How to properly vent attic in windy/snowy areas to avoid snow infiltration?
This is a common problem here in the north country. Normally, soffit vents are fitted with Styrofoam tunnels called "proper vent" that rest on the soffit vents and snug between the rafters and extend apx 3 feet up the roof. Your insulation is then placed around the bottom of the proper vent. Snow rarely will make it all the way up this Styrofoam vent extender. Does your roof have a ridge vent? Most houses that have soffit vents also have a ridge vent. The idea being that the cool air enters at the soffit and warm air exits out the ridge.  The only other suggestion I would have is to buy a few rolls of ridge vent filter material. Cut this material into pieces to fit over the exposed soffit vents between each rafter.