Hello, Brittany!
Thank you for visiting the Moms Panel. You are wise to be thinking about the weather for your upcoming trip. Rain showers do like to make appearances while you are on vacation just to remind you that Mother Nature never takes a vacation.
I always pack 5 ponchos to cover every member of my family. Ponchos are a "must" for every Walt Disney World visit. I would advise purchasing ponchos that are not too bulky and very lightweight. I can fit my 5 ponchos inside a gallon size bag and slip it at the bottom of my backpack. Also, purchasing your ponchos outside the parks will save you money. I do, however, always carry very small umbrella that can easily fit in my backpack. Some of the rain showers come in very small amounts. This is when I love to just take out the umbrella for myself. My husband, boys and many WDW guests welcome the rain due to the heat. Now there are times when the rain comes with a vengeance and an umbrella will simply not keep you from getting soaked. This is when we pull out the ponchos. When you are in the parks, you want to keep moving in order to enjoy the parks and a poncho allows you to keep doing this. Also, with a heavier rainstorm, many people begin pulling out their umbrellas and it begins to get very tricky when you are trying to maneuver around other umbrellas when yours is out. It also gets you mean looks because everyone is trying to get around your umbrella. People tend to get cranky because of the rain!
Well, if I had to make a choice, I would say keep the ponchos with you and leave the umbrella at home. I just wanted to give you a glimpse of what I choose to do with every visit. I hope your vacation will be filled with "Disney Magic" and no rain showers. Have a magical day!