I tried to do a snowfall PR - but … it was tricky…
The mechanism to make snow fall in bits and pieces realistically was a bit hacky, it was one of my early contributions, so the code was even more awful than it is now, and the tricks to get it working with tilesets were beyond me.
For example, when it turns winter, in deadpeopletileset, every tile immediately switches to a winter variant, making a system where it only switched to a winter variant when it detected snow on that tile, was full of problems.
However if someone wants to look through the abandoned PR and try and salvage something from it, be my guest - it had a mechanic to pick up snow as an item from the floor, and make snowballs etc.