Bee hives normally become partially or completely covered in heavy snowfalls. Most hives have a top entrance allowing warm moist air to escape. This helps prevent the creation and build up of ice inside the hives which interferes with the cluster’s ability to keep itself warm. When snow covers the entrance, or the complete hive including the top entrance, it normally is not a problem. In normal conditions snow does not interfere with the fresh air flow through the hive. Most experienced beekeepers welcome heavy snow cover which does a good job of insulating hives against extreme cold and wind.
However in some winters there is a possible danger of ice crust forming on top of the snow that is covering the hives. In a short period of time carbon dioxide will build up to deadly levels smothering the bees. In the past I have lost an entire yard because I did not remove the ice crust and snow in time. I now watch conditions closely and shovel the fronts out only, leaving the rest of the hive covered.
Always being aware of the possible danger of ice crust can prevent unnecessary hive losses.