Image Courtesy: Anirudh Koul

What is a 'Nor'Easter'?

By Sam Dunaiski @yourmetsam February 24, 2015 1:52 am CST

Over the past few years, the general public has become quite familiar with some very specific meteorological terms. The Polar Vortex, Alberta Clipper, and El Nino are now fairly well-known even among non-meteorologists. Depending on one's location, knowledge of these specific terms changes. Folks in the Plains know about Panhandle Hooks, while Midwesterners are all too familiar with Clipper systems. Along the Atlantic coast, residents often fear the nor'easter.


In simple terms, a nor'easter is a large cyclone (low pressure system) that moves up the east coast. They typically occur between fall and spring, but can develop at any time of year. Part of what makes nor'easters so dangerous (and well known) is the fact that they strike along the densely populated northeast corridor from Washington D.C. to Boston. But what really separates a nor'easter from any garden variety low pressure system? Quite a few things, in fact.


Moving image of a nor'easter, or major storm sytem.

Ideal Nor'easter from NOAA.


Like any storm complex, a nor'easter requires moisture and a contrast of warm and cold air. As it turns out, the typical pattern of a nor'easter is uniquely geared to maximize these variables. Usually originating in the southeast U.S., these lows already have two abundant sources of moisture: the Gulf of Mexico and the Atlantic Ocean. These moisture sources are both relatively warm. An ideal nor'easter setup will also have colder/drier air to the north, typically over the Great Lakes. Sometimes, these storms will not fully intensify until they reach the New England states, where colder/drier air masses are more likely to be found. This is largely due to the winter location of the polar jet stream, often located along the U.S./Canadian border.


Nor'easters can bring a wide variety of precipitation types, depending on the location. Rain will typically fall in the southern portions of the storm, but further north, sleet and freezing will often mix into many areas. Some of the worst ice-storms in the eastern U.S. are due to nor'easters. In the far northern and western quadrants of the cyclone, heavy snow is usually the result. In fact, the largest snowfalls ever in New York, Boston, Baltimore, and Washington D.C. are all due to nor'easters.



(Brooklyn Bridge from NBC News)


The precipitation that comes with nor'easters is often crippling to the region, but perhaps the most notable characteristic of these storms is the wind. In fact, the strong northeast winds are the very reason nor'easters get their name. The inward/counter-clockwise flow around these lows pull in warm/moist air from the Atlantic Ocean as they move up the coast. The winds strengthen as the temperature difference between the cold air over land and the (relatively) warm air over the ocean increases. These strong winds can do everything from downing trees and power lines to creating blizzard/whiteout conditions.


Nor'easters can be dangerous, multi-day events, but thankfully, computer models often handle these systems rather well. With reasonable planning, most areas can adequately plan for the effects these storms can bring to the region.


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