Return of the polar vortex

By Doug Schneider

Over the next few days, you're probably going to hear the term "polar vortex" quite a bit, especially if you live in the northeast sections of the United States. I've seen a few scary-sounding headlines (much like we see with El Nino) that make it sound like Polar Vortex will come rolling into town and wipe out everything in its path.

The term "polar vortex" is nothing new to meteorologists, although it became popularized by the media during a major outbreak of cold temperatures in January 2014. The polar vortex is a large area of low pressure and cold air surrounding both of the Earth’s poles. It always exists near the poles, but weakens in summer and strengthens in winter. The term "vortex" refers to the counter-clockwise flow of air around the Poles. The polar vortex is located not at the surface, but at tens of thousands of feet up in the atmosphere. However, when we feel extremely cold air from the Arctic regions at Earth’s surface, it is sometimes associated with the polar vortex.

Normally, the polar vortex stays well north of the United States, keeping the intensely cold air in Canada, where it belongs. But sometimes a portion of the polar vortex will break off from the main circulation around the North Pole, and dip southward. The jet stream acts like a boundary that limits the southern extent of the polar vortex. 

This is a model depcition of what this week's polar vortex might look like (graphic from the Washington Post):

In that animation, you are looking at what's happening in the upper levels of the atmosphere, not at the surface. There is a large high pressure ridge over the Pacific and Alaska, producing warm temperatures aloft (the red-to-orange colors), and a deep low pressure trough over the eastern United States, with the green-to-gray colors showing the very cold temperaturea of the polar vortex lobe dropping southward into New England.

​This pattern of a large ridge over the Pacific and a southward dip in the jet stream across the eastern half of the United States is also typical of La Niña phase of the El Niño-Southern Oscillation. La Niña is when the water temperatures in the east equatorial Pacific Ocean are colder than normal. This affects the typical location of the jet stream across the northern Pacific and North America. A wintertime La Niña pattern in North America looks like this (graphic from NOAA):

The more southern position of the jet stream can allow a polar vortex lobe to drop farther south htan usual. Cycles of El Niño and La Niña occur every few years, varying in intensity and impacts on the United States. It is interesting to note that we are currently coming out of a very strong El Niño and into a La Niña, which is very similar to what occurred in 1982-83. December 1983 was brutally cold across much of the Lower 48, particularly New England.

So the polar vortex isn't something that's unprecedented or caused by "climate change" or global warming. Many major cold outbreaks in the past have been associated with a southward dip of the polar vortex, such as 1977, 1982, 1985, 1989, and 2014. There is no cause to be alarmed when you hear about the polar vortex, but you should be prepared for colder temperatures. Bundle up and stay warm.