A rare “Polar Express” Winter pattern is forecast over the United States and Canada, following a Polar Vortex split
The recent Stratospheric Warming event is starting to impact global weather development. We already see colder air entering North America, but now a Polar Vortex split is forecast at lower levels of the stratosphere. This will bring a “Polar Express” weather pattern across the United States and Canada deep into the month, with multiple waves of cold air.
A “Polar Express” pattern is essentially a sequence of consecutive cold air events, with possible brief breaks. This usually requires a Polar Vortex core to provide a steady northerly flow over North America.
First, we will quickly look at what the Polar Vortex is and how it currently affects our weather. Then, we will focus on the upcoming Polar Vortex split and the potential winter weather outcomes for the rest of the month, the holidays, and even into 2026.
THE WINTER POLAR VORTEX
We often hear the word Polar Vortex, when we get close to winter. In most of our articles, we usually add some basic info for new readers. But to keep it simple, the Polar Vortex is just a name that describes the broad winter circulation over the northern (and southern) hemispheres.
Below, you can see a 3-dimensional image of the Polar Vortex. The vertical axis is enhanced for better visual presentation. This image shows the actual structure of the Polar Vortex across the atmosphere, connecting to the lower levels and the weather patterns below.
The Polar Vortex extends high up into the atmosphere. The lowest level of the atmosphere is called the troposphere, where all the weather events occur. But above that, we have the stratosphere, which is a deeper and drier layer.
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. Both parts together shape the winter circulation across the Northern Hemisphere and the resulting weather patterns.
To put the Polar Vortex into perspective, we produced a high-resolution video below that shows it in 3D, giving you a better idea of what it actually looks like.
The main takeaway from the video should be that the Polar Vortex is not just one winter storm or a cold outbreak that moves from Canada into the Midwest and over the eastern United States. It is the entire weather circulation over the Northern Hemisphere.
You can see the recent sudden stratospheric warming (SSW) event in the video, which is a rapid rise of pressure and temperature in the stratosphere. It is currently still impacting the Polar Vortex and, with some delay, also our daily weather.
STRATOSPHERIC WARMING AND DISRUPTION
Below is the analysis map for mid-stratosphere (30km/18.5miles height), and it shows a deformed Polar Vortex and a warming wave around it. It should usually have a nice circular shape, but you can see how a high-pressure area is pressing and changing its structure, and pushing it out of the pole. Image by weatheriscool
This is now already the aftermath of the stratospheric warming event, which peaked about a week ago. These stratospheric events are not like an on/off switch, but take time to start and can have lasting effects, even if the stratosphere starts returning to normal.
We can see this on the 3D Polar Vortex analysis below. While the upper structure is still deformed, it’s starting to regain some of its shape. But at lower levels of the stratosphere, you can see strong deformation and a connection to North America.
With a Polar Vortex core connected to North America, it has a strong impact on the pressure patterns and the daily weather across a large part of the region.
We can see this by looking at the pressure anomaly over the next few days. What stands out is the strong low-pressure anomaly over Canada and the United States, which is the lower part of the Polar Vortex core. That has a broad impact on air movement, creating a northerly flow into the United States and a southerly, mild flow into Europe.
The temperature anomaly forecast for the next few days shows this exact result, with a strong corridor of cold air spanning from the Polar circle across Canada and into the United States. This is the textbook example of a Polar Express pattern, with a direct flow of cold air into the United States and southern Canada.
Such a cold air pattern is usually hard to sustain, as the pressure systems move out, replaced by a new pattern. But thanks to the Polar Vortex and other global factors, we do see strong evidence of such a pattern lasting longer than usual.
To understand the full picture, we can look at the atmospheric pressure anomalies to have an idea of how these events “move” and impact the weather. Below, you can see the stratospheric warming anomaly marked in the red area. But in the forecast section, it’s clear how pressure anomalies from that event move lower over time.
This tells us that the stratospheric disruption was strong, and we are also seeing the signs of these events impacting the weather below in different ways.
Below is the latest analysis and forecast of the stratospheric winds around the Polar Vortex, which indicate its strength. The current values are low and well below normal (black line). But notice the second weakening around mid-month, which indicates another Polar Vortex disruption, and a possibility to extend the cold weather.
This always grabs our attention and needs to be looked into, as it usually indicates a possible winter weather impact in some shape or form.
POLAR VORTEX SPLIT
If we look at the polar vortex pressure forecast around mid-month, the new disruption is very obvious. This map shows the lower stratosphere at the 50mb level (20km/12.4miles), with the inner core of the Polar Vortex split into two areas. This is caused by the strong high-pressure systems from below, pushing into the Polar Vortex, just like squeezing a balloon.
This is an important event for this time of year. Any large-scale pressure changes in the stratosphere at this time can mean substantial weather impacts.
A Polar Vortex split occurs when the high-pressure waves break the main stratospheric low-pressure core into two (or more) parts. These breakaway cores then tend to bring colder air and snow to wherever they move, while enabling a warmer pattern further downstream.
Below is the pressure/temperature forecast for the same level. In this image, you can better see the two low-pressure inner cores of a split Polar Vortex, also called “daughter vortices”. This is a bit further into the forecast, around mid-month, and shows a stronger core to settle over North America.
Such a core split of the Polar Vortex usually means a high-pressure area will build over the polar circle at the surface. As the Polar Vortex is split, the remaining cores and the cold air move towards the mid-latitudes. In this case, we see one core move over Asia and one over Canada and the United States.
The atmospheric forecast image below shows the pressure anomaly by altitude from the surface to the top of the stratosphere. You can clearly see how the Polar Vortex is split in half, with one core connecting down into the United States and Canada. At the same time, a high-pressure anomaly builds over Europe with mild weather.
Below is also a 3D structure forecast of the Polar Vortex for around mid-December. You can nicely see the split structure, with one core moving towards North America. This means regional impacts for the United States and Canada, as the Polar Vortex core usually brings along a larger supply of cold air.
This is mainly achieved because the Polar Vortex core is a strong low-pressure area, spinning counterclockwise. That enables a northerly flow across North America, with cold air and snowfall where moisture is available.
The surface temperature forecast for the Polar Vortex split period shows a large pooling of cold air over Canada. This is due to the Polar Vortex in the area, creating a stable northerly flow, pushing the cold deeper into the United States. But on the other side of the Atlantic, its impact brings a westerly-to-southerly flow and mild conditions.
With all the forecasts in mind, the main area of coldest air looks to be over North America, where one of the split Polar Vortex cores will directly move over and impact regional weather patterns.
On the other hand, it looks like Europe will be under a prolonged mild pattern, with no real cold air supply and limited snowfall over higher altitudes.
We will look more closely at the weather patterns in this period and beyond, and how the Polar Express pattern will establish over the United States and Canada.
POLAR EXPRESS WEATHER ANOMALY
A Polar Express pattern is a sequence of repeated cold waves moving from the Polar Circle into Canada and onwards into the United States. It usually forms when a Polar Vortex core settles over North America, creating a steady northerly flow that can channel colder-than-normal air into the United States and southern Canada.
The 15-day stratospheric forecast at the 50 mb level (20km/12.4 miles) shows continued core separation. But you can see that the stronger core remains over the North American sector, indicating continued support for a cold pattern into the United States and Canada.
The pressure forecast for this period shows the continued presence of the low-pressure zone over the United States and Canada. This supports a stable northerly cold flow, also known as the Polar Express, which usually means multiple cold waves into the United States. But further east, this creates a warmer flow across the Atlantic.
This warmer flow is forecast to enter Europe, helping to create a high-pressure pattern with warmer-than-normal temperatures. It can also limit precipitation and locking snowfall into higher elevations. This is expected to last well into the second half of the month.
The ensemble temperature forecast for the same period shows a strong cold airmass spreading across the northern and eastern United States and southern Canada. This is exactly what we expect to see in the days following a Polar Vortex split event. But this is an average of multiple calculations, so it looks “weaker” at this range, and gets stronger once all the calculations agree on the final scenario.
Looking at a single-forecast example for this same period, we can get a better idea of the potential outcome. You can see a strong cold air outbreak starting over Canada and quickly making its way into the northern and central United States, and then also spreading east.
This is probably the best practical example of a polar express pattern, where cold waves follow one after another. Brief mild breaks are also possible as the flow resets. But as long as the Polar Vortex remains over Hudson Bay, this pattern will persist.
The question now is how long we expect this pattern to persist. For that, we can find an answer in the extended range forecasts.
HOW LONG WILL THE COLD LAST?
Based on the expected Polar Vortex split progress and extended forecasts, the colder pattern over the United States and Canada is expected to persist well into the second half of the month and can influence the weather around the holidays.
As long as the Polar Vortex core and the low-pressure zone remain in place over North America, repeated cold air events are likely in the United States. As a result, Europe is more likely to stay under a milder, high-pressure pattern. This is evident in the ECMWF forecast below for the last week of December, which shows a similar pattern continuing around the holidays.
The temperature forecast for the holiday week shows a continued cold mass over Canada and an extension into the northern and eastern United States. This is an extended-range ensemble forecast, which usually shows a weaker event due to range. But this already looks like a strong anomaly and gives confidence in a snowy Christmas across the northern and eastern United States, and partially across the Plains.
Looking further ahead into early January, we can still see the Polar Vortex core area over Canada. This indicates that the cold pattern could continue into the new year. But since this low-pressure system looks more compact, it opens the door for an easterly flow to finally develop over Europe.
The latest CanSIPS long-range forecast was just released, and it shows the easterly cold air to start entering Europe in its January 2026 forecast. This is due to the higher pressure area over the north, spinning clockwise. In reality, such a pattern would bring the cold air further up into the UK and the north-central parts.
The same forecast for North America shows the expected sustained cold Polar Express pattern to continue into January. You can see the cold air source region over western Canada, and the cold channel into the northern and central United States, the Midwest, and the northeast.
So far, the forecast consensus shows that the colder air anomaly over North America is expected to last into December and continue into January 2026. Brief mild periods can occur between individual cold waves.
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, using a commercial forecaster license.
Don’t miss:
Seasonal Snowfall Predictions show a strong start of the 2025/2026 season across North America
