It is a sudden release of snow off a rooftop. Falling snow forms a temperature-sensitive bond to the surface of a metal roof. As that roof is warmed, (through an invisible spectrum of sunlight or from building heat loss), the bond with the snow is broken and a thin film of meltwater lubricates the roof. This causes a sudden release from a rooftop that can dump many tons of snow below the eaves in a matter of seconds, endangering building elements, landscape, vehicles and pedestrians. Click to read more.