Right now the bees have survived our January subzero temperatures without any problem, if they were on honey frames. If a cluster has food during below zero weather, survival is normally is not a problem.
The January thaw that MN/WI is currently experiencing, has come at a perfect time. Right now most bee colonies have been transitioning from the lower box and moving into the top box of hive, Depending how much food was in the lower box(s). Some hives the bees have already moved up and hives that are very heavy with honey, may not have moved up yet.
Once bees have moved up, as the calendar moves to February, brood rearing begins. The queen will start laying eggs. She starts out laying slowly and will increase her egg production over the next few weeks.
This is the danger time for the hive. Once there is brood in the hive, the bees can't move off the brood. If they deplete honey around the brood, the bees have to move out away from the brood to get honey, this feed is used for their food and to keep the brood warm.
Usually getting this honey is not a problem. But if the weather gets in single digits or below for more than one night, starvation can occur. When it gets very cold, the cluster has to tighten up to keep the brood warm. This can pull the bees off a frame of honey that they were using as a food source. The bees will not leave the brood no matter what. The hive will die trying to keep the brood warm.
A beekeeper can help prevent this from happening by adding sugar, candy boards or winter patties. This gives bees some emergency food that can hopefully get the bees over this short cold blast.
feeding winter patties