Hi! WOW -- You leave TOMORROW!!!!!!
Everytime that I've been to Disney, with the exception of 2009, it has rained or stormed at some point! My parents also had rain/storms on their trip the past 2 years. Honestly, mostly it just passes through very quickly! The one day of our trip last June, there was a 70% of thunderstorms. Of course it began to storm DURING the parade at MK, which I was super disappointed about, but it ended up working out fine. We stood in Frontierland & you could actually see lightning bolts right behind Splash Mountain!
They made some minor adjustments to the parade -- I noticed when I looked through my mom's September pictures & compared them to ours from June! Basically, they still had characters on the floats, but they eliminated the walking characters between the floats. I also noticed that the parade seemed to move quicker than usual!
They do shut down rides/shows for lightning, but they don't always shut down everything. Usually everyone does the same exact thing -- hightail it to the nearest gift shop or quick-service restaurant!!! Right after the parade ended (it wasn't raining during the parade, only sporatic lightning) it began to POUR! Well, everyone went to either Cosmic Ray's or the Emporium. We were near the Christmas Shop at MK so we went in there. It was nice to look around for a few minutes, but it was soooo crowded in there. So if it does start raining, try to go into a large gift shop!
When I was a child, there was a huge storm & it rained almost every single day of our trip. But honestly, I don't really remember those things when I think of our trip! We were still able to have a really, really great time!!! So don't stress too much over it! The majority of Florida storms pass through quickly & they reopen the rides fairly quickly. We went over to POC right after the parade & they weren't letting people in because of the storm. The CM said they might close it for a few hours, she wasn't sure. We just sat & waited on a bench right outside (just in case it reopened & to take a little break!) and we ended up having an almost walk-on! I think alot of people leave the park or go to eat once a storm comes along. And alot of the time, if you're one of the first people in line, you can have a walk-on because it takes awhile for people to realize the ride has reopened!
I hope that helps you! Honestly, like I said, I've had rainstorms every single trip & they've never phased me at all! We've always been able to fit all the rides/shows in that we wanted to see & we usually take our time walking around the parks so we aren't rushing to see/do everything.
Have a wonderful trip!!!!!!!! 