When the temps are that cold it really helps if the sun is out. They'll sit in the sun to get warm like most animals. With those temps on a cloudy day they will most likely be in a hole. Two weeks ago I hunted a small patch of woods when the sun hadn't quite hit it yet and came up with a little barking on a cold scent. After the sun was laying in there, maybe 1/2 hour to an hour later I went through again and got 3 rabbits up. It was in the low 20's that day.