I saw the following video, and just hammered home that tires are more important than four wheel drive when it comes to traction in the snow:

Being an SUV, this vehicle should have 4WD. But the best part is that the drivetrain is ultimately irrelevant in this situation - if you look closely, all four wheels are completely locked. Thus the only issue is the lack of traction of the tires.

Given the number of cars that slid off this road, it is likely that there is a layer of ice under that snow. While even Blizzaks may have trouble in such a situation, they will still do much better than any all season tire.