We're well used to hearing about polar vortexes (vortices?) these days. But what I hadn't realized is that we've always had polar vortexes, and they usually just sit there being polar vortexes without any need to report them, with great drama and stürm und drang, on the evening news.
What causes us to take note of them, and to be affected by them directly, is when there is a "polar vortex collapse" event.
The polar vortex is really just the normal winter circulation of air over the Arctic (and Antarctic). It extends from the lower troposhere part of the atmosphere (which is where what we experience as weather occurs) and the upper statosphere, and the two layers interact to some extent. A stable or strong polar vortex is usually constrained by the jet stream, so that the ferocious extreme cold of the high Arctic does not leak into the regular winter cold of northern North America.
However, when there is a weak or disrupted polar vortex, the resulting weakened jet stream cannot contain the polar vortex, and cold air escapes or leaks in a few places into the more-inhabited south, creating intensly cold and snowy conditions, like we are expecting later this month. This is known as a polar vortex collapse, although it is just a temporary collapse, usually from a few days to a few weeks.
You can get much more detail on this from the Severe Weather Europe website, but that, in a nutshell, is most of what you need to know to impress people at your next dinner party, when politics and religion starts to become too awkward.
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