In regions that have previously not had to deal with heavy snowfall and fluctuating temperatures, ice dams are quickly becoming popular and a problem.  Recent heavy snowfall is causing problems for people who previously did not have to deal with and were not prepared for.

Ice dams are more likely to torment older homes.  Heat travels from attic spaces up through poorly insulated areas in the roof.  When a large amount of snow accumulates on the roof, it acts as insulation and the snow underneath melts.  Eventually the water and ice backs up at the gutters and creates a dam effect.  The damage occurs when the water migrates up the roof and under the shingles.

These winters issues are easily prevented, but must be done so before the snow falls.  It is difficult to remove the snow and ice once it has already had a chance to melt and freeze.  In the short term for those dealing with the problem, removing the snow is the first step.  Carefully and gingerly removing snow from the roof will prevent it from melting and causing ice dams.

Source:  http://www.theosakisreview.com/event/article/id/4745/