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Why so many trees came down under the snow

Snow that accumulated sideways, blizzard-like conditions and the of weight of snow led to 800,000 power outages.

A SEPTA bus is covered by a tree that slammed into its roof on Friday.
A SEPTA bus is covered by a tree that slammed into its roof on Friday.Read moreMICHAEL BRYANT / Staff Photographer

Friday was not a good day to be a north-facing surface.

While accumulating snow is a staple of winter around here, usually it doesn't accumulate sideways. Yet on Friday, that's what happened.

Driven by those ferocious gales from the north, snow became snow super-glued onto the north sides of tree trunks and their branches. That likely contributed to the taking down of an astonishing amount of wood, said Paul Meyer, executive director of  of the Morris Arboretum in Chestnut Hill.

One of the trees the arboretum lost was a Norway maple, on the grounds since at least 1932. Its roots can be traced to a nation that has known winter.

"It snapped 5 feet from the root, which is very unusual," said Meyer.

The sideways snow exacerbated the impacts of the winds and the heavy snowfall.

The winds gusted to 60 mph. "There probably were blizzard-like conditions," said Valerie Meola, a meteorologist at the National Weather Service in Mount Holly.

And as the day wore on, the trees had to contend increasingly with the sheer weight of the snow that landed atop the branches as well as the wind. The branch of a mature tree can radiate 20 to 50 feet.

Had the snow never materialized, the wind alone, would have resulted in power outages. But the snow undoubtedly pushed this storm into the PECO hall of fame, with more than 600,000 outages, No. 3 on the all-time list.

Outages were widespread on both sides of the river, and of note, a dense cluster rippled along a corridor from central Delaware County across the Main Line into Montgomery County.

Those areas also were among the most-snowed-upon in the region, with totals of six to nine inches reported, possibly bearing the typical water weight of a foot of snow.

As for weathering Round II this week, the winds won't be nearly as strong with the midweek nor'easter, nor will they last as long. But more heavy, wet snow is possible. In any event, the Wednesday morning and afternoon commutes are not looking pleasant, Meola said.