Here’s the thing. I like your rock, but the snow is really messing it up. It isn’t smooth and from the picture, it looks very glitchy. I highly recommend using blender. Use blender 2.8. It’s easy to learn the controls, and you can model a rock quick and easily. For example, I modeled this rock.
It wasn’t hard at all to model, since it’s a small and simple of an asset to make, and you can easily cover the top or the sides, or whatever with snow! Only a single youtube tutorial about making a snow covered item is all you need. You can download blender 2.8 here.
If you desperately want to do this in roblox studio, maybe try coloring the rock just plain white with the Slate texture. I can’t really think of another way to make a snowy rock in roblox studio.
Hope everything helps and Goodluck!