In recent years, I've heard weather reporters describe "cut-off" low pressure systems which park over Southern Ontario for days at a time. In summer months, they bring us long stretches of cool cloudy, often rainy days. In only the last couple of years, there was mention of the "polar vortex" which seemed to unusually extend and deepen our winter last year.

I don't recall mention of either term in weather reports for the Southern Ontario region more than a few years ago.

Over the meteorological record for this region, are these new patterns? If they are not new patterns, is it simply a trend in weather reporting to apply these terms?

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    $\begingroup$ I'd say the latter. Polar vortices appear quite often on the south pole, and around the north pole it's simply less frequent. It's also known since the 90's that this phenomenon is linked to the strength of the Ozone hole, so I can't imagine that any meteorologist never heard about that. However I'm no expert on american weather patterns, so I just comment instead of answering. $\endgroup$ Commented Nov 22, 2014 at 16:15
  • $\begingroup$ With regard to the Polar Vortex, I understand that these circulations are well established phenomena. The question is about it apparently moving so far south and specifically in the region of the Great Lakes/Southern Ontario. $\endgroup$
    – Anthony X
    Commented Nov 22, 2014 at 16:19

1 Answer 1


The polar vortex

The AMS glossary defines the polar vortex as:

A planetary-scale mid- to high-latitude circumpolar cyclonic circulation, extending from the middle troposphere to the stratosphere. The Northern Hemisphere vortex often features two centers—one near Baffin Island and the other over northeast Siberia—with analogous circumpolar asymmetry atypical in the Southern Hemisphere. The westerly airflow is largely a manifestation of the thermal wind above the polar frontal zone of middle and subpolar latitudes. The vortex is strongest during the winter in the upper troposphere and stratosphere when the pole-to-equator temperature gradient is strongest. The stratosphere component of the circulation may be referred to separately as the “polar stratospheric vortex.” In summer, the strongest westerly circulation is largely confined to the troposphere, and the polar stratospheric vortex reverses in the upper stratosphere because of solar heating during the polar day.

This first descriptions of the polar vortex date back to the 1940s. You'll also note that the description above describes an upper tropospheric and stratospheric circulation e.g. this is is something happening well above the surface of the earth.

The recent popular use of polar vortex to describe any particularly cold air mass can probably be traced back to someone (either a meteorologist of psuedo-meteorologist) on twitter making reference to it and then "going viral". However the media got a hold of the word, they are quite consistent in misusing it.

The definition above mentions

The westerly airflow is largely a manifestation of the thermal wind above the polar frontal zone of middle and subpolar latitudes

What this means is that the position and strength of polar vortex (the circulation up around the stratosphere) is strongly influenced by the position of strong surface cold fronts coming out of the poles. The strong cold snaps are not the polar vortex, and the southern push of the high altitude polar vortex is a response of the cold snap, not the other way around.

Cut off lows

Cut off lows are not new either. A mid-latitude trough can be cut off from the westerly flow and you end up with a cutoff or closed low. These tend to be persistent, stationary mid and upper level lows that can last for days. You can see an example of a cut off low in the flow over the US in this video. Focus over the southern tip of Lake Michigan and you'll see it. These type of cutoff lows can occur anywhere in the mid-latitudes.

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    $\begingroup$ Agreed, the phenomena are in no way new, the terminology has just become the popular phrase of the day. Some mistake it a new phenomena in relation to climate change or to try to emphasize the severity of the conditions, but it is really just the currently popular terms and descriptors of specific weather conditions. These terms refer to weather, not climate or climate change. $\endgroup$
    – dlb
    Commented Jul 27, 2016 at 19:34

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