Polar Vortex Watch: A Stratospheric Warming event is about to start, with Cold Weather and Snow to follow behind
A significant disruption of the Polar Vortex is about to start, due to an unusually early Sudden Stratospheric Warming Event. The forecasts show a collapse of the polar circulation in the second half of the month, with cold weather and snow to follow across the United States and Canada, but with less clear impacts over Europe for now.
The Polar Vortex is usually the “keeper” of cold, locking it into the polar regions when strong. But when disrupted or collapsed, the cold air can escape, creating proper winter weather across the mid-latitudes.
In this article, we will look at the structure of the Polar Vortex and its current state. Then you will see how the upcoming stratospheric warming will help to bring cold and snow across the United States, Canada, and potentially also Europe, creating a “December to remember” and potentially even a white Christmas.
THE POLAR VORTEX SIMPLIFIED
To understand what the Polar Vortex is and how it works in a simple way, you don’t need to be an expert. In simple terms, the Polar Vortex is a name that describes the broad winter circulation over the northern (and southern) hemispheres.
You can simply imagine the Polar Vortex as a “wall” spinning over and around the polar regions from the surface to the stratosphere (over 50km/30miles high), containing the cold polar air inside.
For this reason, we separate the entire Polar Vortex into an upper (stratospheric) and a lower (tropospheric) part. They both play their role differently, so we monitor them separately. But both parts together form the whole winter circulation and the resulting daily weather at the surface.
We closely monitor the strength, shape, and size of the Polar Vortex, and separate it into two main “modes”:
When the Polar Vortex is strong, it means a strong polar circulation. This locks the colder air into the polar regions, preventing its escape, and creating milder conditions for most of the United States, Europe, and other mid-latitudes.
But when the Polar Vortex gets disrupted or even fully collapses, it has a much harder time containing the cold air, which can now easily escape from the polar regions into the United States or other mid-latitude regions. Below is an example of how a disrupted Polar Vortex helps to release the cold polar air into the United States and Europe. Both images are by NOAA-Climate.
If you prefer a warmer/milder Winter across the United States or Europe, you will like a strong Polar Vortex. But if you want proper Winter weather with cold and snow, a weak/disrupted Polar Vortex is exactly what you want to see.
For the best presentation of what the Polar Vortex is, we produced a high-resolution video below. It shows the Polar Vortex in true 3D, giving you the best possible idea of what it actually looks like if you were ever able to see it. Video shows the latest Polar Vortex forecast and the start of its disruption.
The main takeaway from the video should be that the Polar Vortex is one large circulation, connected through the atmosphere.
We will now look at the latest analysis and the upcoming Stratospheric Warming event, and how it will help to unleash colder weather and snowfall in the days and weeks after the event.
POLAR VORTEX AT PEAK STRENGTH
The latest analysis shows that the Polar Vortex currently has a normal size, a nice circular shape, and is running around the long-term average strength. You can see geopotential height and temperature analysis in the mid-stratosphere at the 10mb level (30km/18.5miles height). The stratospheric Polar Vortex looks like a large “cyclone” with a cold core near its low-pressure center. Image by weatheriscool.com
While the Polar Vortex looks decent at this level in the stratosphere, you can already see the first signs of trouble. A high-pressure area is starting to form, with a weak warming wave already visible in the outer layers.
In the image below, you can see the pressure anomaly at the same level in the stratosphere, which shows that the main core of the Polar Vortex is running with properly low pressure. But here you can better see the developing high-pressure anomaly in the stratosphere, which his expected to grow and strengthen further.
If we look at the 3D analysis of the Polar Vortex below, you can see its full structure. It has a good circular shape, and you can also see how it connects to the lower levels, extending its “cold arms”, which are actually areas of low pressure. You can see an arm, which has brought the current cold polar air into the eastern United States.
We often talk about the “strength” of the Polar Vortex. But how do we actually measure it? The simple answer is the winds. The more organized the stratospheric Polar Vortex is, the stronger the winds around its core, which usually translates to a stronger influence on the surface.
Below is the latest analysis and forecast of the stratospheric winds around the Polar Vortex. The black line shows the long-term average, and the other lines are different forecasts. You can see that all forecasts indicate a power reduction of the Polar Vortex over the next two weeks, as the high-pressure area expands in the stratosphere.
An important threshold is the 0 line, which marks an actual wind reversal in the stratosphere. One of the latest GFS forecasts now shows a reversal, which would mark this event as a major Sudden Stratospheric Warming (SSW). But surface weather impacts can also occur without an official wind reversal, if the Polar Vortex is disrupted enough.
Below is a simple schematic of how a Polar Vortex starts to weaken during a startospheric warming event. The main disruptive energy comes from the lower levels first, with atmospheric waves reflecting energy up into the stratosphere.
This energy starts to disrupt the Polar Vortex by creating areas of higher temperature and pressure in the stratosphere. The disruption of the Polar Vortex then allows cold air to more freely escape the polar regions, covering the United States and/or Europe in Winter in the process.
Most SSW events occur in mid-to-late winter. But this year, the forecast shows an unusually early stratospheric warming event, just in time to impact the start of the meteorological winter.
STRATOSPHERIC WARMING EVENT 2025/2026
The latest forecasts show the peak disruption to occur later this month, around the 26th. In the image below, you can see a very strong high-pressure area in the mid-stratosphere, sometimes called the “anti-vortex”. You can see a very strong warming wave occurring where they come together, deforming and disrupting the Polar Vortex.
Below is the mid-stratosphere pressure anomaly forecast for the same period. In this image, you can clearly see the large high-pressure anomaly in the mid-stratosphere at the 10mb level (30km/18.5miles height), squeezing the Polar Vortex, slowing it down, and creating a big disruption in the atmosphere.
The true extent of the stratospheric warming event can be seen in the latest temperature anomaly forecast for the same level. You can see a strong warming anomaly, with the temperatures in the mid-stratosphere nearing 40 degrees C above normal.
Such a stratospheric warming event is quite unusual at this time of year. There are fewer than a handful of these stratospheric events recorded this early in the past 70 years, with this being the earliest on record, if it manages a proper wind reversal.
Below is also a 3D forecast of the Polar Vortex for later this month. You can clearly see a highly disrupted structure and a deformed core, with a warming event at the top. This shows a major impact on the Polar Vortex, from which surface impacts can be expected in the following 5-10 days.
At this point, we can start to ask the question: how will this event impact the weather at the surface? To answer that, we first need to find signs of it actually making progress downwards from the stratosphere.
In the forecast graphic below, you can see the pressure anomaly forecast for the lower stratosphere on the 26th. It shows a strong high-pressure anomaly and a clearly displaced Polar Vortex. This is a clear sign of this event having a rapid response in the atmosphere.
But if we go even lower down, to the bottom of the stratosphere at the 100mb level (16km/10miles height), we can look at the zonal wind speeds again. The forecast clearly shows a reduction in the wind speeds, which indicates the arrival of the stratospheric warming effect at lower altitudes.
These warming events are notorious for having weather impacts all the way to the surface levels. And we can look at past events to give us an idea of what to expect.
STRATOSPHERIC WEATHER CHANGES
Below you can see the surface pressure pattern 0-30 days after a stratospheric warming event. This is a combined image of several past events, so it gives us an idea of what we can usually expect after at the surface. You can see the high-pressure area over the pole, displacing the low-pressure areas around.
That means a weakened jet stream and low-pressure systems from the eastern United States across the North Atlantic and into Europe. This helps to unlock the cold air from the Arctic, sending it towards the United States, Canada, and Europe, as shown in the image below.
The images above show an average picture of many SSW events. But each stratospheric warming event is different and does not automatically mean a strong winter pattern is coming.
But we have checked past data and found only 3 stratospheric warming events that occurred this early in the season in the past 70 years. The seasons were 1958, 1968, and 2000, with stratospheric warmings in November. Two of which had a full wind reversal, and with 2000 just a weakening.
Below you can see the surface temperature anomaly in the following month of December from PSL. It is very clear that these early events featured a cold weather pattern over Canada and the entire United States, except for the southwest.
For some reason, Europe shows a rather weak response, with just some cooling evident over the northern and north-central parts. The main polar cold release occurred in the central and whole of eastern United States.
For the 2025/2026 season, we will look at the extended range forecasts, which will show us if we can expect the same cold weather response following the upcoming early SSW event.
COLD WEATHER AND SNOW FOLLOWS
A we have seen, a stratospheric warming event usually means that high-pressure anomalies from the stratosphere can make their way to the surface. This disrupts the jet stream, helping to release cold air from the polar regions down into the United States, southern Canada, and Europe.
Below is the surface pressure anomaly forecast for the first half of December, and it shows the exact same pattern as expected following an SSW event, seen above. A high-pressure area over the pole, with low-pressure systems displaced along with the cold air into the United States and the eastern hemisphere.
As the main impact region seems to be North America for now, we can look closer at the 500mb (5km/3miles) pressure anomaly forecast for the first half of December. You can see how the forecast shows the expected blocked North Pole, with a broad low-pressure area creating a northerly cold flow into the United States from western Canada.
This is exactly what we would expect to see following a strong disruption of the Polar Vortex, just like the past events have indicated. We can see this as a strong sign of a cold and snowy start to Winter across the United States and southern Canada.
The temperature forecast for the first half of December indicates a potentially strong release of cold polar air into the northern, central, and eastern United States. This is a growing trend in recent days, showing colder anomalies and a proper winter pattern, as expected following an SSW event.
Over Europe, we currently see support for a cold air anomaly mainly over the northern parts, and potentially into the UK, if the low-pressure area sits lower. But, this is again exactly the same scenario as we have seen in past early SSW events, which tend to strongly favor the United States and Canada with cold air and snow.
We are still early in the process, and these stratospheric events are not all the same. So, there is still more than enough time for the forecasts to show colder air spreading into the central and northwestern parts, as some mid-winter SSW events tend to do.
Looking deeper into December, we can see the cold air anomaly continues to spread, now reaching further up into northwestern Canada. This tells us that the forecast expects the northerly flow to remain stable, pulling colder air from the deep polar region, transporting it down into the United States.
Such a pattern could stay stable into late December, greatly increasing the chance of a white Christmas across many parts of the United States.
Looking at the snowfall forecast for December, you can see a good spread of total snowfall from Canada into the northern, western, and eastern United States. The snow cover also spreads over the Plains. This is an ensemble average, so we are only looking at coverage, not the actual numbers.
This is another positive sign for a good chance of a white Christmas deeper to the south of the U.S. than in some recent winters.
Based on the snowfall trend above and the surface temperature pattern below, this trend looks really promising for now, as we can see snow cover and colder temperatures over a large part of the United States. Such a forecast combination is exactly what you would want to see early on.
Of course, we have to keep in mind that this is a far extended range. But what gives us good confidence is that this is not some random forecast, but a pattern following a stratospheric warming event, backed by other early events that had the exact same outcome in the past.
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The main forecast images in this article are from WeatherBell, using a commercial forecaster license.
Don’t miss the current ongoing cold air event across the northern, central, and eastern United States:
Early cold weather across the United States, November 2025
