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What is a Nor’easter? East Coast Braces for Winter Storm Stella

3 minute read

A winter storm this week could bring more than a foot of snow to parts of the Northeast — in other words, a nor’easter.

According to the National Weather Service, a nor’easter is a storm that affects North America’s East Coast, nearly always bringing heavy rain or snow as well as gale-force winds directed from the northeast. As the name suggests, nor’easters typically move toward the northeast as they develop, often reaching peak intensity near New England and Canada’s Maritime Provinces.

Winter Storm Stella: See Photos of the Blizzard That’s Paralyzed the East Coast

A man walks in Central Park as snow falls in Manhattan, New York
A man walks in Central Park as snow falls in New York City, on March 14, 2017. Andrew Kelly—Reuters
Winter Weather New York City
Two men play golf with a tennis ball as Winter Storm Stella sweeps through Times Square in New York City, on March 14, 2017.Mark Lennihan—AP
Times Square Public Safety Sergeant Baldwin Davis captures falling snow with his cellular device in Times Square in Manhattan, New York
Times Square Public Safety Sergeant Baldwin Davis captures falling snow with his phone in Times Square in New York City, on March 14, 2017. Andrew Kelly—Reuters
Workers clear steps in Times Square as snow falls in Manhattan, New York
Workers clear steps in Times Square as snow falls in New York City, on March 14, 2017. Andrew Kelly—Reuters
Major Blizzard Hammers East Coast With High Winds And Heavy Snow
The 'Fearless Girl' statue stands in the snow in New York City's Financial District, on March 14, 2017.Drew Angerer—Getty Images
Winter Weather New York
A pedestrian crosses a street during Winter Storm Stella in New York City, on March 14, 2017.Mary Altaffer—AP
Major Blizzard Hammers East Coast With High Winds And Heavy Snow
The information board in Terminal C at Logan International Airport shows the majority of flights cancelled during Winter Storm Stella in Boston, on March 14, 2017.Scott Eisen—Getty Images
Major Blizzard Hammers East Coast With High Winds And Heavy Snow
Terminal C at Logan International Airport is nearly empty during Winter Storm Stella in Boston, on March 14, 2017.Scott Eisen—Getty Images
Snowplows clear the runway of snow at LaGuardia Airport in New York
Snowplows clear the runway of snow at LaGuardia Airport in New York City, on March 14, 2017. Shannon Stapleton—Reuters
Tourists Jake Lambert, Clay Lambert and Kelsey Chaloux from Orlando, Florida play snowball on Capitol Hill in Washington
Tourists Jake Lambert, Clay Lambert and Kelsey Chaloux from Orlando, Fla. play snowball on Capitol Hill in Washington, D.C., on March 14, 2017. Yuri Gripas—Reuters
US-WEATHER-STORM-STELLA
The Washington Monument is seen behind the snow-covered Mall in Washington, D.C., on March 14, 2017.Mandel Ngan—AFP/Getty Images
Major Blizzard Hammers East Coast With High Winds And Heavy Snow
Ice covers cherry blossoms near the Jefferson Memorial in Washington, D.C., on March 14, 2017.Win McNamee—Getty Images
Major Blizzard Hammers East Coast With High Winds And Heavy Snow
A U.S. Park Service worker shovels snow off of the sidewalk at the White House in Washington, D.C., on March 14, 2017.Mark Wilson—Getty Images
Winter Weather Philadelphia
A couple walks in the street during Winter Storm Stella in Philadelphia, on March 14, 2017.Matt Rourke—AP

Nor’easters — which occur most frequently between September and April — are fueled by warm air over coastal waters from the Gulf Stream meeting cold air over East Coast land, a product of the polar jet stream.

By comparison, a winter storm is a more generic term for a weather system that produces snow, sleet, freezing rain or a “wintry mix.” Unlike a nor’easter, it can occur anywhere across the country — as can blizzards. But blizzards must also meet a set of specific criteria: at least three consecutive hours of “considerable” falling or blowing snow as well as sustained winds of 35 miles per hour or greater.

The National Weather Service has issued a blizzard warning for New York City and parts of New Jersey and Connecticut, predicting 12 to 20 inches of snowfall between Monday night and Tuesday night. Winter storm warnings and watches have also been issued throughout other parts of the Northeast.

“This is a classic nor’easter,” said Jim Hayes, a meteorologist at the Weather Prediction Center. “From a strictly meteorological perspective, it’s an intensifying mid-latitude cyclone, but nobody cares about that.” He said only meteorologists would describe it that way. Nor’easter is the more colloquial term.

“Anybody who lives north of North Carolina understands what a nor’easter is,” he said.

Hayes said the concept of a nor’easter can be traced back to Benjamin Franklin in the 1700s. Franklin had hoped to watch a lunar eclipse from Philadelphia in 1743, but a storm moved in, and clouds blocked his view. He assumed his brother in Boston, to the northeast, would have fallen victim to the storm first and would also have been unable to see the eclipse. But he later learned that wasn’t the case; his brother saw the lunar eclipse before the storm reached Boston. While the winds were blowing from the northeast, the storm was moving from the southwest, enabling Franklin to conclude that storms can move in a direction opposite their winds — as nor’easters do.

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Write to Katie Reilly at Katie.Reilly@time.com