How cold is it in the Upper Midwest today? It’s so cold that if you toss boiling hot water in the air, it may immediately evaporate. (Be careful out there and always check which way the wind is blowing, folks. People tend to scald themselves doing this.)
A polar vortex, as NOAA explains here, is a large area of low pressure and cold air surrounding the Earth’s poles. The “vortex” is the counter-clockwise flow of air that helps keep the colder air close to the poles. On occasion throughout winter, the vortex will expand, and send cold air southward with the jet stream.
The polar vortex is a large area of low pressure and cold air surrounding the Earth’s North and South poles. “Vortex” refers to the counterclockwise flow of air that helps keep the colder air close to the poles (left). During winter in the Northern Hemisphere, the polar vortex can shift, sending cold arctic air southward over the United States (right).
While we’re cooped up inside, we called Greg Carbin, who is in charge of NOAA’s Weather Prediction Center Forecast Operations Branch, to answer our questions about this blasted polar vortex sweeping the Northern parts of the U.S.
He shared one fact that blew our minds: The difference in temperatures across the contiguous U.S. on Wednesday is nearly 120 degrees. A temperature of minus 44 was measured in Bottineau, N.D., while temperatures in Imperial Valley, Calif., hit 74 degrees and rising.
How common is a polar vortex?
It happens every winter. Actually it’s not uncommon at all across the Northern Hemisphere in the winter.
Is it weird that the vortex is over the U.S.?
It shifts. This core of very cold air associated with the Arctic regions of the globe basically wobbles and shifts around. As you go through the winter months, the jet stream becomes unstable — and occasionally the system can wobble across parts of the North American continent where it’s not normally centered. That’s when we have what we call “Arctic air outbreaks.”
The farther north you are in the Northern Hemisphere winter, the more likely you are to experience this type of cold air. But it’s not uncommon at least once or twice a winter for that air to spread south out of the Arctic regions and into other parts of the Northern Hemisphere.
This is unusually cold, no doubt about it. We’ll establish some new records.
But events of similar magnitude have occurred in the past. The last one was back in 2004, and another one in the mid-’90s, and another one in the mid-’80s. Every few decades we see these events occur, where that arctic air that normally resides at the pole starts to make its way south into parts of the U.S.
Any reason why this is happening now?
It’s basically the most likely time for it to happen. You have snow and ice cover over a large part of the Northern Hemisphere. And so these cold air masses that have been generated over the past several weeks over the Northern climes can more easily translate south into the more Southern latitudes. This is the most likely time of the year that we would experience this type of outbreak: the middle of winter.
What happens next?
It’s not much consolation for those that are experiencing 50-below wind chills today across the Midwest, but [the freezing temperatures will be] relatively short-lived. We’ll see a change back to above-normal temperatures across much of the region by the beginning of next week.
Then another wobble in the jet stream will bring another mass of cold air south across the border with Canada and into parts of the Midwest and Great Lakes. That’s kind of an extended-range forecast, but it does look like we’re in a very changeable pattern right now, and so another outbreak is possible across some of these areas. Hopefully not quite as severe, but it’ll bring below-zero temperatures to Northern states in about two weeks.
And that cold air outbreak is also connected to the polar vortex?
It is. Again all of this cold air is kind of circulating around the Northern latitudes of the globe, and occasionally a chunk of it will break off and spread south. It’s very much the same dynamic that we’re experiencing now.
Is there anything new about this? The term “polar vortex” seems to have started being used more often, at least by NPR, around 2014.
It’s just a meteorological term that’s used to describe this cold air and the circulation that occurs during the winter months over the Northern latitudes.
I’m not sure why the phrase has all of a sudden caught on — it’s got that kind of techy sound to it. But essentially it’s been a phenomenon that’s pretty well understood for many decades. It’s been a meteorological term in use for quite some time.
Is this polar vortex connected to climate change?
Hard to say. The cold air is is unusual, but again it’s not unprecedented. I think we’ve seen similar events of similar magnitude that happen maybe once every decade or so. That’s part of climate.
The rapid swing from very cold to very warm is a bit unusual. We’re going to see 60-degree changes in temperature across the Chicago area in about four days. But linking that directly to climate change is a very difficult task, and usually we wait until after these events occur to try to come up with attributions for these events.
Right now it’s a little too early to say exactly why. But the likelihood of this happening in the middle of winter? The odds are in favor of very cold air outbreaks in late January.
Anything else we should know about what’s happening out there?
What I’m most impressed by today are the incredibly low daytime temperatures across the Midwest. They’re 19 below now at O’Hare [airport]. That’s incredibly cold for the middle of the day. What’s really going to be interesting is to see what kind of daytime records we set with this cold air mass.
Normally you associate really cold temperatures with the early morning, because temperatures drop overnight without the sun. Then once the sun comes up, even in the winter you can get some warmth out of that.
We’re not getting any warmth out of that today across the Midwest.
On the weather reports, we often hear very dramatic wind chill temperatures. Is wind chill a scientific thing?
It’s real. It’s good science: it’s based on the exposure of human flesh to apparent temperature. Since there’s moisture in our skin, it can evaporate and can actually cool a surface colder than the actual air temperature, and that evaporation is facilitated by the wind.
The ambient air temperature right now in some of these areas is 20 below. If there wasn’t any wind blowing, it would take a while for frostbite to set in — a few minutes. But with the wind, it can set in in a very short period of time because any moisture in your skin, any warmth, is just immediately removed by the wind.
As far as impacting other nonhuman things like structures? It doesn’t really have an impact. It’s based on evaporating moisture from skin.
The weather service issued wind chill warnings and wind chill advisories across a lot of the Upper Midwest today. They warn that exposed skin can freeze in as little as five minutes, if the wind chill is 40 to 45 below.
