I concur regarding the avalanche snow and the ones that survived the longest managed to curl their body so they kept an air cavity in the snow. You basically don't want to end up spread eagled inside a drift where you can't move anything.
I would also concur with insulator that the snow on the ridge vent wasn't entirely the cause of the moisture in the attic but it didn't help it either. That said, sealing off the attic so the moisture doesn't get in there probably should be done but it also just traps the moisture in the house below it so that doesn't change the fact that you need some type of totally integrated environmental climate control to deal with the moisture. With all other variables remaining the same, every action has a reaction. If the house below the ceiling can still dispell the moisture then you get lucky.
Many older houses already have their own passive system where the outside atmosphere integrates with the interior by moisture and air escaping through doors, windows, walls, ceilings, vents to the roof/wall/soffit, etc. The tighter the house becomes, the more we have to start using mechanical systems to get rid of moisture and old/foul air. The tightest house of all would be a moisture proof and air proof plastic bag/bubble/balloon which is almost what we are turning houses into with all the sealing, plastic, tyvek, caulk, vapor barriers, etc. that we do. You couldn't live very long in a plastic bubble without mechanical ventilation.
Enough said, I think everyone should get the point.