Hi, Christine, and thanks for bringing another great question to the Disney Parks Moms Panel!
While rain during your Walt Disney World Resort vacation might be inevitable, you definitely shouldn't let it put a damper on your plans! Make sure you're prepared each day with essentials like ponchos and perhaps a small travel umbrella and you can carry on even when the rain begins to fall. Typically the only reason outdoor attractions are closed is if lightning is in the area, so if it's just a little rain you'll still be able to experience almost everything.
My family and I have made some of our most magical Walt Disney World Resort memories playing in the rain at
Magic Kingdom Park, but in the event of a real gullywasher you'll want to seek out indoor attractions and shows such as Walt Disney's Carousel of Progress, Monsters, Inc. Laugh Floor, The Hall of Presidents, The Country Bear Jamboree, Walt Disney's Enchanted Tiki Room, and Mickey's Philharmagic. (These are also wonderful attractions to pepper throughout your day as each is comfortable and air conditioned!) Other experiences with indoor queues and attractions include it's a small world, Peter Pan's Flight, Buzz Lightyear's Space Ranger Spin, Space Mountain and Pirates of the Caribbean. You can also visit Princess Fairytale Hall and Town Square Theater to meet some of your favorite Disney Characters indoors, too!
All-in-all, you'll find plenty of places to wait out the rain and you'll typically see wait times drop for many attractions once the rain starts as people typically head out of the Parks then. Visiting attractions such as Seven Dwarfs Mine Train, Space Mountain and Splash Mountain during events like the Festival of Fantasy Parade or Happily Ever After is another great way to experience lower wait times, too.
Enjoy your Walt Disney World Resort vacation, Christine!
Amy