The science and power behind ice storms
Last week, while much of the state got rained on, I got iced.
I live on the northeast edge of Litchfield County. In my town, and the towns nearby, it was cold enough at ground level that the rain froze when it fell on tree limbs, railings and clotheslines. The birches in my yard were suitably bent.
A lot of this had to do with elevation and cold pockets of air — when I drove east, downhill, the ice was a no-show.
Nor did the rain — which forecasters first thought might glaze larger parts of Fairfield and Litchfield counties — freeze much of anything there.
“We measured .08 inches of ice,’’ said Gary Lessor, director of The Weather Center at Western Connecticut State University in Danbury. “We knew by Saturday it would be less than a tenth.’’
Matt Spies, of Brookfield — state coordinator of CoCoRHAS, the Community Collaborative Rain Hail and Snow Network, which uses a corps of volunteers to collect precipitation data — said by the time he checked his gauges, the little ice that might have been was washed away.
“I got a half-inch of rain,’’ Spies said
This is one of the problems of ice storms — they can weigh heavily in some towns, and lighten up a few miles away. They’re largely unstudied and hard to calibrate. Rain falls into gauges, snow gathers on the ground. But how do you measure ice — radially, on the branch of a tree, or horizontally, on top of a flat surface?
But when the temperatures and storm patterns line up correctly, they have the potential to do serious damage to the environment, as well as make human lives miserable. The events of last week showed that, with icing shutting down a good part of the Southwest U.S.
Because that storm caused minimal problems here, we could dismiss it as something happening in Texas. But the rain and ice we got was part of the same system that proved a killer down south.
“These are massive winter storms,’’ said Bill Jacquemin, senior meteorologist at the Connecticut Weather Center in Danbury.
Ice storms happen when a layer of warm air flows into a column of cold winter air, while a narrow layer of freezing-temperature air gets trapped at the earth’s surface. If snow falls, the warm air melts it into rain. When it hits the earth, it freezes on contact.
Jacquemin said a hard, steady rain doesn’t convert into an ice storm, because the rain washes away the ice as it forms. What’s needed is sustained drizzle and mist. Then, the ice accumulates.
When that happens, the weight of the ice downs tree limbs. Those falling branches, in turn, take down power lines and make travel treacherous.
“Even if there’s a blizzard, people think they can drive, if they give themselves more time,’’ Lessor of Western’s Weather Center said. “People are afraid of ice.’’
New England generally gets a moderate ice storm every five to 10 years and a severe one every 35 to 85 years.
In 1898, a severe ice storm shut down the state’s Northwest Connecticut, with witnesses saying the sound of tree limbs cracking reminded them of July 4 fireworks.
On Dec. 16, 1973, another severe ice storm caused a third of the state to lose power. That storm caused more damage to Connecticut’s trees than the Great 1938 Hurricane.
There has been recent work to study ice storms and how they work.
In the winters of 2015-16 and 2016-17, researchers at the 7,800-acre Hubbard Brook Experimental Forest in New Hampshire’s White Mountains created the first man-made ice storms, using fire hoses to spray trees with water on freezing nights.
What the research team found was that at a quarterinch of ice or less, trees suffered minimal damage. At a half-inch or more, the branches started falling.
The team estimated that a heavy ice storm could bring down a year’s worth of woody debris in one night. The trees also suffered wounds that did not heal readily. Where icing was heaviest, the damage opened the forest canopy, letting more light onto the forest floor.
Lindsey Rustad, a research ecologist with the U.S. Forest Service, who led the ice storm research at Hubbard Brook said that with climate change making extreme weather events more frequent, it’s important to better understand how ice storms work.
“They happen from Texas to New England to Oregon’’ she said. “They happen all over the world.’’