It doesn't look like you have a lot of snow in the picture, so if you installed a carefully hung heat lamp inside and only let them out when it's sunny for a bit, they should be fine. A lot of people hate the thought of heat lamps in coops for good reason, but I've never had a problem with them. I only use them in extreme conditions, or with littles. I wouldn't put them out there much before 8 weeks without heat.