1. Check the weather before you pack.
2. weather.com is slightly more independent than Disney's KABC.
3. Rule always is to pack layers, and you should pack more inner layers than outer layers. One sweatshirt is all you need. One light waterproof jacket with a hood is all you need (Target sells them cheap, but they are cheaply made, too).
We have been there for T-Day week the past three years. Hasn't rained on us yet, though there was a wind storm and a heavy mist last year. Sunny during the day, cool evenings. Layering is the best idea. Rent a locker in the Park for the heavy stuff for the evenings, t-shirt or sweater during the days.
The key is to take an umbrella with you in the car. If you have it, it won't rain. Forget it, and it will! At least that's our luck! LOL!