While you snow samplers in New Hampshire are gearing up for another icy blast from the north, I'm enjoying 60F here in sunny (and gusty!) Boulder, CO. The current deep freeze, like the preceding cold snap in early January 2014, is associated with the breakdown of the polar vortex. The jet stream took a big wobble in response to the disturbance of the polar vortex, bringing frigid cold air to the Northeastern US the first week in January.
Now it's happening again and you might be wondering... is this in any way related to the North Atlantic Oscillation (NAO)? The NAO was in a weak negative phase in early January and is hovering around neutral currently:
The polar vortex patterns we've been seeing this January are not necessarily being captured by the NAO, which is specific to the North Atlantic. If we expand to include the entire Arctic, we can see that the Arctic Oscillation (AO) has been in a negative phase (similar to a negative NAO phase). The negative AO phase is characterized by a very wobbly jet stream that bring cold, Arctic air southward.
Read more about how the polar vortex and Arctic Oscillation are related at ClimateWatch Magazine. Note the mention of the AO and NAO at the bottom of the article:
*While the AO describes the entire hemisphere, its close cousin—the North Atlantic Oscillation—is mostly confined to the North Atlantic Ocean. Because they are so closely related, they are often referred to interchangeably. The NAO is a fluctuating air-pressure pattern that alternatively enhances or blocks the storm-steering jet stream over the North Atlantic. The NAO and AO are measured using different indexes, but they are often referred to together as AO/NAO because their indices are typically strongly correlated during the winter. During the winter of 2009-2010, both the NAO and AO were in a very strong negative phase. This latest cold outbreak was one case where they were not in strong alignment; in early January 2014, the NAO index was near zero.
Date Posted: Jan. 21, 2014, 1:24 p.m.