More About the Polar Vortex

The meteorological term, polar vortex, is garnering quite a bit of attention lately in the United States. Some of us have not really been exposed to this term before. The reason why is simply because the polar vortex is just as the name implies, a polar thing. The winds associated with it flow in a broad cyclonic pattern around the polar regions (the southern hemisphere has its own winds that flow around the Antarctic region).

I've been reading many news articles about the subject. But, as reporters try to simplify why the cold air has invaded the region, there's just too many additional factors in play that cannot be explained fully in a short article. Frankly, for most of us, those explanations are over our head.

Right now, we have a weak polar vortex, which means if it was strong, it would resemble the map below.

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As mentioned before, though, we have a weak polar vortex as depicted in the map below.

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Although we often do not hear the 'polar vortex' term, perhaps we have heard of the Arctic Oscillation, similar to the NAO teleconnection, the North American Oscillation.

When the AO index is in the negative phase, the polar low pressure system (also known as the polar vortex) over the Arctic is weaker, which results in weaker upper level winds (the westerlies). The result of the weaker westerlies is that cold, Arctic air is able to push farther south into the U.S., while the storm track also remains farther south.

Therefore, a negative AO is directly proportional to a weaker polar vortex.

Here is a look at the current AO index from the Climate Prediction Center...

The AO index has been negative since late last month. It is expected to trend positive but will plunge again by the second half of the month. Therefore, expect additional weakening of the polar vortex in the coming weeks and along with that, the colder air for our region. Hopefully, the next wave of cold air won't be as brutal as our current one.

MS