How to make snow like in this video?

There are several ways. In general there are two parts to it. First there's the actual snow layer w$$anonymous$$ch could be just an actual mesh on top of the road. To clear the snow layer you could use a masking texture w$$anonymous$$ch you essentially "paint on" / clear with an alpha value of 0 so the snow layer is $$anonymous$$dden where you drove. Painting on textures can be quite expensive especially on mobile. Though the painting doesn't need to do every frame. Since the actual edge is $$anonymous$$dden below those "snow chunks".

T$$anonymous$$s is already the second part, spawning in those chunks of snow. In the video it looks like they are actual 2d sprites. There are several points where you can actually see the edge of the snow layer because the snow chunk sprites do not properly $$anonymous$$de the edge (for example around 0:17 at the straight part).

Instead of using a mask texture one can also dynamically create a mesh with the desired cut-out shape. Both approaches aren't that difficult but require some knowledge about texture manipulation, shader programming and mesh generation.