Editing Nor'easter (section)

==Geography and formation characteristics==

[[File:Gulf Stream water temperature.jpg|thumb|upright=.90|Surface temperature of the sea off the east coast of North America. The corridor in yellow gives the position of the Gulf Stream.]]

===Formation===
Nor'easters develop in response to the sharp contrast in the warm [[Gulf Stream]] ocean current coming up from the tropical Atlantic and the cold air masses coming down from Canada. Very cold and dry air rushing southward and meeting up with the warm Gulf stream current, which is typically  near {{convert|70|F|C}} even mid-winter, often causes [[low-pressure area]]s to develop and intensify.

In the [[upper atmosphere]], the strong winds of the [[jet stream]] remove and replace rising air from the Atlantic more rapidly than the Atlantic air is replaced at lower levels; this and the [[Coriolis force]] help develop a strong storm. The storm tracks northeast along the East Coast, normally from North Carolina to Long Island, then tracks east toward the waters off [[Cape Cod]]. Counterclockwise winds around the [[low-pressure system]] blow the moist air over land. The relatively warm, moist air meets cold air coming southward from Canada. The low increases the surrounding pressure difference, which causes the very different air masses to collide at a faster speed. When the difference in temperature of the air masses is larger, so is the storm's instability, turbulence, and thus severity.<ref name=autogenerated1/><ref name="disc1">{{cite web|author=Storm-E|title=Nor'easters|year=2007|access-date=January 22, 2008|url=http://www3.cet.edu/weather2/h17.html|url-status=dead|archive-url=https://web.archive.org/web/20070626044252/http://www3.cet.edu/weather2/h17.html|archive-date=June 26, 2007|df=mdy-all}}</ref>

The nor'easters taking the East Coast track usually indicates the presence of a [[High pressure|high-pressure]] area in the vicinity of [[Nova Scotia]].<ref name="disc4">{{cite web|author = The Weather Channel|title = Nor'easters|year = 2007|publisher = [[The Weather Channel]]|access-date = January 24, 2016|url = http://dw.weather.com/encyclopedia/winter/noreast.html|url-status = dead|archive-url = https://web.archive.org/web/20160408114440/http://dw.weather.com/encyclopedia/winter/noreast.html|archive-date = April 8, 2016|df = mdy-all}}</ref> Sometimes a nor'easter will move slightly inland and bring rain to the cities on the coastal plain (New York City, Philadelphia, Baltimore, etc.) and snow in New England (Boston northward). On occasion, nor'easters can pull cold air as far south as Virginia or North Carolina, bringing wet snow inland in those areas for a brief time.<ref name="disc3">{{cite web|author=Multi-Community Environmental Storm Observatory|title=Nor'easters|year=2006|access-date=January 22, 2008 |url=http://www.mcwar.org/articles/noreasters/NorEasters.html |archive-url = https://web.archive.org/web/20071009034304/http://www.mcwar.org/articles/noreasters/NorEasters.html |archive-date = October 9, 2007}}</ref> Such a storm will rapidly intensify, tracking northward and following the topography of the East Coast, sometimes continuing to grow stronger during its entire existence. A nor'easter usually reaches its peak intensity while off the [[Canada|Canadian coast]]. The storm then reaches Arctic areas, and can reach intensities equal to that of a weak [[Tropical cyclone|hurricane]]. It then meanders throughout the [[North Atlantic]] and can last for several weeks.<ref name="disc3"/>

Meteorologists use the [[Miller classification]] to determine the track and severity of a nor'easter. The technique is named after J.E. Miller, who created the system in 1946.<ref name="Weatherworks">{{cite web|title=The Miller Classification|date=December 4, 2020|last=Priante|first=Mike|url=https://weatherworksinc.com/news/Miller-A-vs-Miller-B|publisher=WeatherWorks Inc.|access-date=December 11, 2020}}</ref> The Miller classification classified storms into two categories: type A and type B. Type A storms form in the Gulf of Mexico or along the coast of [[Georgia (US State)|Georgia]] or [[South Carolina]], and cause heavy snow mainly to parts of the inland upper south, Mid-Atlantic, New England, and Atlantic Canada. Type B storms form from a parent low-pressure system over the Ohio Valley, which then undergoes a center reformation over [[Gulf Stream]] off North Carolina or Virginia. These storms can bring a swath of wintry precipitation from the [[Great Plains]] and the [[Ohio River Valley]] to the Middle Atlantic and New England.<ref name="Weatherworks"/><ref name="NWSPA">{{cite report|title=Types of Storms that Typically Produce Heavy Snow in PA|url=https://www.weather.gov/ctp/SnowStormTypes#MillerAMap|publisher=National Weather Service State College, Pennsylvania|access-date=December 11, 2020}}</ref>

===Characteristics===
Nor'easters are usually formed by an area of [[vorticity]] associated with an upper-level disturbance or from a kink in a frontal surface that causes a surface low-pressure area to develop. Such storms are very often formed from the merging of several weaker storms, a "parent storm", and a polar jet stream mixing with the tropical jet stream.

Temperatures usually fall significantly due to the presence of the cooler air from winds that typically come from a northeasterly direction. During a single storm, the precipitation can range from a torrential downpour to a fine mist. All precipitation types can occur in a nor'easter. High wind gusts, which can reach hurricane strength, are also associated with a nor'easter. On very rare occasions, such as in the [[Northeastern United States Blizzard of 1978|nor'easter in 1978]], [[North American blizzard of 2006]], [[Early February 2013 North American blizzard]], and [[January 2018 North American blizzard]], the center of the storm can take on the circular shape more typical of a [[hurricane]] and have a small "dry slot" near the center, which can be mistaken for an [[eye (cyclone)|eye]], although it is not an eye.

====Difference from tropical cyclones====
Often, people mistake nor'easters for [[tropical cyclones]] and do not differentiate between the two weather systems. Nor'easters differ from tropical cyclones in that nor'easters are [[cold-core low|cold-core low-pressure systems]], meaning that they thrive on drastic changes in temperature of Canadian air and warm Atlantic waters.  Tropical cyclones are warm-core low-pressure systems, which means they thrive on purely warm temperatures. However, in rare cases, such as the [[1991 Perfect Storm]], a small tropical cyclone can develop inside the [[warm seclusion]] of an intense nor'easter if the [[sea surface temperature]]s are sufficiently warm. Nor'easters can rarely also turn into tropical or subtropical cyclones, such as [[October 2021 nor'easter|Tropical Storm Wanda]] in 2021.

====Difference from other extratropical storms====
A nor'easter is a strong [[extratropical cyclone]], often experiencing [[explosive cyclogenesis]]. While this formation occurs in many places around the world, nor'easters are unique for their combination of northeast winds and moisture content of the swirling clouds. Nearly similar conditions sometimes occur during winter in the Pacific Northeast (northern Japan and northwards) with winds from NNW. In Europe, similar weather systems with such severity are hardly possible; the moisture content of the clouds is usually not high enough to cause flooding or heavy snow, although northeasterly winds can be strong.

===Geography===
The [[eastern United States]], from [[North Carolina]] to [[Maine]], and [[Eastern Canada]] can experience nor'easters, though most often they affect the areas in the [[ Atlantic Canada]] and [[New England]]. The effects of a nor'easter sometimes bring high surf, strong winds and rain as far south as coastal [[South Carolina]]. Nor'easters cause a significant amount of beach erosion in these areas, as well as flooding in the associated low-lying areas.

Biologists at the [[Woods Hole Oceanographic Institution]] on [[Cape Cod]] have determined nor'easters are an [[Natural environment|environmental]] factor for [[red tide]]s on the Atlantic coast.