This morning, over the space of a few minutes I was able to see the impact of sunlight on the frost covered roofs of the houses across the street. The temperature was 27 F or about -3 C, but the roofs in the sunlight began to lose their frost.
I began by noticing that the roof at an angle of 45 degrees on the distant house cleared of frost before the shallower angled roof of the house in the foreground. In the photo above, taken just a couple of minutes after I observed that difference, both house have roofs clear of frost that are in direct sunlight.
In this photo, taken just eight minutes later more roofs are almost clear of frost on the far house, while for the near house that clearing is just beginning.
In this last photo only a shaded section of one of the roofs of the far house still have frost. In the foreground, the shaded shed roof, where the sunlight is just appearing, is beginning to lose its frost.