During the opening sequence, when the car is being driven through the mountains, there is plenty of snow around. When the car enters the tunnel, there is suddenly no snow anywhere, nor is there any when the wreckage of the car is pushed over the edge into the river.
I live in Turin (properly known as Torino)and in the alps, during the summer/spring when this movie was filmed, it is not unusual to see snow in some places, and not in others.