Hi Rachel!
Thanks for your question. Get ready to be ghoulishly delighted at
Mickey's Not-So-Scary Halloween Party at
Disney's Magic Kingdom! From the trick-or-treat stations, to the Boo-to-You Halloween Parade, to the amazing
Disney's Not So Spooky Spectacular fireworks show, there is no party I'd rather be at Fall season than this spooktacular Halloween party! :-)
So this is the official verbiage regarding Mickey's Not-So-Scary Halloween Party related to inclement weather:
"Entertainment may be cancelled due to inclement weather or otherwise. No refunds even if entertainment is cancelled."
Disney places a premium on safety, for its Cast Members, characters, and certainly all Disney guests. I do know that they closely monitor weather forecasts, and, weather permitting, sometimes they will delay the party (if the storm is just passing through) or delay party activities until the storm passes. If it turns out to be a major storm lasting hours, than there is a good likelihood that the party could be cancelled.
Here's to hoping for clear skies and a beautiful night on the day of your party!
Terry