Snowstorm is one of the Achievements a player can accomplish in Audiosurf. To attain it, the player must cause a chain reaction seven or more White blocks. Thus, this requires the use of any non-Mono character.
Snowstorm can be achieved in many ways, but this is a sure fire way of getting it.
First, choose a long song, the longer, the more white blocks you can pick up, I use Steve Reich's Piano Phase, lots of traffic, 24 minutes long, but you can use any. I recommend doing this in either Double Vision Casual or Pro.
As soon as possible, make a "base", that will stop the white blocks automatically going up, use a common color, blue or purple. In the first lane from the left (keyboard side), hit a purple or blue. Leave the second lane on the keyboard side clear. Hit 2 more purple or blue blocks on the right 2 lanes (mouse side).
Now you've got your base, just cruise along in the shoulders until white blocks come your way. Leave the second lane clear, do not put anything there yet. Keep sitting in the shoulders only picking up white blocks until you've got 7 or more.
Finally, in the empty second lane, hit the next blue or purple block that comes along, and watch 'dem blocks disappear.
Congratulations, you have unlocked Snowstorm! You don't have to finish the song, you can end it right after you get the achievement.