A “cold train” weather pattern is coming for the United States in the second half of January, as a strong high-pressure zone rises over western Canada and Alaska. It will create a cross-polar flow that brings down colder air. This is aided by the strong Polar Vortex region in eastern Canada.
The Polar Vortex is undoubtedly one of the most important short-to-medium-term weather factors during the cold seasons. It is strongly connected to all levels of the atmosphere, from the ground. Any significant change, especially disruption, of the Polar Vortex could have a profound impact on weather development.
This is why we pay attention to activity high in the stratosphere and monitor the situation regularly. The Polar Vortex will play an important role in bringing cooler weather to the United States in the coming days and weeks.
We will first quickly and easily explain what the Polar Vortex is and why it is so powerful. This is an important part every winter season. We try to explain it in all our winter articles. This knowledge can really help us understand the larger picture of how the weather works worldwide.
THE POLAR VORTEX
The Polar Vortex can be described as a large cyclonic circulation that covers the entire north pole and the mid-latitudes. It is present at all levels, including the ground and the middle atmosphere. However, it can take different shapes at different elevations.
The Polar Vortex is so vast that it can be broken into two parts. One is the lower (tropospheric), while the other is the upper (stratospheric). The stratospheric polar vortex plays an important role in weather development, while the lower tropospheric polar vortex actually “is” the weather and drives it around.
But what exactly is the stratosphere, you ask? The troposphere is the lowest layer in the atmosphere. It is where all weather takes place. It can reach as high as 8 km (5 mi) in the polar regions and around 14-16km (9-10 miles) above the Equator.
The stratosphere is a layer that is much deeper than the one above it. This layer is about 30 km/18.5mi in depth and very dry. This is the location of the Ozone layer. The image below shows the layers of the atmosphere. You can see the troposphere and weather at the bottom, and the stratosphere above it.
The image below shows an example of the upper Polar Vortex located at 30km/18.5miles above the middle stratosphere in winter. It is a circular shape because it has very little that could disrupt its circulation under normal conditions.
The polar vortex is shown at a lower altitude (around 5km/3miles) in the next image. It shows the true size and shape of the polar vortex closer (cold colors). Because it interacts with terrain and the dynamics of various weather systems, the polar vortex will become more deformed as it gets closer to the ground.
Be aware of its cold arms or “lobes” extending into the lower latitudes, bringing colder air and snowfall into the mid-latitudes. These arms also pack a lot of energy and can create strong winter storms, like for example Nor’easters in the United States or very strong wind storms across the North Atlantic.
A strong Polar VortexThis is usually a strong polar circulation. This can often lock the cold air into the Polar regions, creating milder seasons for most of the United States.
On the contrary, a weak (wavy) Polar VortexIt’s just as dynamic as it sounds. It is much more difficult to contain the cold air. However, it can now be released from the polar regions into the United States and/or Europe. Image by NOAA.
You can get a better idea by watching the video below. It shows the Polar Vortex spinning above the Northern Hemisphere at 23km/14miles elevation.
The NASA GEOS-5 forecast for November is shown in this video. Notice how the polar Vortex covers a large portion of the Northern Hemisphere. It is easy to see how it spins across the Northern Hemisphere and connects with the weather circulation at the lower levels.
But how and where does the polar vortex form?
As we approach autumn, the sun starts to decrease in the polar regions. This means that the north pole is cooling. However, as the polar areas cool, the atmosphere further south remains relatively warm since it continues to receive energy form the Sun. On the image below, you can see that the winter solstice occurs when the polar regions receive very little or no solar energy compared to those further south.
As the temperature drops in the polar regions, the pressure also drops. As the temperature differential towards the south increases, a large, low-pressure (cyclonic), circulation begins to form across the Northern Hemisphere. It originates from the top layers and reaches the stratosphere. This is known as the Polar Vortex.
Although the stratospheric vortex is spinning above our weather, it is still directly linked to the lower levels. It can shape our daily weather in one of several ways as one large circulation that covers the entire hemisphere.
Below you will find that there is a strong Polar Vortex in our stratosphere, but one weaker in the lower levels. This will create a unique weather pattern in the Northern Hemisphere.
POLAR VORTEX and THE WEATHER FORECAST
We usually use the 10mb level to view the polar vortex of the stratosphere. This is approximately 28-32km (17-20 mi) in altitude. This altitude is considered the middle of stratosphere. It gives a good representation about the general dynamics of stratospheric vortex and its downward link.
The strength of the polar vortex can be measured by the strength of its winds. Usually, this is done is by measuring the zonal (west to east) wind speeds around the polar circle (60°N latitude). Below is an ensemble forecast for 10mb winds.
Notice how the polar vortex is at the 10mb level, which is actually stronger that normal for this time period. It is expected to remain strong with minor oscillations. It isn’t record-breaking but it does spin faster for this time of year.
An interesting trend can be seen in the pressure anomalies observed over the polar regions over the past three months. The next image shows pressure anomalies from surface to upper stratosphere.
The strong low-pressure buildup observed in the stratosphere in November can be seen. It was a strong, polar vortex connecting easily to the surface levels in December. But lately, strong high-pressure anomalies have emerged around and over the polar circle, which fight back against the stratosphere, “disconnecting” the upper and the lower polar vortex.
The latest polar Vortex map shows that the stratospheric is in a good place. It doesn’t have the classical circular appearance and appears more oval in shape. However, it is surrounded by a strong wind field. There is a semi-persistent area of high-pressure in the North Pacific. One in the North Atlantic presses against it, creating its oval shape.
The temperature profile at this elevation shows that there is a wide cold-core in the Arctic. This cold-core extends also into North America, Scandinavia, and North America. The high pressure in the North Pacific can be seen, along with some temperature anomalies around its cold core. This is still a stable Polar Vortex.
The polar vortex’s upper and lower edges may seem disconnected, but they are still part of a larger area of circulation. Although the exact core energy may not be strongly connected, its shape can reflect both levels.
You can see this clearly if you look at the most recent 5-day forecast of pressure anomalies in the Northern Hemisphere. You can see the longer profile of the lower-polar circulation. It is also being compressed by the Pacific and North Atlantic. This is what is actually reflecting up into stratosphere.
This is a significant disruption to the lower-level polar circulation. Below is the temperature forecast for the same period. It shows cold air anomalies in eastern Canada as well as the eastern United States. This is due the northerly flow at the backside the low-pressure area to the east, while a higher-pressure system brings warm air into the west.
Looking closer at North America, it is evident that the coldest air is located at the end of the week and will move over the country by the middle of next week. In the northeastern United States, colder weather is possible.
This cold air passage will also bring a fair amount of snowfall. The cold air moving over the Midwest, across Ohio Valley and into parts of eastern and northern United States is expected to bring snowfall.
PRESSURE RISES OVER THE WEST
The pressure patterns will change a little over the next week, with a significant shift in western North America. The area of rising and expanding high-pressure over Alaska and western Canada can be seen below. The ridge is moving up towards the Polar Circle.
This promotes a northerly wind flow from the polar regions, and deepens the low-pressure over eastern Canada. This wind flow is seen in the upper levels of the jet stream forecast. This is also known as the cross polar flow. It tends to bring colder temperatures into North America from the northern regions.
The temperature forecast for this time shows an accumulation of colder air over Canada before being transported down to the eastern and central United States. Warmer than normal air is moving into the polar regions via the Siberian sector. It replaces the colder air that is moving out.
So where does this leave the polar vortex? The high-level, stratospheric polar vortex loses some of the circular forms it had during this period. The image below shows its extended connection to North America. The image’s level can be seen at 30mb. It is approximately 23km/14miles high. Weatheriscool.
This is especially evident in the 3D structure. The polar vortex’s shape is elongated across all atmospheric levels. It also extends down into eastern Canada. It does show how the Polar Vortex’s core structure and low-pressure area are connected.
This connection can also be seen in the vertical pressure anomaly profile. We can see the stratospheric low pressure anomalies that extend down from the stratosphere to lower levels with a direct connection at the -60 to 90 Longitude. This is exactly where you will find the system over eastern Canada.
The pressure anomaly map of North America clearly shows this low-pressure system. We now know that, despite the lack of connection and influence from Polar Vortex’s Polar Vortex, this area is connected upwards. It is therefore considered one of core parts of the lower Polar Vortex. It maintains cold northerly flow to the continent and down into America, thanks to high pressure in west.
The colder airmass is expected to move down from Canada, over the Midwest, and into most of the central and eastern United States. Below is a temperature anomaly forecasted for next week. This shows one of the likely weather situations. The cold air is expected move towards the East, keeping the western United States in relatively normal to warmer conditions.
The snowfall for this period is less than in the first weekend. This is due to the absence of moisture. The cold air will also be very dry. Below is a 5-day forecast of snow depth change.
We can see the snow covering melting across the Ohio Valley. It was dropped this weekend. There will be some snowfall, and snow depth increases, over the Midwest, Great Lakes Region, and the northeastern United States. These numbers are low because this is an ensemble forecast and shows an average of many scenarios.
CROSS POLAR FLOW CONTINUES
The pressure patterns will remain through the end of the month. The strong ridge above Alaska will rise further towards the north, stabilizing cross-polar flow into North America. The low-pressure system that is over eastern Canada will cause the North Atlantic to become a stable feature. This will allow for colder air to flow into Europe through the high-pressure zone.
On the temperature forecast, you will see warmer anomalies over Alaska as the ridge pushes further north. This forces the colder air from the polar regions down into Canada and the United States. Due to the higher pressure in the western United States, the southwestern States are expected to experience warmer than usual conditions.
The stratospheric portion of the polar vortex is still elongated and extends into eastern Canada. This reflects the lower structure. The image’s level is at 30mb. This is approximately 23km/14miles in altitude.
The profile of the vertical pressure anomaly demonstrates that the connection between the stratosphere, the lower pressure area and eastern Canada is sustained. The marked area shows the low pressure anomaly that connects to the stratosphere in the eastern Canada region of -60 to 90 latitudes.
This period’s weather progression is similar to the last, with another round bringing down colder air from the north. Spreading from the Midwest to the central and southern United States, and moving towards east. This “cold train” is the nature of the cross-polar flow, being sustained by the pressure pattern, bringing down waves of colder weather.
Below is the snowfall forecast for the 5-day period of late month. It shows an increase in snowfall and depth over most of the eastern United States, particularly the northeast. You can see the evidence of lake-effect snow in the Great Lakes region. There are also signs of snow in parts of the southern United States.
It is amazing to see how, despite strong stratospheric Polar Vortex, lower level weather patterns can withstand it and actually benefit from that power to boost colder air transport.
The 16-day ensemble forecast below shows this cold train for Boston, the northeastern United States, and Minneapolis, the Midwest. The graph shows the temperature at the lower levels, where we can see individual cold outbreaks following, creating a “cold train”, due to the cross-polar flow weather pattern.
This is clearly shown below in the official NOAA/CPC 8-14-day forecast for the United States. The eastern half of the country will experience colder temperatures, while the western states will experience warmer temperatures due to the high-pressure zone.
The official NOAA precipitation forecast shows that we are generally much drier then normal. The higher pressure is responsible for the drier conditions in the west. The eastern United States is drier due to the lower pressure. The north-central and far northeast corners of the United States see more precipitation.
FEBRUARY POLAR VORTEX & WEATHER
The ECMWF just released their latest extended-range forecast, so we can also use that forecast to examine some February trends. First, let us examine the Polar Vortex. Below is the forecast for stratospheric, which shows a strong character and stable form with colder temperatures than normal.
The corresponding lower pressure pattern in February shows the higher pressure over the North Pacific, Alaska, and the polar regions. The eastern Canada region is still covered by a broad low-pressure zone, with a gap to the central United States. Europe is seeing lower pressure and colder temperatures.
This is the temperature forecast for North America, with hints at colder temperatures in the Midwest. This is a similar pattern as we are seeing now, with the “cold-train” from the north. However, at this forecast range we are only looking at trends which means that most anomalies are hidden within the average.
We are beginning to notice that the low-pressure region is starting to close over eastern Canada and Greenland towards the middle of the month. This would signal the end of the cross-polar flow, and the return of higher pressure to the southern and eastern United States. This can occur when the entire circulation of the polar sphere is taken over by a strong vortex in the stratosphere.
This period’s temperature trends show that there has been a return of warmer anomalies in the United States, with colder air pulling back to the north. However, this pattern still allows for occasional drops of cold air from north, but not to the extent that it would be visible in the forecast average at the range.
However, a more interesting scenario is emerging in stratosphere towards end February. The ECMWF extended outlook is pointing to a warming event. This could lead to a collapse of the polar vortex, as the sun is slowly returning to high altitudes in the polar regions.
This is something to be aware of as it can have a significant impact on the weather development for the Spring season. We will now look at the most recent seasonal forecast trends for winter-spring transition.
WINTER TO SPRING SUMMER SEASONAL FORECAST
This EMCWF data was not available earlier in the month and does not likely cover any possible stratospheric heating/collapse events. The long-range forecast is for the period February-March–April (FMA).
The long-range stratospheric forecast from the same data shows this. It also shows the higher strength of the upper pole vortex. It is possible to see the seasonal weakening, but not any signs of a premature breakup event. This image could look a little different in the next update which is expected to be available in early February.
The strong high-pressure system that is forming in the North Pacific is still forecasted, according to the most recent data. It is likely that this system will continue to be present well into the Spring season due to its global large-scale effects. The jet stream is curving into the North Atlantic and the northwestern United States because of the lower pressure in Canada and Greenland.
Lower pressure over Greenland helps maintain the jet stream further to the north. This allows for an expansion of the high-pressure area over most of Europe.
This is evident in the global airmass temperature, where we see a strong cold lake in western Canada. It has been formed over the past month and is expected to continue into the Spring season. You can see the warmer temperatures in Europe. This would indicate a shift to a more westerly flow into February 2022.
If you look closely at Europe, you will see that the temperatures are generally higher than normal in the north and northeast. However, the warm anomaly is weaker in western Europe. This indicates that colder air intrusions may continue into central and western Europe.
Similar to December, but with reduced frequency. These forecasts are only indicative of the prevailing or average picture for 3 months. This is often a large range of sub-seasonal variations.
We can see the large cold pool in Alaska and Western Canada over North America. This is due to the strong high-pressure area in the North Pacific. This pattern can allow cold air to rapidly spread into the Midwest and central/eastern United States.
Looking at the global precipitation forecast quickly, we see mostly dry conditions over Europe, with a high pressure system, and wetter weather in the north.
North America is seeing more precipitation than western Canada. This region is still experiencing snowfall. In the northeastern and northern parts of the United States, there is more precipitation. The conditions are expected to be normal to dry in the southern United States.
Contrary to the ECMWF model forecasts, we also include the forecast from CFSv2 (run by the NOAA/NCEP, the United States). It shows a similar pattern with the large cold pool in west Canada reaching down to the northwestern United States. The country’s southern part is expected to remain warmer than usual.
Precipitation forecasts show wetter conditions in the eastern United States, as well as parts of the northern United States. The snow can still form in the northern areas of the country due to the cold pool in western Canada. As we get deeper into spring, this option gradually decreases.
As new forecasts and data become available, we will provide regular updates on weather developments. So make sure to bookmark our page, and also, if you have seen this article in the Google App (Discover) feed, click the like button (♥) there to see more of our ForecastsCheck out the latest articles Weather Nature in general.
2022 Weather Forecast – New anomalies are developing in the Atmosphere, the Oceans, which will change the weather patterns as the year progresses.
Source: Severe Weather