Also this increment in weight of the roof causes the structure to Snow also causes leakage and moisture build up because it can easily seep through the cracks as it melts. Snow is also know to cause ice dams which occur when snow inhibits proper flow of water from the roof causing it to leak and accumulate inside the house. This can cause major water damage to your property requiring expensive roof repairs.
When strong winds blow over your roof, they reduce the pressure on the roof way below the pressure below the roof. This difference in pressure is what causes the roof to be pushed upwards.