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Blame jet stream, Arctic air for repeat snowstorms

Quincy firefighters shoveled out a hydrant on Sea Street.
Quincy firefighters shoveled out a hydrant on Sea Street.(David L. Ryan/Globe Staff)

We have broken the record for most snow received within two weeks. And within a 30-day period. The 40-day record? Shattered.

So forgive us if we shake our fists at the sky and wail “Why us?” as we prepare for a bit more snow on Thursday — with early inklings of some sort of weekend event.

Meteorologists say the state keeps getting hit by snowstorm after snowstorm after snowstorm because of a simple weather pattern: The position of the jet stream combined with the extreme cold air that has come down from the Arctic into eastern Canada turns out to be the perfect setup for endless shoveling.

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“We have to realize that prior to January 23, we had almost no snow and most people were saying, ‘Ah, it’s a nothing winter, no snow on the ground, nothing to worry about,’ ” said Harvey Leonard, chief meteorologist for WCVB. “Sometimes in the world of meteorology it doesn’t take that big of a shift to create dramatic changes in your weather.”

That shift was a slight curve in the jet stream that began to ferry storms on the right track to deliver knock-out punches, instead of glancing blows.

“This winter is a combination of the cold temperatures being low enough that every storm is snow as opposed to any of them having rain. . . . And the storms are primarily coastal storms, meaning they get lots of moisture from the ocean,” said Don McCasland, program director of Blue Hill Meteorological Observatory.

Typically, the ratio between moisture and snow is about 1 to 10 in Eastern Massachusetts. That means every inch of precipitation equals about 10 inches of snow. This year, that ratio has been snowier than usual. For every inch of precipitation, storms have dumped somewhere around 15 or even 20 inches of snow in Eastern Massachusetts, McCasland said.

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Ironically, McCasland said, what is helping keep things cold is not only the weather patterns, but also the snow itself.

With snow covering practically everything, much of the heat from the sun is being reflected back into space, instead of being absorbed by the ground and helping warm things up.

But cold alone does not bring snowfall records. A deviation in the jet stream, which flows from west to east across the country, has put New England in what meteorologists call a “trough.”

The jet stream can deviate north or south on its way eastward, and one way to envision what’s happening is to think of it normally taking a path from Denver to Virginia and then flowing out east, over the ocean, Leonard said. In that scenario, the storms don’t get too close to us. But if the jet stream swings northeast, it’s perfectly positioned to bring the storms to our doorstep.

Those storms swirl in a counter-clockwise direction, bringing moisture from the ocean. That combines powerfully with the cold air to the northwest, which swirls in the opposite direction and brings northeast winds.

“The moisture and the cold — that’s the magic combination for us,” Leonard said.

While no individual weather event is indicative of climate change, Paul O’Gorman, an atmospheric scientist at the Massachusetts Institute of Technology has found evidence that a warming climate will decrease overall snowfall each winter but increase the intensity of extreme events.

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Unfortunately for those who do not relish winter and snowstorms, meteorologists do not see much sign of change in the immediate future.

Asked when the pattern will shift, Stephanie Dunten, a National Weather Service meteorologist in Taunton, simply said, “We would like it to.”

Leonard ventured that the bitter cold of this weekend, lasting into Monday, might be the harshest — though not the end — of the cold for the season.

“There are no immediate indicators of warming in the near future,” McCasland said. “But the bottom line is it is going to warm up. Spring will come. Maybe not until July, but it will come.”


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