OK, good old Colorado. Yesterday it was in the high 60s, it started snowing last night, accumulated about 5 inches of snow during the day. Tonight it may drop into the single digits, but should be back in the 50s by Friday. This is my first winter with chickens. I have eight almost 5 month-old pullets, all cold hearty breeds. I've built them a 4'X8' coop that I think is pretty well built and has decent insulation and I spent a bunch of time this weekend with the calk-gun reducing drafts around the main door and the egg door. But I'm still unsure about how to keep my little flock safe and happy during the winter months. I opened their pop door as usual this morning, giving them access to their enclosed run, which is built inside a large out-building (see photo) that protects the run from most of the snow and wind. They spent most of the day out in their run (high of around 27 degrees today) but were inside a good hour before dark. At what temperature or weather conditions do I keep them locked inside their coop? Can I continue to let them out to free range during the day during the winter and if so, in what conditions? At what temperature do I provide an additional heat source inside their coop? Any other good advice for me?