Ok, finally, here is the BEST WAY to make snow in UEFN. I put a few sample displacement maps over on Patreon if you want to help support this channel, if not, go get your own! There are lots of them out there for free for sure.
https://dev.epicgames.com/community/learning/tutorials/R84B/fortnite-the-best-way-to-make-snow-texture-and-snow-biome-in-uefn