Crumbling under the pressure of snow

Icicles hang from a street sign in West Caln Twp. following the precipitation that downed trees, power lines.
Icicles hang from a street sign in West Caln Twp. following the precipitation that downed trees, power lines. (CLEM MURRAY / Staff Photographer)
Posted: February 07, 2014

The Dark Age that has cut off the lights and heat to hundreds of thousands of homes and businesses in the region began with a seemingly innocuous rainfall shortly after midnight Monday.

What followed was what meteorologists describe as an amazingly unfortunate sequence that culminated in one of the region's most disruptive weather events in the period of record, one that sent defeated trees and their branches crashing across power lines and blocking roads.

"It was perfect timing if you wanted to create this type of event," said Gary Szatkowski, meteorologist in charge of the National Weather Service in Mount Holly. He likened it to "the holes in Swiss cheese lining up."

When temperatures dropped to freezing and snow moved into the region at daybreak Monday, that rain on the trees became an ideal epoxy for the snow. The snow was soggy, laden with water, and thus heavy.

North and west of the city, winds remained light Monday morning, allowing the snow to pile thickly on limbs and branches, rather than blowing to the ground. Typically, those enchanting calendar-page scenes quickly deteriorate as the snow melts and plops; however, this time, the snow held with what weather and electric-utility officials described as a rare tenacity. And rarely do two storms hit in such proximity.

Temperatures on Tuesday barely got above freezing, and by the end of the day the trees retained the magical look they had acquired Monday. Neither meteorologists nor utility interests found the scene enchanting.

Meanwhile, the atmosphere was in transition. During the night, warm air moved into the upper atmosphere, while the cold air that remained was dammed above the generous snow cover at the surface.

Much of the rain that overspread the region just before midnight Tuesday was able to bond to the snow as ice, landing before the February sun - which has an effect even behind the clouds - had any chance to stop it.

Up to a half-inch of ice was reported, which is a significant amount, but it did not act in isolation.

"It wasn't really just ice," said Anthony Gigi, a weather service meteorologist who was on duty overnight in Mount Holly. "If you just had half an inch of ice, it wouldn't have been that bad."

But even where the rain wasn't freezing, it found a willing holding area inside the snow, and that added to the weight.

"The snow just sponged it," said Gigi.

The rain was steady, but hardly a downpour. Had the rain been heavier, it might have dragged down warmer air to the surface.

"Nothing worked," said Gigi.

By the early hours Wednesday, many branches and limbs probably were attempting to hold an inch or more of liquid; an inch of water over a square foot of surface weighs about 5.2 pounds. That adds up.

The stress was too much for weaker trees that had never been pruned, said Eric Vorodi, an arborist who is president of About Trees Consulting in central Pennsylvania.

Particularly vulnerable, he said, are the white pines that are so plentiful in this area. "White pines tend to be somewhat brittle," he said.

Unfortunately, he said, this region has an abundance of "volunteer trees" - trees that spring up on roadsides on their own, not tended by humans. Some of them wound up on the roads Wednesday.

"It's the one-two punch that did us in," said NBC10 meteorologist Glenn Schwartz. "It's very rare to see such storms so close together. Bad luck."


twood@phillynews.com

610-313-8210

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