What Exactly Is a Nor’easter?

The East coast is readying itself for heavy snow, strong winds, and blizzard conditions this week from the New York City metro area up into the Boston metro area, with snow as far south as Washington, D.C.  This storm will likely cause dangerous travel conditions, power outages, and coastal flooding.

March 2014 Nor'easter

March 2014 Nor’easter. Credit: NOAA.

A nor’easter is a cyclonic storm that moves along the east coast of North America. It’s called “nor’easter” because the winds over coastal areas blow from a northeasterly direction. It is defined as NOAA as a strong low pressure system that affects the Mid Atlantic and New England States. It can form over land or over the coastal waters. These winter weather events are notorious for producing heavy snow, rain, and tremendous waves that crash onto Atlantic beaches, often causing beach erosion and structural damage. Wind gusts associated with these storms can exceed hurricane force in intensity. A nor’easter gets its name from the continuously strong northeasterly winds blowing in from the ocean ahead of the storm and over the coastal areas.

Nor’easters may occur any time of the year, but are most frequent and strongest between September and April. These storms usually develop between Georgia and New Jersey within 100 miles of the coastline and generally move north or northeastward.

Nor’easters typically become most intense near New England and the Canadian Maritime Provinces. In addition to heavy snow and rain, nor’easters can bring gale force winds greater than 58 miles per hour. These storms can produce rough seas, coastal flooding and beach erosion.

The East Coast of North America provides an ideal breeding ground for nor’easters.  During winter, the polar jet stream transports cold Arctic air southward across the plains of Canada and the U.S., and eastward toward the Atlantic Ocean, as warm air from the Gulf of Mexico and the Atlantic tries to move northward. The warm waters of the Gulf Stream help keep the coastal waters relatively mild during the winter, which in turn helps warm the cold winter air over the water. This difference in temperature between the warm air over the water and cold Arctic air over the land is the area where nor’easters are born.

This animation of NOAA GOES-13 satellite imagery from March 5 to March 7, 2013, shows the progression of a cold front from the west associated with a low pressure system that brought snow from Chicago to the Appalachian Mountains. The low merged with a coastal low near the Mid-Atlantic on March 6 and brought more than 18″ of snow from western north Virginia and western Maryland into Pennsylvania, while coastal areas and cities including Washington, D.C. and Baltimore received snow followed by heavy rain. The low is affecting New England on March 7. Credit: NASA GOES Project.

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