Ask the Weather Guys: What is a nor’easter?

2012-11-11T15:30:00Z Ask the Weather Guys: What is a nor’easter?STEVEN A. ACKERMAN and JONATHAN MARTIN | UW-Madison department of atmospheric and oceanic sciences madison.com

Q: What is a nor’easter?

A: A nor’easter is an extratropical cyclone that affects the northeastern United States and extreme eastern Canada. An extratropical cyclone is a low-pressure system that forms outside of the tropics and is usually associated with fronts, unlike a tropical cyclone. A nor’easter is named for the strong northeasterly winds that blow across this region as the path of the low pressure moves northeastward, slightly to the east of the North American coastline.

The counterclockwise winds that flow around the low pressure system draw moist maritime air from over the Atlantic Ocean. At the same time, cold polar air from Canada air moves southward toward the East Coast and encounters northward-moving warmer and more humid air originally from the Gulf of Mexico. The dynamics of the resulting warm and cold fronts produces some of the heaviest snowfalls that occur along the East Coast.

Nor’easters often occur between the months of October and April, but are particularly dangerous during winter months, when cold weather-related deaths occur due to exposure to cold air and loss of power due to high winds, ice, and snow. Nor’easters also can cause coastal flooding, coastal erosion and strong winds.

The nor’easter of Halloween 2011 was accompanied by record-breaking snowfall across New England and killed 39 people. The Presidents’ Day Weekend, February 15-17, 2003, was a nor’easter that dumped record snowfall in many areas along the East Coast. It claimed the lives of 42 people nationwide and stranded thousands of travelers. Perhaps the most notorious nor’easter is the Great Blizzard of 1888 which dropped 4 feet of snow in New York and killed 400 people.

Steve Ackerman and Jonathan Martin, professors in the UW-Madison department of atmospheric and oceanic sciences, are guests on WHA radio (970 AM) at 11:45 a.m. the last Monday of each month.

Copyright 2015 madison.com. All rights reserved. This material may not be published, broadcast, rewritten or redistributed.

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