The Polar Vortex is known as the “keeper” of cold, locking it into the polar regions when it is strong. But a disruption of this system can unleash the Arctic floodgates, sending a release of freezing air into North America and Europe.
Using the latest forecast data, we will look at the progress of the Polar Vortex disruption and the large-scale release of cold polar air, which is expected to bring a prolonged period of winter weather over the Northern Hemisphere.
Polar Vortex: Steering the Cold Flow
Since we have a lot of new readers, or readers not that familiar with the Polar Vortex, we include a very short rundown on what the Polar Vortex is and why it matters each Winter.
In simple terms, the Polar Vortex is a name for the broad winter circulation over the northern (and southern) hemispheres. You can imagine the Polar Vortex as a spinning wall over the polar regions, rising from the surface into the stratosphere (over 50km/30 30miles high) and trapping the cold polar air inside.
As you can see in the image below, the Polar Vortex is separated into two layers that we monitor at all times around wintertime: the stratosphere and the troposphere. The first one is a higher layer, and the second is at a lower altitude. The Polar Vortex rises through both layers, but with different shape, strength and impacts.
For this reason, we separate the entire Polar Vortex into an upper (stratospheric) and a lower (tropospheric) part. A strong Polar Vortex can lock the colder air into the polar regions, preventing its escape. This usually creates milder conditions for most of the United States, Europe, and other mid-latitudes.
But when the Polar Vortex gets disrupted or collapses, it can no longer contain cold air, opening the Arctic floodgates. This allows the cold air to escape from the polar regions into the United States and other mid-latitude regions. Below is an example of how a disrupted Polar Vortex brings cold polar air into the United States and Europe.
This weak/disrupted Polar Vortex is exactly what you want to see if you like cold weather across the United States, Canada, and Europe. The disruption itself usually comes from the rise in pressure and temperature in the stratosphere, called a Stratospheric Warming (SSW) event.
To better understand what the Polar Vortex is, we produced a high-resolution video below. It shows the latest Polar Vortex forecast in 3D, revealing the upcoming disruption event. This will deform its structure and allow cold air to escape as the Polar Vortex core moves out of the polar regions.
Now, we will look at the latest state of the Polar Vortex and how its disruption will bring down the coldest air of the season so far across the United States and Canada, and a cold wave into Europe.
The First Disruption: A Chain of Events Begins
The latest analysis shows that the Polar Vortex is currently in an elongated shape, also known as a “stretched” vortex. Below you can see geopotential height and temperature analysis in the mid-stratosphere at the 10mb level (30km/18.5miles height). Such elongation can help to produce a northerly flow into North America. Image by weatheriscool.com
Especially in cases with a strong North Pacific high-pressure area, it can really bend the jet stream down into the United States, allowing a cold air outbreak.
In the forecast graphic below, you can see the pressure anomaly forecast for the lower stratosphere at the 50mb level (20km/12.4 miles). It shows a strong high-pressure anomaly over northern Canada and a displaced Polar Vortex core. This supports the northerly flow at the surface levels over the eastern U.S., with the core reaching into eastern Canada.
This is nicely seen in the temperature forecast below for the next few days. You can see a strong cold-air corridor into southern Canada, extending into the northern, central, and eastern United States, reaching down into the southeast and Florida. This is the direct reflection of the Polar Vortex core moving aloft.
Looking over Europe in this period, you can see colder air returning at the surface levels, under a high-pressure anomaly. This means very likely inversion and cold air pooling at the surface levels, with the cold airmass coming from the east.
But as you will see, this is just the start of the Polar Vortex disruption, with another cold air wave to arrive as the Polar Vortex becomes more unstable.
A New Stratospheric Warming Signal
As mentioned, the Polar Vortex gets unstable with a rise in pressure and temperature in the stratosphere, putting stress on its structure. This is also known as a Stratospheric Warming Event (SSW). It can be a major one or a minor one, but it can always have an impact on the Polar Vortex and the weather below.
Below is the GFS pressure and temperature forecast for early next week, in the mid-stratosphere at the 10mb level (30km/18.5miles height). You can see a strong high-pressure area (H) in the mid-stratosphere, and a strong warming wave starting between the pressure zones.
This would count as a weaker stratospheric warming event, since the Polar Vortex is not collapsed, and the stratospheric winds are not reversed. But you can see the deformation of the Polar Vortex structure, a core split, and this is a prelude to the second phase of disruption coming a few days later.
Below is the lower stratosphere pressure anomaly forecast, also for early next week. In this image, you can clearly see the large high-pressure anomaly in the lower stratosphere at the 50mb level (20km/12.4 miles), disrupting the Polar Vortex, creating a stronger core split, and sending one core into North America, to impact the United States and Canada.
We also produced a 3D forecast of the Polar Vortex for this period. You can see the disruption and warming in the upper stratospheric levels. That translates into the whole structure, where you can also see how the Polar Vortex is “compressed” from the strong high-pressure systems in the lower levels. So its a combined effort of the atmosphere to disrupt the Polar Vortex.
The main result of this deformation, as you can nicely see in the 3D image above, is the arrival of the lower foot of the Polar Vortex into North America, connected to the core structure of the Polar Vortex.
Usually, when we see a Polar Vortex structure like that, it’s almost certain that a cold air release is coming. We can easily track where the cold air will land by finding where its core and “foot” are. This usually signals that the Arctic floodgates have opened.
Below is the temperature anomaly forecast from ECMWF for early next week. You can see a strong cold-air anomaly spanning from southern Canada into the whole central and eastern United States. The strongest cold anomaly is found over the Midwest, but anomalous cold air will reach far down to the south and the northeast.
The lowest U.S. temperatures in this period are expected across the Midwest and the Northeastern United States, going below 0-5°F, with parts reaching below 0°F. The far northeast and the upper Midwest can see minimum temperatures in this period reach between -5°F and -10°F. Near-freezing lows can reach the south coast and northern Florida.
Southeastern Canada may experience temperatures as low as -25°F to -30°F (-30°C to -35°C) during the cold next week.
Current forecasts also show good snowfall potential in the next 7 days. Below is the ECMWF total snowfall forecast, with snowfall detected over a large part of the Midwest, also with decent amounts around the Great Lakes, due to lake-effect snowfall.
Looking over Europe in this period, you can see colder air coverage increasing towards the west. The western and southwestern parts can reach near or below freezing, with lowlands in the central parts going below -5°C to -10°C, and even lower to the east.
This is a typical result of a very disrupted Polar Vortex circulation at the lower levels. But the latest forecasts show an even stronger disruption is coming, fully opening the Arctic gates in the last week of January.
Stratospheric Disruption and Breakdown
We will first look at the 3D forecast of the Polar Vortex for the final days of January. There is a very obvious stratospheric warming anomaly in the stratosphere, strongly disrupting the Polar Vortex. That deforms the whole structure, making the lower Polar Vortex push out its cold “feet” into the United States and also Europe.
We can see this strong shift if we look at the pressure anomaly in the lower stratosphere at the 50mb level (20km/12.4 miles). You can see a spectacular low-pressure anomaly as the main core of the Polar Vortex gets pushed into North America. This is a very strong event, with the lower core of the stratospheric vortex rarely reaching this far down.
The reason for such a strong disruption event is not only the warming in the stratosphere, but also the strong high-pressure systems in the lower levels of the atmosphere. Below is a special forecast that shows the wave reflection into the stratosphere. You can see a peak in the next two weeks, generating the outcome above. Image by Simon Lee
In simple terms, a stratospheric wave reflection is like a massive atmospheric ricochet. The energy from large pressure systems moves upward into the high atmosphere, but during a reflection event, it hits a “ceiling” in the Stratosphere and bounces back down to Earth.
This returning energy slams into the lower atmosphere, disrupting the Polar Vortex and the jet stream, opening the Arctic gates to freezing air, sending it into North America and/or Europe.
Below is the 500mb pressure anomaly forecast for late January, and it shows a perfect example of the cause/effect for a Polar Vortex disruption and a reflection event. Strong high pressure blocking over the polar regions acts like a “hammer”, dropping down on the cold air, pushing it out into the United States and Europe.
You can see an overall disrupted look, which is usually a clear sign of a complete breakdown of the polar circulation in the lower levels.
We can also see this below on the vertical pressure forecast for late January, from the surface to the top of the stratosphere. You can see the Polar Vortex broken into two “legs” connecting down into the United States and Europe. This shows the direct connection of Polar Vortex cores to the surface.
This shows the direct impact and influence that this Polar Vortex disruption is forecast to have. But what can we actually expect in terms of cold and snow?
The Arctic Floodgates Open
The airmass temperature anomaly for days 10-15 really nicely reveals the whole “Arctic floodgates” process. You can see the complete temperature reversal, where warmer-than-normal air reaches into the Polar circle, pushing the cold air out into the mid-latitudes as the polar circulation breaks down, and the Polar Vortex “walls” are unable to hold the cold air any longer.
The forecast above is for the airmass anomaly, which is at the 850mb level, around 1500m (5000ft). This allows us to track the large-scale movement of colder and warmer air.
Looking at the surface temperatures now, you can see a high-resolution forecast from ECMWF for around the 26th. It shows the temperature anomaly, revealing a strong cold air outbreak, with temperatures reaching 20°F to over 35°F below normal. It truly is as strong as it looks.
Keep in mind that an anomaly shows the above/below temperatures compared to the normal (long-term) values. So having a forecast 30°F below normal in late January is much stronger than in early December, as the normal values are lower.
Also note that this is a single-run example of the potential scenario. While this is around 10 days ahead, it’s starting to come into the more reliable range. But the main idea is in place, for a major cold air outburst from the Polar regions.
A cold outbreak of this magnitude is forecast to bring some of the coldest temperatures of the season so far across southeastern Canada and the United States. Below you can see examples of the lowest temperatures in southeastern Canada reaching down to -35°F and lower, peaking near -40°F too.
A large part of the Midwest shows negative temperatures, reaching down to -20°F in the upper Midwest, and below -25°F in parts of the Northeast. Freezing temperatures are forecast to cover much of the country, including northern Florida, with low 30s and low 40s as the highest in the country over the southwestern United States.
Looking at Europe, the temperature anomaly forecast for this period shows a supply of colder air over the northern parts. But because there is a low-pressure area in the North Atlantic, this is likely to create a (brief) mild period over the western and southern parts.
Looking at the total snowfall forecast for the next two weeks, you can see that a good amount of snowfall can come with the cold air. This is just a single run forecast, but serves as a great example of the true winter potential of this cold airmass. Over half of the United States will see snowfall at some point by the end of January.
Over Europe, the snowfall coverage is also great, with snowfall reaching down into the southern parts and deep towards the southeast. On the North American side of the forecast, you can also see the strong snowfall around the Great Lakes, due to lake-effect snow.
But going further ahead into early February, the ECMWF extended ensemble temperature forecast shows support for continued cold air over the eastern and northeastern United States and southeastern Canada. This is a 7-day average, but the trends for now support the colder temperatures in the east, while warmer temperatures return over the western half.
Over Europe, the temperature forecast for this period shows the colder air covering most of the continent, under a northeasterly flow and lower pressure. This is just a trend forecast for now, but it shows a continued cold air push from the northeast, lasting into February.
This article is based on the latest available model/ensemble data, and we will continue to release weekly updates on the developing Polar Vortex situation during the winter season.
We will keep you updated on the global weather pattern development, so don’t forget to bookmark our page. Also, if you have seen this article in the Google App (Discover) feed, click the like button (♥) there to see more of our forecasts and our latest articles on weather and nature in general.
The main forecast images in this article are from WeatherBell and weathermodels.com, using a commercial forecaster license.
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