Nor'easters will usually develop between 30 N. and 35 N.
The sharp contrast in the cold Labrador current and the warm Gulf Stream, as well as the topographic nature of the Northeast, make the Mid-Atlantic and New England coast one of the most conducive areas in the world for nor'easter formation. It is thought that nor'easters are caused by the Arctic oscillation, which is a band of air circulating at about 55°N. The Arctic oscillation has two phases: positive and negative. In the positive phase, the predominant phase for the past twenty years, the air moves quickly and acts almost like a dam in preventing the intrusion of Arctic air into the mid-latitude regions. In its negative phase, the air moves more slowly and is more subject to disruption. This allows cold Arctic air to penetrate into the mid-latitudes. There can be a fluctuation between positive phase and negative phase days over the course of a winter, and a correlation between negative phase days and nor'easters has been found.
Most Nor'easters start from a low-pressure system that forms in the south, most often the Gulf of Mexico, and are drawn across to the Northeast by the Jet Stream. The divergence or diffluence in the upper atmosphere caused by the Jet Stream removes and disperses the rising air at a faster rate than it is replaced at the surface, which, along with the Coriolis Effect, creates and develops a storm. Their northeast track brings them up along the East Coast past the mid-Atlantic and New England coastal states. The counterclockwise flow around a low pressure system brings the warm moist oceanic air over land. The warm moist air meets cold air carried southward by the trough. The deepening low enhances the surrounding pressure gradient, which acts to spiral the very different air masses toward each other at an even faster rate. The greater the temperature differences between the two air masses, the greater the turbulence and instability, and the more severe the storm can become. .
If the nor'easter takes the East Coast track, that usually indicates the presence of a high pressure area in the vicinity of Bermuda. The storm will then reach the North Carolina coast and begin to develop. At this time, the nor'easter can move slightly offshore, which would be the more destructive path, or, it can move slightly inland, which would present mostly rain. If it takes the offshore path, it would begin to rapidly strengthen. Now, the effects would start reaching the major cities of the Northeast, such as New York City. The storm, now rapidly intensifying, tracks northward. These storms sometimes intensify during their entire existence. The storm moves northward, following the topography of the East Coast. It usually reaches its peak intensity while off the Canadian coast. The storm then reaches Arctic areas, and can reach intensities equal to a strong hurricane. They then meander throughout the North Atlantic and can last for several weeks.
Until the nor'easter passes, thick, dark, low-level clouds often block out the sun. During a single storm, the precipitation can range from a torrential downpour to a fine mist. Low temperatures and high wind gusts are also associated with a nor'easter. On very rare occasions, such as in the North American blizzard of 2006 and a nor'easter in 1979, the center of the storm can take on the circular shape more typical of a hurricane and have a small eye. All precipitation types can occur in a nor'easter, although they are well-known for their frozen precipitation.
The Atlantic coast, from northern Georgia northward up the coast, can suffer high winds, pounding surf, and extremely heavy rains during these storms. However, swells have been known to cause damage through the Caribbean as well. Surfers wait in anticipation when a nor'easter is formed. Nor'easters cause a significant amount of severe beach erosion in these areas, as well as flooding in the associated low-lying areas. Beach residents in these areas may actually fear the repeated depredations of nor'easters over those of hurricanes, because nor'easters happen more frequently and cause substantial damage to beach-front property and their dunes. Nor'easters are often mistaken for Transwiki:Euroclydons, but these are two separate weather patterns. A Euroclydon is a tempestuous northeast wind that blows in the Mediterranean.
As noted in a January 2006 editorial by William Sisson, editor of Soundings magazine, use of "nor'easter" to describe the storm system is common along the U.S. East Coast. Yet, it has been asserted by linguist Mark Liberman (see below) that "nor'easter" as a contraction for "northeaster" has no basis in regional New England dialect and is a "fake" word, which is a parochial view that neglects the little-known etymology and the historical maritime usage described above.
Nineteenth century Downeast mariners pronounced the compass point "north northeast" as "no'nuth-east," and so on. For decades, Edgar Comee, of Brunswick, Maine, waged a determined battle against use of the term "nor’easter" by the press, which usage he considered “a pretentious and altogether lamentable affectation” and "the odious, even loathsome, practice of landlubbers who would be seen as salty as the sea itself." His efforts, which included mailing hundreds of postcards, were profiled, just before his death at the age of 88, in The New Yorker.
Despite the efforts of Comee and others, use of the term continues by the press. According to Boston Globe writer Jan Freeman, "from 1975 to 1980, journalists used the nor'easter spelling only once in five mentions of such storms; in the past year (2003), more than 80 percent of northeasters were spelled nor'easter.
University of Pennsylvania linguistics professor Mark Liberman has pointed out that while the OED cites examples dating back to 1837, they represent the contributions of a handful of non-New England poets and writers. Liberman posits that "nor’easter" may have originally been a literary affectation, akin to "e'en" for "even" and "th'only" for "the only," which is an indication in spelling that two syllables count for only one position in metered verse, with no implications for actual pronunciation.