— -- The polar vortex is not moving over the United States this week, regardless of what you may have heard or read, but that doesn't mean that winter weather is not only starting early, but already packing a punch.
The polar vortex is real, and the meteorological community has known about it and used the term for decades. It is an almost always present upper-level circulation that hangs out over the poles. It is not at the surface and is not related to every push of cold air.
Remember the first time you heard the term last winter?
Here's what was happening:
The polar jet stream is like a fence keeping the air influenced by the polar vortex in place.
During the first week of January 2014, the polar jet stream was kinked enough to build a large ridge in the west and allow a lobe of the polar vortex to slip into Canada, greatly influencing the air that set records in the northern plains and Great Lakes.
This has happened before, and for longer periods of time, such as in the late 1970s, but the term polar vortex did not get picked up back then by the general population.
Since January 2014, the term polar vortex has been used -- and abused.
If we called every push of cold air the polar vortex it would lose its meaning and not be accurate. If the actual polar vortex was moving over the United States, we would have much bigger planetary problems to cope with.
So, what is really going on this week?
There is a large ridge in the jet stream, in part enhanced by the remnants of the Pacific Ocean storm Nuri, out west and a huge trough east of the Rockies. This trough is allowing air that is influenced by the polar vortex, which is still above the poles, to flow down toward Canada and the northern United States.
As a result, the northern Plains and Great Lakes will be colder than average. Many areas will see their first snow of the season. But this is not the polar vortex itself. It is air influenced by part of the polar vortex.
Looking ahead, the pattern that is setting up will likely stick around for not only this week, but the majority of the final weeks of November.