Hi there Jesse,
Welcome to planDisney and thanks so much for your question!
Rain can definitely be a downer if you're not prepared for it when visiting the Disneyland Resort. However, when I have been prepared for it, some of my favorite memories of visiting the parks were on rainy days - including a day last December when visiting with all of my planDisney pals!
Having said that, I can most definitely understand not wanting to
navigate inclement weather. Luckily, it's easy to reschedule your
theme park reservation through the
My Plans hub on the Disneyland Resort website!
Theme park reservations are subject to availability and depend on the type of ticket you're using, but when looking at the
availability calendar, it looks like there are still reservations available on the days around December 21st. It's possible you might be seeing the dates grayed out because your ticket already has reservations associated with it, or maybe you're using a ticket or Magic Key Pass with blockout dates?
Still, it's worth looking on the My Plans hub and attempting to modify your current reservations to a different date. If you're still having trouble and think you should be able to move your reservation dates, then it might be worth
calling a Cast Member at the Tickets line to get more detailed information about your specific situation.
Thanks again for your question! I hope that you have a fantastic visit to the Happiest Place on Earth.
Have a Magical Day,
Greg