I noticed when i was driving. there was maybe a quarter inch on my car. The snow would fly off the hood.. but would actually be pushed against the rear glass. Im pretty sure the air is moving in a circle over the rear spoiler.

Not sure if it's circular, but it does give some downforce as the air flows over the roof of the car and down the back window. It snowed here in sunny Florida around Christmas of 89. My Dad didn't believe it, so I drove my 85 Charger down to Tampa and there was still snow on the car when I got there. Deal was, he had to eat snow off the car. Let him off after a few mouthfuls.