Create snow particles around you, think in reverse when it comes to creating the settling snow. You should determine where the particles land, not where they spawn. This way you know where to spawn settling snow. The only thing left, is to spawn voxels of snow around the point where the snow lands.
I made a prototype game a few years ago, that uses that reverse mechanic with raycasting, so that meteors always will land within the playing area. You can check it out here: Time Hunting - Roblox