A Northeaster, or Nor’easter, is a very large storm system that occurs along the eastern coast of the United States between the months of October and April. These storms generate large amounts of precipitation and high winds, which can cause structural damage.
First, we must look at the regular weather conditions on the East Coast. A usual storm begins life in the Gulf Stream in Florida, where the warm waters evaporate and create a low-pressure area. This system is then moved up the Eastern Seaboard by the northeasterly winds in the area. While this storm builds force off the coast, it hits a cold front descending from Canada. The difference between the cold front and the warm humidity forces the clouds to drop the moisture in the form of rain, sleet, or snow, depending on the prevalent air temperature. Eventually, the storm will be whisked out to sea, to eventually pester the residents of Western Europe. That, however, is another node.
While these weather conditions are normal throughout the year, occasionally a storm system will become very strong before moving to the northeast. And during the winter months, difference in temperature between the cold front and the low-pressure system can be extreme. These storms generate blizzards that bring down feet worth of snow, causing power lines to snap, roofs to collapse, and entire cities to shut down for days at a time.
Large Northeasters are usually the stuff of legend along the Atlantic coast. In April of 1962, a Northeaster sat off the coast for five days, actually changing the contour of the Atlantic coastline from North Carolina to Nova Scotia. In 1993, a Northeaster destroyed property along the coast, cause over $1 billion in damages and leaving many families homeless. Most recently, a Northeaster came through in December of 2003, killing several people and leaving over 40" of snow in some areas.