Don't worry - I just checked and the forecast I saw said "scattered thunderstorms" which means it might rain for 15 minutes in the afternoon in Epcot and not be raining at all at the same time in AK, and only a 40% chance of that, which translates into a 60% chance that it WON'T rain.
Even if it doesn rain, it likely won't last long.
Go and have fun! (but don't forget those ponchos, just in case!!)