On my way now to check. The bees have ventilation from the bottom of the hive through the inside and out a hole in the shim, but they need to be able to get outside. Or at least feel that they have access to the outside. No one (including bees) wants to feel confined.
Glad I went. The snow was partially blocking the entrance. Removed snow and mouse guard. Using a stick, cleaned out dead bees, twenty or so. Never like to see dead bees but am hoping they died naturally.