Note the semi-detached house in the centre of the picture. The near half, with the square skylight, has a totally bare roof. No snow cover. It melted away. From heat loss.
Note the second half of the house, covered in snow. Better insulation, possibly better attic ventilation too.
Here is a view of the warehouse roof outside my third floor windows. First built as the Champagne streetcar barns, then called Vimy House, now it’s a secure document storage facility (know to us plebes as a mini-warehouse). The roof structure on the original building is 2×4’s or 2×6’s set on edge and packed together. Some sections had rot, when repaired Metcalfe Realty replaced them with trusses. The roofers put sheets of foam insulation on top before reroofing. Every repaired spot sticks out like a sore thumb, marked by a clear-melt zone. Cold storage anyone?