Looking the temperature of air of the roof

Those who are not accustomed to snow perhaps don't know, how you can sometimes see in the morning only looking from the window to the roof of the building how warm it is. If you have a tin roof as we have, you can see looking this picture, that our temperature is now in zero or a bit + degrees, actually it seems to be 0.4 Celsius.
The tin roof is much better than the felt, snow will fall much easier. Sometimes in spring you had to showel the snow off, if there is half a meter of it, if you are afraid that it will be too heavy load for the building, but now the snow seems to come down by itself.
In the earlier picture of the same building you can see that at that time the temperature was under zero.