To achieve snow on GTA San Andreas would require a mod, available only via a computer. If you are able to go down that route, suggest you look at the gtawiki site and their modification (and cheats)...
You may need a mod for this. Have a look at this site to see if there is information that would help you:www.moddb.com/mods/gta.../how-to-install-mods-in-gtasa
Its too much to explain here. Go to wikipeadia and search GTA San Sndreas. They will give you the info on how long the game was in production, what kind of gaming engine they used, lawsuits during...