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Science behind the storm: Atmospheric blend for a behemoth

Light snow fell in Copley Square Monday afternoon.
Light snow fell in Copley Square Monday afternoon.(Darren McCollester/Getty Images)

The storm that rolled in Monday night was the kind meteorologists live for all year.

Cold arctic air crept southward starting the night before. A high pressure system anchored over eastern Canada stirred up a cold northeasterly wind. A storm swept across the country, leaving moderate snow in its wake in the Midwest.

And then, on Monday, a low pressure center began to churn up from the Outer Banks of North Carolina, picking up moisture from the Atlantic Ocean.

This confluence of cold air, moisture, and high and low pressure systems was perfectly positioned to create snow and wind — lots of it. Meteorologists said the storm would undergo “bombogenesis,” when the barometric pressure drops extremely rapidly and causes the storm to intensify.

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It is expected to move slowly, likely creating 36 hours of snowfall.

“It’s symmetry in motion, to make it a classic nor’easter,” said Kim Buttrick, a meteorologist at the National Weather Service in Taunton. “This is what a lot of meteorologists look for every year. For people who love winter, these are the ingredients they look for; this is what makes their heart race. They get very excited.”

Many storms have just one of the elements that were in place Monday evening, or are positioned in such a way that they pass by quickly. But not the predicted blizzard of 2015.

“You’ve got all the elements coming together in just the right way that produces a classic, major nor’easter for southern New England,” said Harvey Leonard, a meteorologist at WCVB-TV. “This is part of our history. These storms occur.’’

This storm bears some similarities to the February blizzard of 2013, which produced more than 24 inches of snow in Boston, caused major coastal flooding, and is ranked as one of the five biggest storms for the city.

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Leonard and other meteorologists are careful not to prejudge a storm, but many thought the setup was right for a blizzard that could make it into the top 10 biggest storms in the record books.

Matt Noyes, chief meteorologist at NECN, said that when he and Leonard gave presentations on two top-five blizzards at a weather conference, they noticed an interesting difference in how the two storms were driven. Leonard talked about the Blizzard of ’78 and Noyes the February blizzard of 2013.

The 1978 blizzard, Noyes said, seemed to get a bigger contribution from cold Arctic energy.

“A lot of our modern-day blizzards are being driven by subtropical moisture — warm, moist input, which is getting the job done because we have enough cold air in place to make it snow,” Noyes said. “It is different from some of the classic blizzards” of many years ago.

As the powerful storm barreled toward the region Monday, meteorologists were not worrying about whether it would hit or miss some areas. Instead, they were trying to divine just how much snow would fall. They expected bands of heavier precipitation at times, which are harder to predict, but there was not much uncertainty over whether there will be a lot of snow.

“It’s not going to miss,” Leonard said. “Someone may say it wasn’t as bad as I was anticipating, or it’s worse than they described. That’s your range.”

At the Blue Hill Meteorological Observatory in Milton, chief observer Brian Fitzgerald went to work with an inflatable mattress, sleeping bag, snowshoes, skis, and his Alaskan husky — a retired sled dog named Pearl. He pulled out the record books and was examining the observers’ notes from the Blizzard of 1978 as he prepared to spend two nights holed up tracking the storm.

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“Depending on your opinion, fortunately or unfortunately, it’s the perfect setup for a perfect winter event with all snow everywhere,” Fitzgerald said. “You need a very good coincidence like we’re having here.”


Carolyn Y. Johnson can be reached at cjohnson@globe.com. Follow her on Twitter @carolynyjohnson.