This would make a great idea for a Christmas party for your son and his friends.
I really wouldn't worry about making snow. He ought to realize by now that it doesn't always snow and be ok with that. But I would get a whole bunch of that angel hair tinsel stuff and hang it in all the trees and bushes and hang snowflake decorations.
It's hard to really give specific ideas because I don't know what kind of climate you live in, how much space you have in your backyard, or what kinds of trees and plants you have.
I really wouldn't worry about making snow. He ought to realize by now that it doesn't always snow and be ok with that. But I would get a whole bunch of that angel hair tinsel stuff and hang it in all the trees and bushes and hang snowflake decorations.
It's hard to really give specific ideas because I don't know what kind of climate you live in, how much space you have in your backyard, or what kinds of trees and plants you have.