dearly a couple of times in rainy seasons. Jeans get cold and heavy when wet.
Also a variety of cotton/silk shells, button front blouses/shirts, pull over tee shirts, anything you can mix & match but also remove in public in case it really warms up. would be good.
Plan to do Splash Mtn/Kali Rapids later in the afternoon when the weather warms. We don't do Kali AT ALL because of the intentional 'dousing' by fellow guests at the end of the ride.
If you want to ride early and avoid wetness, take large trash bags with a slit in the bottom for your head but do not make armholes. When you get into the ride, quickly pull the bag over your head and hold your belongings (and shoes if you don't want THEM drenched) in your arms inside the bag. I know it looks silly, but it saved our whole day!
Splash Mtn is relatively easy - don't sit in the front of the car and you will avoid most splashing. Most of the wetness on this ride is waist down. You might take a trash there and wrap it around your legs - or put your feet into it (no slit for your head this time - you're working from the bottom up) and pull it up to your waist.
Okay, by now I can only imagine the mental picture you have of me - bundled head to foot in fleece gloves, scarf, jacket, layers of clothing, a large brim hat, sunglasses, sunblock, carrying an armload of plastic trash bags and holding a little battery operated fan.
Yikes! Really, it is not that bad. We take a small backpack that also has wheels so we can pull it along. Most of the time we rent a locker and leave it there AFTER the morning chill has left and we have striped down some.
DH hates to carry anything - including the camera/camcorder, so I have a small fanny pack for those items and my water bottle - well that just inhanced that mental image huh?
My momma always said "better to have it and not need it than to need it and not have it" so that is my life motto. Pick and choose from the advice above - but whatever you do - HAVE FUN! If you clothes get wet, go on some indoor rides until they dry or go back to your room and change. WDW is a place of magic and dreams so ENJOY it all! :thewave: