Wool falling off of ewe

I have 2 pet sheep who are one year old. They have a very nice shed they live in, but I see them laying out in all types of weather.

I am the only one who cares for them. I say that so you understand that I see them up close and personal twice a day, every day. Yesterday I noticed a tuft of wool sticking up at an odd angle, so I touched it and a huge handfull came off. It's loose like this all along her backbone. The skin isn't broken and the wool has no foul odor. She has never been ill, never off her feed. Do you think this could be from the always-present snow on her back, melting down to her skin? I don't care about the fleece, but I want her to be happy and comfortable. Thanks.