Though tornadoes and hurricanes are well known for their destructive force, few people understand the deadly nature of the nor'easter. Named for the counterclockwise direction of wind flow around an area of low pressure, these storms are capable of bringing high winds, heavy precipitation and strong wave action to the eastern seaboard of the United States.
Low Pressure Forms
Ben Franklin was the first to notice that northeast winds usually followed precipitation that began in the south and moved northward up the coast. This is the typical pattern of the nor'easter. According to Robert E. Davis in his article "Nor'easter", written in Volume 81 of the American Scientist, nor'easters begin life like all storms, arising from an unstable atmosphere. This instability is often the result of frontal activity, where a cooler air mass meets the face of a warmer air mass, and the difference in temperature causes the atmosphere to destabilize. The resulting area of low pressure is nature's way of trying to stabilize an unstable situation.
According to Davis, a nor'easter also needs the presence of a strong jet stream to develop. The jet stream acts as a catalyst by moving mass away from the heart of the low pressure system, causing surface pressure to drop. This results in an intensifying low. When driven by prevailing west winds out over the Atlantic, a nor'easter can develop.
The Storm Track
Once a low pressure area has been driven over the Atlantic, it moves northward following the coastline. The exact track determines the effects it has on the land. If the low stays over water, the clockwise rotation of the storm brings the warmer air off the ocean onto shore. Here it meets with colder air. The low acts like a blender, spinning warm and cold air and becoming stronger. This causes high winds which bring about strong wave action. Moisture from the ocean feeds the storm, falling mostly in the form of snow or ice. When the low tracks farther inland, the effects of the storm are usually less severe, with decreased amounts of precipitation and less of a storm surge.
Nor'easters continue to follow the coastline toward Maine and the Canadian Maritimes. As they exit an area, strong winds on the back of the storm hit the region from the north and east, giving the storm its name. These winds can be heavy and sustained, causing blowing and drifting snow, wide spread wind damage and power outages.
Worst Nor'easter storms
The largest number of nor'easter storms recorded occurred between the 1940's and the 1960's. According to Davis, the jet stream is now running in a more northerly location than it once was. In the 20 year period prior to 1960, at least 35 storms a year were recorded. Since then, the number of yearly storms has decreased, but significant storms have happened. One of these occurred in 2003. A nor'easter low moving northward from the Carolinas joined forces with a low exiting the Midwest near Washington D.C. Known as the President's Day Storm of 2003, it brought 15 to 30 inches of snow to cities from Boston to D.C.
Possibly the worst nor'easter in recorded history happened in March of 1968 and has become known as the Ash Wednesday storm. According to the U.S. Geological Survey, it was one of the worst storms to hit the mid-Atlantic states and still ranks as one of the ten worst storms of the 20th century. Low pressure stalled for three days over the Atlantic ocean causing snow to fall as far south as Alabama. Blizzard conditions were reported in North Carolina. Farther north, at Ocean City, Maryland, 60 mile per hour winds were recorded with 25 foot waves. In Rehoboth Beach, Delaware, 40 foot waves destroyed homes and flattened sand dunes. On Long Island, entire communities were destroyed.
Some of the worst storms in recorded history have been nor'easters.They are common in the winter months due to the southern position of the jet stream and the associated frontal action. Because it is isolated to the eastern seaboard of the U.S., this storm is not as well known as hurricanes and tornadoes, but is capable of causing widespread damage, through snow, strong winds and high wave action.