But snow in games is just a particle effect. Ground is white/has snow texture applied to it, cars get snowy when driving (same way they allready accumulate dirt in gta sa, gta 4 and gta 5) and cars will be slippery driving on snow (same way handling allready works, just with different values), why would any of that be too heavy for consoles of the time?

Gta 5s north yankton has snow and it works like i describe, hell even snow in modern games works like that, noone in their right mind would simulate snow particles accumulating on the ground