Snow forecast before my mouse guards are on — can bees suffocate if the entrance gets buried?

Uppsala, third year, four colonies. We've got wet snow forecast for the middle of next week, which is early even for here, and I'm not ready. Mouse guards are still in the shed, the entrances are at full summer width on two hives, and I haven't put the insulation over the crownboards yet. The question that's actually keeping me up is the snow itself. If a drift covers the entrance and stays for two weeks, do the bees suffocate? My instinct says no — snow is full of air and this has been happening for as long as there have been bees in Sweden — but I've also read that the danger is a crust of ice after a thaw and refreeze, which seals the entrance properly. So, practically: do I go out in the rain this weekend and get the guards and insulation on, which is clearly the answer, and then leave the snow alone? Do people shovel around their hives or is that just satisfying? And is there any argument for an upper entrance as insurance against a blocked bottom one, or does that create the ventilation problem everyone argues about instead?