Here in PA and nearby by areas of the mid-Atlantic or Northeast we had very warm record setting 70F weather last week and last night we had a deep freeze, 5F. The danger is that the mild fall and first half of the winter may have kept the sap flowing in rhododendrons and azaleas. Then when we get a sudden deep freeze with the sap flowing, the sap freezes and bursts the stem, the vascular structure and ruptures the bark. It is almost always fatal. However, if you find a plant with bark split damage, you can treat the plant as you would a graft, using a rubber grafting strip, tape, or grafting twine. Then seal the entire graft area with warm grafting wax or grafting paint. Remove the rubber or twine shortly after the damaged area has healed. Never allow the binding material to girdle the stem. These precautions will seal out disease with wax and provide a rubber covering to provide support and protection, and can sometimes save the plant.
A friend (rhizo_1) reminded me that "sometimes these ruptures hide themselves until later on in the season. Perhaps the outer bark itself doesn't split open until the heat of the summer, or the lesion is buried in mulch, etc. I've seen both happen numerous times in SC. Of course, by then it's too late to even think of attempting a repair. I'll be quite surprised, this spring and summer, if we don't see a lot of frustrated people writing in to many of the forums about their sick or dead shrubs."