How Things Work: Nor'easters

Nor’easters, large weather systems that typically move up the East Coast, drop large amounts of precipitation. (credit: Courtesy of Wikimedia Commons) Nor’easters, large weather systems that typically move up the East Coast, drop large amounts of precipitation. (credit: Courtesy of Wikimedia Commons) Credit: Juan Fernandez/Staff Credit: Juan Fernandez/Staff

The recent threat of heavy snow may seem like odd weather for late April. Although the prediction of snow in Pittsburgh fell through, more than two feet of snow fell about 70 miles away in Laurel Summit, Pa., according to The Washington Post. The culprit? A weather system called a nor’easter, a type of storm that typically passes through the East Coast and quickly drops large amounts of rain and snow.

Nor’easters generally occur where moisture and cold air are abundant. They are cyclones that resemble hurricanes and create hurricane-level winds. In coastal regions, the winds generate huge surfs that can result in beach erosion, cause coastal flooding, and make surfers wait in anticipation.

Nor’easters get their name from the direction of their winds. According to, “A nor’easter is named for the winds that blow in from the northeast and drive the storm up the East Coast along the Gulf Stream, a band of warm water that lies off the Atlantic coast.”

A nor’easter begins its life as a low pressure air system with counterclockwise winds; this can be found in the Gulf coast winds that start off the coast of Florida. The system circulates along the coast from Florida and moves upward, essentially being pushed by the Gulf Stream, gaining warm air and moisture from the Atlantic Ocean as heavy northeastern winds push the system up the East Coast.

Another key element in the formation of a nor’easter is a high pressure system with winds that move cold air down from the Arctic. The winds of the nor’easter collide with the cold Arctic winds, and since cold air is heavier than warm air, the cold air acts as a wedge and causes the warm moist air to rise and form precipitation like rain and snow.

During East Coast winters, nor’easters are quite common. However, only some have the momentum to generate enough precipitation and wind to cause problems on land. The converging point of the low pressure and high pressure systems is the location where the most heavy precipitation and snowfall occur, lessening as one moves further away.

There are two general types of nor’easters. Offshore-forming nor’easters refer to storms that move east from the East Coast. They result in heavy snowfall and precipitation and eventually get blown off the East Coast from the Canadian jet stream up north. Onshore-forming nor’easters move west from the East Coast, resulting in large amounts of rain and winds but not as heavy as those in offshore-forming nor’easters.

During a nor’easter, thick, dark, low-level clouds often block out the sun. Even after the storm passes, the dark clouds linger for several days. Temperatures fall significantly due to the cool air from the northeastern winds. During the storm, all types of precipitation can occur, including rain, snow, and hail. The high wind gusts can also reach hurricane level and even gain a small eye, much like that of a hurricane.

Depending on the severity of the storm, airports, major highways, and interstates often get shut down for a few days. Power failures often occur as electrical wiring gets disrupted due to high winds, ice, and snow.

In the U.S., the area from Virginia to the New England coast, Quebec, and Atlantic Canada are prone to nor’easters, which often occur in the winter and early spring. Although the season matters for the formation of the cold core of a nor’easter, more important are the right conditions, namely the high and low pressure collision.