I would say that is plenty warm, and I bathed one of my horses today and it was in the 50s, sunny, and minimal wind. I used warm water, and then I dried her off to the best of my abilities and then she was put in her stall. Horses are tougher than some people give them credit for. If it would have rained today I guarantee that all of my horses would have stood outside, gotten soaked and loitered in the pasture even though they have a shelter. My mare was damp and she didn't care about anything but eating her hay. As long as an animal is healthy, strong, and well taken care of they should have no problem in the cold, wet weather even without a blanket. Just my experience. I would use a rug if I had to on my oldest horses if they were taking winter particularly hard, but other than that and showing none of my horses have seen much of blankets.