During a snowstorm as snow piles up on the roof, the sunlight is occluded from the roof, and snowpack is retained on the roof by two different bonds. There is a temperature-sensitive frictional bond between the blanket of snow and the roof.
There’s also a cohesive bond up at the ridge. One blanket on either side of the ridge co hearing to each other. And it’s a combination of those two bands that are resisting the drag load or gravity load of the snow, which is trying to slide off the roof. So, there are both frictions involved as well as a cohesive bond.
If the vector forces that drag load exceed the strength of those two bonds, then the avalanche will occur. So, what happens is the next day when the storm is dissipated, and the sun comes out, the sun’s rays shining through the slightly translucent snow warms the roof surface under this snowbank.
When the surface heats up, this temperature-sensitive friction lining is released. This bond is not only released, but the roof is also lubricated with meltwater. The entire drag load now is experienced by the cohesive bond at the ridge, which is too weak, and thus, the avalanche occurs.