hmm. well it looks tons better. any place i can get a hold of that ? been looking for hours on google and youtube :P apperently its this mod https://www.gta5-mods.com/scripts/singleplayer-snow
'' this issue already existed in GTA:Online (snow inside cars) as Tunables where modified and snow appeared (back in April 2015). See this video https://youtu.be/jxbOZPZzlYM?t=792
So it seems to be a common shader or material problem of vehicles that snow get's placed on it. I'm afraid we won't be able to fix it until Rockstar will fix it (They have to as they'll put snow in GTA:Online in December).'' seems it was in orignialy, but it seems they never fixed it so they removed the snow on cars instead :(
Last years Xmas it did. but had some snow in the interior of the cars. but overall looks way better than without. just look at th second screenshot of the mod page.
or this link https://www.youtube.com/watch?v=63-bc1118K8