Bearding! Thanks Joe D. A quick google search with articles and images reveals this must be bearding and explains what causes this (heat and/or crowding) and that this is typical behavior. Boy, do I have a lot to learn!
Better.to.Bee... I'm in Colorado, near Boulder. Average highs in the coldest months of Dec/Jan are in the low-mid 40s, but can often get to 70. Lows at that time are in the low to mid-teens, sometimes well below 0, but only for a couple days at a stretch. A local top bar beekeeper advised to leave 15 or so frames of honey to get them through winter. Better to leave them some extra and then take off any excess in the spring I suppose. Besides, I think more honey in the hive means more thermal mass that will help hold the temp in the hive over winter.