Tuesday, July 27, 2010

Winter 2010 Rewind: El Niño, NAO Convergence

This past winter was for many, absolutely epic! The rarest of events for big east coast cities unfolded between December and March, blanketing locations from Washington, DC to New York with record snowfall in the form of fierce blizzards and historic nor'easters.

As winter 2010 concluded I conducted two interviews with seasoned meteorologists having expertise in not only northeastern United States weather, but with nor'easters such as those that plowed through in months prior. In both my interviews with winter weather authority, Paul Kocin; and chief forecaster for AccuWeather, Elliot Abrams; the anomalies of two unique weather patterns converging was mentioned as the likely cause of that winter's wrath. Those anomalies were El Niño, the cyclic warming of the tropical Pacific, and the strong negative phase in a pressure cycle called the North Atlantic Oscillation (NAO).

Well alas... this week a new study appearing in the journal, Geophysical Research Letters, states that these two weather patterns did indeed converge along the east coast and are both responsible for the historic winter that unfolded. The study was conducted by a team of scientists at Columbia University's Lamont-Doherty Earth Observatory who analyzed 60 years of snowfall measurements to conclude that the negative NAO this particular winter made the air colder over the eastern United States, causing more precipitation to fall as snow. El Niño brought even more precipitation to the area, which when interacting with the NAO's presence, led to even more snow.

The last time the NAO experienced a strong negative phase was in the winter of 1995-1996. During that winter the east coast was also hammered with above average snowfall. This winter, the NAO was even more negative – a state that happens less than 1 percent of the time.

It is important to note, however, that while the heavy snow on the east coast dominated headlines this winter, the Great Lakes and western Canada (remember this?) actually saw less snow than usual
typical for an El Niño year. The arctic also experienced warmer weather than usual.

Finally, I'd like to once again showcase this radar rewind, courtesy of AccuWeather.com. You will see 22 major storms that doused the northeast in a four month radar animation from December 1 through March 30. AMAZING!

* Note: This video is best viewed in Firefox, Chrome, Safari or any web browser other than Explorer (go figure) and it's totally worth launching those browsers if you have one of them, because this is just awesomeness!

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