Hi Nancy,
Welcome to the Disney Parks Moms Panel and thank you for asking us a question!
While you can definitely purchase
Special Event Tickets on the day of a given event if it isn't sold out, if you’re visiting Walt Disney World Resort specifically to attend
Mickey’s Not-So-Scary Halloween Party, then I strongly recommend purchasing your tickets as soon as possible, especially if your visit is closer to Halloween (when Party dates often sell out).
While there are no refunds or exchanges allowed due to inclement weather on the day of the Party, I can promise you that I’ve experienced the Party in the rain and it really wasn’t that bad. The rain was largely short-lived and, if anything, it helped cut down on the crows in the Park which was an unexpected bonus! If you’re really, really worried about rain, my best suggestion would be to wait until your vacation dates fall within the long-range forecast for the Orlando area. You can try to pick your dates based on what seems to be coming, but don’t forget that forecasts can change at any time.
Please don’t hesitate to come back and see us if you have any other questions.
Have a Magical Day,
Lynne