Icing problem on roofs in winter:

A phenomenon where when accumulated roof snow begins to melt when temperatures are just near freezing and remain so. The ice on the roof above the living areas starts to melt, but not above the overhangs. 

The water runs down to the over-hang area and then freezes building up ice . This dams up the water flowing down and then it creeps up below the shingles or tiles and causing a leak to your living area.
Under these conditions clear the snow from your over-hang areas. Or you can install deicing electrical heating systems...such a pain to do!

Fortunately here in Squamish this year, so far, we have not had these undesirable conditions for this to happen. But I have experienced it in the past. Fortunately the temperatures quickly rose way above freezing very quickly. Rain helps, don't knock it!