The most recent snowstorm that dropped from 8 to 18 inches of snow on southern New England added more weight to the existing snowcover, leading to multiple roof failures.
Early Thursday morning, the roof of a senior services building in Lynn, Mass., collapsed under the weight of literally tons of snow. Fifteen people were in the building at the time of the collapse. All but two were able to escape unassisted. The other two men were later freed following rescue efforts and were being evaluated for injuries.
The roof of a warehouse failed in West Bridgewater, Mass., in the morning. There were no injuries.
Other roof failures were being reported in Connecticut, in the Wallingford, Somers and Portland areas.
More snow for the weary. AccuWeather.com Facebook fan Matt reported 17 inches of snow at Westfield, N.J., from this recent storm.
The greatest danger of collapse due to snow load is to buildings with flat roofs. Buildings with roofs of this type do not allow the snow to slide off. During periods of melting, the flat surface does not drain well, and as a result, the snow retains the water like a sponge.
The physical properties of a flat roof are such that these structures cannot hold as much weight as a pitched roof. Generally, the greater the pitch on a roof, the more weight it can hold and also the greater tendency for the snow to slide off on its own or allow some the melt water to run off.
The key to a snow's weight is how much water is locked up within the snow. This season, there have been only a few episodes of significant natural melting. Only a relatively small amount of that water has been able to drain off, blow off or evaporate. With this situation, you can literally have tons of extra weight on a roof, because of snow and the water it contains.
While the water content of this storm's snow in New England was less than that of farther south along the I-95 corridor, it was the cumulative weight from this storm and snow earlier in the month that is adding up.
For example, Boston has received about 40 inches of snow this month. A significant amount of that snow and more importantly the water content, 3.50 inches worth, weighs about 18 pounds per square foot, or 1,800 pounds, or close to a ton, per 10-by-10-foot area of roof.
With additional storms likely to hit through the balance of the winter, some big, some small, the risk of roof collapses will continue until a major, prolonged thaw occurs.
There is no sign of that happening anytime soon.
This map shows approximately how much snow has fallen this season. It does not necessarily indicate how much snow was on the ground or on a roof at the same time.
A series of Alberta Clipper storms will swing through the area over the next several days. Most will bring only a dusting from flurries. However, one clipper storm could put down several inches of fluffy snow Saturday into Saturday night in portions of the Northeast.
A train of storms will continue to deliver rain to the Pacific Northwest with one particular storm this weekend likely to be the strongest of the bunch.
A major storm centered on Christmas Eve will affect the Midwest and East with strong winds, areas of heavy snow, wind-swept rain and thunderstorms.
With many winter storms lined up, snow will create a wintry setting for Christmas in some areas.
Several fast-moving storm systems will bring unsettled weather to the British Isles and northern Europe this week.
Residents of Seattle and western Washington will want to keep rain gear handy as wet weather continues to move through the region.
Conditions will turn dry for San Francisco this weekend and last into next week.
Arctic outbreak into Northwest - blizzard ID/ WA/OR - heavy snow coastal sections Walla Walla, minus 20 degrees for new December low.
Arctic outbreak drops low to between 5-15 below zero, setting many records.
Philadelphia, PA (1992)
60 degrees - tied record set in 1928. Only time in 1992 that the city broke or tied a record high.