Nor'easter

A nor'easter (also northeaster; see below) is a macro-scale cyclone. The name derives from the direction of the strongest winds—as an offshore air mass rotates counterclockwise, winds tend to blow northeast-to-southwest over the region covered by the northwest quadrant of the cyclone. Use of the term in North America is associated with several different types of storms, some of which can form in the North Atlantic Ocean and some of which form as far south as the Gulf of Mexico. The term is most often used in the coastal areas of New England and the Mid-Atlantic states. Typically, such storms originate as a low-pressure area that forms within 100 miles (160 km) of the shore between Georgia and New Jersey. The precipitation pattern is similar to that of other extratropical storms. Nor’easters are usually accompanied by very heavy rain or snow, and can cause severe coastal flooding, coastal erosion, hurricane-force winds, or blizzard conditions. Nor'easters are usually most intense during winter in the Mid-Atlantic, New England, and Canadian Maritimes. They thrive on converging air masses—the cold polar air mass and the warmer air over the water—and are more severe in winter when the difference in temperature between these air masses is greater.

Nor'easters tend to develop most often and most powerfully between the months of September and April, although they can (less commonly) develop during other parts of the year as well. The Northeast megalopolis is very heavily affected by Nor'easters each winter, as the East Coast of the United States is a prime spot for these storms to develop, where warm air from the Atlantic Ocean collides with the arctic cold to the north and west.

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