Pretty clever idea of using the snow to see the flow behind the car !
Are you going to tuft test it next ?
Tuft testing shows what's happening more thoroughly, and shows just where the flow patterns are on the car.
With a smoke ( or snow ) test you can see the flow just above the car, but you are still pretty much blind as to where your problem areas are.
Here is an example :
There is plenty of turbulence behind the cab on this truck, but the smoke seems to make a perfect arc . It only shows half the story.
An ideal test would be to have both a smoke test and a tuft test at the same time like this one :
