I admire you trying such difficult subject as a snow! Especially in braille scale! But... there are several "buts":
1. I wouldn't call it "a diorama" for one reason - there is nothing going on. Diorama usually has some narrative in it, some kind of a story, or a plot. Here is just a model with a little "stand".
2. It doesn't look like a snow much to me. More like some white "dirt" was dumped and smeared all over it. Try to look around and take pictures of snowy vehicles for your own reference. Try to notice where the snow usually get stuck. And what it looks like.
Maybe the model looks fine in a real life, but while being enlarged on the photo, it allows all the problems to be visible.
Again, everything I wrote above is my own opinion. IMHO - as long as you like what you do and see ways to improve - that is what counts.
If anyone knows about this topic more than I do, I hope I will be corrected.
My models and more...