NAO 411

I bet everyone has heard of El Nino and La Nina. Perhaps a lesser-known climatic influence is that of the NAO (or North Atlantic Oscillation). The NAO is the fluctuation in pressure of the atmosphere over the Northern portion of theĀ  Atlantic Ocean. positive2This oscillation affects the steering winds of the atmosphere, affecting weather over the northern hemisphere. It was discovered in the early part of the 20th century, making it a relatively new weather term for many! When the NAO is in its positive phase the stormtrack doesn’t bring down the intensely cold air from the Arctic. Instead, it drops into Quebec and the Canadian maritimes. A large subtropical high is set up in the Atlantic which keeps the Southeastern United States warmer than normal.

When the NAO goes into negative phase (which is where it is currently), the subtropical ridge is considerably weaker and pushed a little further to the north (or not even in existence).


The main branch of the jet stream brings the cold, Arctic air down into the Central United States, then down to the Southeast. The only warm spots on the continent are the Canadian maritimes into Greenland.

So, where do we go from here? Here is a look at NOAA’s North Atlantic Oscillation chart. The top chart indicates the observed oscillation (positive is above the 0 line, negative is below) with respect to zero (which is neutral). The lines in red that go to the right are the forecast models for the next few weeks. Notice they remain below zero, but slowly start coming back toward the end of the month. That means that colder than normal temperatures can be expected here through the end of the year with a slow rebound toward Christmas and New Years.


Posted under climate/climate change, cold blast, heat wave

This post was written by qni_it on December 10, 2009

3 Comments so far

  1. WI Weather Buff December 11, 2009 7:27 PM

    Cool Beans! Eric, this is great stuff.

    You probably have some of the best educated (“meteorologically literate?”) viewers/readers/bloggers in the country!

  2. Renee December 11, 2009 7:46 PM

    So, Eric, is the NAO on a shorter time scale than the El Nino changes? Do you generally have both positive and negative NAO setups during any given winter season?

  3. Manolo Blahnik December 25, 2011 7:27 PM

    Inspiring article, Thanks. Keep posting.6wG8YwWP84bQ12-26


  1. White Christmas this year! December 15, 2009 5:49 PM
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  3. Setting our sights on a January thaw! January 8, 2010 5:35 PM
  4. Very cold end to January? January 21, 2011 4:00 PM

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