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Posted at 06:41 PM ET, 12/05/2011

The Arctic Oscillation, going to extremes

The Arctic Oscillation in December 2009, 2010, and, thus far, in 2011. (NOAA Climate Prediction Center)
Wondering why it’s been so warm the last couple of weeks? Check out the behavior of the Arctic Oscillation (AO, to the right). It’s been highly positive, meaning cold air has been bottled up at high latitudes.

Compare that to 2009 and 2010, when it was highly negative, and Arctic air plunged into the eastern U.S. setting the stage for 2009’s Snowpocalypse and the big December 26 snowstorm that crushed the coast, while just grazing D.C.

Wes Junker wrote last week that this year’s positive AO pattern is not favorable for big snows (or persistent cold air outbreaks) so far. But as he wrote earlier today, smaller snow events could still materialize under the right circumstances which may set up Thursday morning...

[Image hat tip, Weather Channel meteorologist Stu Ostro (via Twitter)]

By  |  06:41 PM ET, 12/05/2011

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