Winter 2021/2022 is officially over. We will be looking at the many cold- and warm-related anomalies that have affected the United States, Europe and the rest of the world. We will also look at what the main driver was for this winter’s weather and how accurate the winter predictions were.
To try and understand the Winter season and its forecast, we must realize that there is no “magic bullet” when it comes to weather. Global weather is complex, with many factors that affect it on a large and small scale.
There was one major oceanic driving force in this Winter season that is still active into Spring. We will examine its progress, how it will translate into Spring 2022, and look for hints as to its impact on the next Winter season 2022/2023.
COLD LA NINA IN OCEAN
ENSO was a key driver of the winter season. That is short for “El Niño Southern Oscillation”. It is located in the tropical Pacific Ocean and changes between warm phases in the equatorial sea. Usually, the phase change occurs in about 1-3 years.
Below is an image showing all ENSO regions in the. The main regions 3 and 4 cover a large area of the tropical Pacific. The main region, designated Nino 3.4, is the focus of analysis and forecasts.
ENSO has a significant influence on tropical rainfall patterns (storms), and the complex exchange between ocean and atmosphere. With each new phase, large-scale pressure changes can be observed in the tropics.
Below is an image from NOAA Climate that shows typical circulation during a negative ENSO event. The eastern Pacific is experiencing a drop in air pressure, which creates dry and stable weather conditions. Contrarily, air rises to the west Pacific, causing frequent thunderstorms as well as a lot of rain in the west Pacific.
ENSO’s influence on the tropical convection patterns, and consequently the ocean-atmosphere systems, is significant. It exerts its influence worldwide through this delicate ocean/atmosphere system.
A specific phase (warm/cold), typically develops in late summer and early fall and can last until next year, or up to two.
The cold ENSO phase (La Nina) is called El Nino, while the warm phase (El Nino) is called La Nina. Other than the temperature differences, the major difference between the phases is also the pressure state.
Below is an image that shows the ocean surface temperature and the pressure pattern differences between the warm and cold phases.
An El Nino is when the pressure in the tropical Pacific is lower and there are more storms and rainfall.
However, during a La Nina, the pressure above the equatorial Pacific rises, creating stable conditions and a lower precipitation. This affects both the Northern and Southern hemispheres, and it also impacts the global circulation.
The ENSO 3.4 region is the focus of the image below. It shows how the ocean temperatures fell in Fall 2021, which was the beginning of the La Nina. It has now slowly fallen into Spring after reaching its maximum temperature in Winter.
Below you will see the global ocean temperature anomaly of the Winter season 2021/2022. The strong cold anomalies can be seen in the tropical Pacific Ocean due to the La Nina phase.
Combining the 13 most powerful ENSO events can give us a rough idea of their main weather influence. As you can see, the main feature in a La Nina winter’s is a high-pressure system over the North Pacific and low pressure above Canada.
The strong high pressure system encourages the development of low-pressure regions over Alaska and Canada. It causes the jet stream to curve downwards between the pressure systems.
As the jet stream leaves North America, it has to deal first with the North Atlantic pressures. We do not have any clear signals over Europe. Here, the overall influence of the Polar Vortex circulation plays a greater role.
The image below shows the North American winter pattern. It shows the average position and the corresponding weather patterns of the jet stream during La Nina winters.
The curved jet stream brings colder, more stormy air from west Canada into the northwestern United States. It also brings warmer, drier weather down to the southern regions of the country.
This can significantly change the jet stream pattern that exits into the North Atlantic, affecting the winter weather in Europe.
Now that we know the causes of winter weather patterns, it is possible to look at the seasonal analysis of Winter 2021/2022. Next, we will examine how these same weather drivers will transition into the weather patterns in Spring and early summer.
RUNDOWN WINTER 2021/2022
The coldest three months of the year are December, January, or February. Summer covers the three warmest months: June, July and August.
The transitional seasons between the warmest part of the year and the coldest are Spring and Fall. This means that meteorological seasons cover the entire year. However, they are based on only the coldest and most warmest parts.
This is slightly different than the astronomical Winter. When looking back at a season of weather, we always use the official meteorological times, as these are the official statistics.
First, we will break down the Winter season monthly. We will then look at the total seasonal average, before we dive into the forecast portion of the article, which looks at Spring and early summer 2022.
DECEMBER 2021: WINTER WEATHER ALYSIS
December is the first month in the meteorological winter seasons. It began under the strong influence from the La Nina. The pressure pattern image below shows that there is a strong high-pressure area in the North Pacific.
This is a classic weather response to La Nina. This blocking high resulted in a drop in pressure over western Canada and an increase in pressure over the southeastern United States. A ridge was rising over western Europe, which brought down colder air to northeastern Europe.
If we look closer at Europe, we can see the cold air above northeastern Europe. The rest of the continent was much more comfortable than normal.
North America was witnessing a much more dynamic pattern. There is a stark contrast between unusually low temperatures in western Canada and high temperatures in the southern United States.
This is the expected temperature reaction to a La Nina. It was strong in December. Records were broken in Canada’s western provinces, while records were set in the south.
Precipitation-wise, we will be looking mostly at the snow, as that is the form of precipitation typically “most wanted” during the winter season.
Below is the December snow depth anomaly. First, we can see the low snow cover across Europe. Northeastern Europe saw snowfall that was above-average due to the cold air. We saw snow cover at higher elevations in central Europe.
As expected, the temperature picture shows a North American snow depth anomaly. The absence of snow cover was evident in most of the southern and eastern United States. Northern California and Nevada had snow depths above average, as well as parts of western Canada and southeastern Canada.
JANUARY 2022 WINTER WEETHER ANALYSIS
The pattern slightly changed from January to February. Although the La Nina high-pressure area in the North Pacific is still present, it moved further to the northwest. A separate high pressure system formed over America’s west coast.
The west coast high has paired up with the low-pressure system in eastern Canada. It has brought the jetstream down into the eastern United States. This has also helped to maintain a stronger high pressure system in the North Atlantic that reaches into western Europe.
We can see a very different picture when we look at the temperatures in Europe than in December. Under a northerly flow, we can see colder air intrusions in western Europe. Over the rest of the continent, temperatures were generally warmer than normal.
Over North America, a huge temperature reverse was observed. The cold pool has moved to eastern Canada and the jet stream has extended down into the eastern United States. This has maintained a colder northerly flow towards the Midwest and northeastern United States.
The high-pressure system had caused temperatures to rise in the west United States and Canada.
If we look at the snow depth in January, it is similar to December. The Northeastern Europe received more snowfall than normal. Due to the lack of moisture (dry airmass), there was less snowfall in Europe than usual.
The colder air source has caused snow to extend in North America. The snowfall levels in the western United States are much higher than normal.
FEBRUARY 2022: WINTER WEETHER ANALYSIS
February’s pressure pattern saw another adjustment. It is evident that the high-pressure systems has intensified over the west coasts of the United States and Canada. This brings the jet stream back down into the United States, though slightly further west.
The North Atlantic witnessed a strong positive NAO trend. This means that most of Europe is experiencing strong westerly flow.
It is evident in the temperature anomaly analysis. There were some severe anomalies in February, particularly in the eastern regions. The monthly average was higher than usual because there were fewer colder air intrusions.
The month of January is quite cold across North America. The strongest cold anomalies have moved further west, covering central Canada as well as the northern United States.
The average monthly temperature in the United States was a lot lower than the normal. California, Oregon, and the southeastern United States are the exceptions.
Despite strong warm anomalies in the northeastern Europe, we still had more snowfall. Most of central Europe saw snowfall below-average.
Below you can see that snow cover was stable in the Midwest and northeastern United States. This is a monthly average. Some events that drop snow for a few days may get lost in the average.
It was still snowier than usual in parts of northern and northeastern United States and western Canada. In the northwestern United States, snowfall was much lower.
Now we will combine all winter months and compare the seasonal average to the forecast before winter began.
WINTER 2002/22 FINAL WEETHER ANALYSIS & FORECAST
We will be reviewing the November forecast, which is the last month of Autumn. The forecast from the ECMWF model is used, as it is usually deemed as the most “reliable” long-range model. It can also have its bad and good seasons.
The forecast (and analysis) is centered on the December-January-February seasonal period, designated as DJF on the graphics.
Below you will find the ECMWF global pressure anomalies forecast. The strong high-pressure seen in the North Pacific is a result of the La Nina. A natural response to this is a low pressure over Canada and the jetstream riding in-between.
It was located in a low-pressure zone over the North Atlantic, and high-pressure over most European countries, with the exception the west.
The model did a great job over North America. The high pressure area over Canada can be seen clearly, as well as the North Pacific’s high pressure. This was made easier by the La Nina background forcing.
It had a worse idea than Europe, with a nearly reversed pressure anomaly pattern. High-pressure was dominant in the west and low pressure in the east.
We use the 850mb temperature level for global temperatures. This is approximately 1.500m (5.000ft) which is a good representation for the airmass.
According to the forecast below, the ECMWF had forecast a strong cold lake over Canada, which would then be bordered by the northern United States. The Southern United States was forecasted as being mostly under normal airmass. This is also true for Europe.
Again, the forecast for North America was very favorable. The strong cold pool is visible over Canada and into the United States. A warmer anomaly can be seen in the south.
Europe was mostly warmer than average in its central and western regions. It was neutral to colder in the eastern parts of Scandinavia and the east.
However, the actual surface temperatures we feel can be different from the raw anomalies in the airmass. Below is the winter average seasonal picture. The average temperature for Europe was much higher than normal.
It was a different story with the surface temperatures over North America. This is where the strong cold anomaly over Canada really shines through, and extends into the northern United States. The rest of the United States was generally warmer than normal. This is due in large part to December’s unusually strong warm anomalies.
Looking at the total winter snow depth, it is clear that there was more snowfall in the northeastern regions than on mainland Europe.
The entire season in the United States saw a decent amount of snow. Some parts of the United States saw more snowfall than usual, as did the higher elevations in California and Nevada.
The global precipitation forecast shows that Europe is mostly neutral with more precipitation in the northeast. The ECMWF winter prediction for North America predicted more precipitation over Canada, and the northern United States.
The southern United States was expected to see less precipitation. This is a typical La Nina distribution of North American precipitation.
We can see that there is more precipitation in north-central Europe and northeastern Europe if we look at the actual precipitation anomalies. Conditions were more dry in western and southern Europe.
The ECMWF winter forecast for North America was more accurate. Canada and the Ohio Valley saw more precipitation than in other parts of the United States. The conditions were mostly dryer than normal in the southern and central United States.
Overall, the ECMWF model predicted quite well over North America thanks to the active La Nina EnSO phase. It provided a source to the model to draw on.
It performed poorly in Europe because the La Nina influence there is also much diminished. The North Atlantic is the main conduit through which the signal/influence of La Nina is weakened.
NOAA OFFICIAL WINTER MARKET
The NOAA also publishes its annual forecasts for the United States. Once the season is over, they release a verification. Below is their forecast for temperature and precipitation in the United States, along with the verification.
The forecast is on the left, if you look at temperatures first. They called for a La Nina pattern with warmer temperatures in the south/east and cooler in the northwestern United States.
The anomalies were more extreme in the east United States and the south-central United States. In the north and parts of the southwest, temperatures were lower. Overall, it was a positive forecast.
Similar results can be seen for precipitation. For the northwestern United States, the Midwest, and the northeast, more precipitation was needed. While the eastern half of the United States had more success, the majority of the west was less successful than normal.
The Spring is already here. We will be looking at how weather drivers are transitioning from winter to spring, and what the most recent forecast shows for weather development into early-summer 2022.
FROM WINTER TO SPRING
We all know that the La Nina cold oceanic La Nina was a major driver of the winter weather patterns during the 2021/2022 seasons.
Below is the latest ocean temperature anomaly data, which shows that La Nina continues to be present in the tropical Pacific Ocean. You can still see the cold anomalies in that region. They are weaker than winter, but the atmospheric influences can last for a longer time.
The latest forecast by ECMWF shows that the La Nina will weaken and disappear into early summer 2022. This summer, neutral ENSO conditions can be expected.
Based on the forecast and current status of the La Nina we can see that its influence will be felt for most of the Spring season. But there is one more “shorter-term” influence that can’t be denied in the current stages of the Spring season.
The Polar Vortex is basically the polar circulation in the Northern Hemisphere. Before we get into the Spring/early summer forecast, let’s examine the role that the Polar Vortex will play with the La Nina.
THE COLD-SEASON POLAR VORTEX
As we approach autumn, the sunlight reaching the polar regions decreases each year. This is how cooling begins above the north pole.
Despite the drop in polar temperatures, the atmosphere further south remains warm because it continues to receive light from the Sun.
Below is an image that shows the winter solstice. The polar regions receive less solar energy than regions further south, but still receive plenty of sunlight.
However, the temperature is falling in the polar regions and the pressure follows. The temperature difference towards the south is greater when there are colder temperatures than at the pole.
This causes a strong global tension difference and a large low pressure (cyclonic) circulation to develop across the Northern Hemisphere. It extends far beyond the surface layers and into the stratosphere. This is called the Polar Vortex.
The image below shows an example of the Polar Vortex peak strength at around 30km/18.5miles elevation (10mb level) in the middle stratosphere during the Winter season.
It behaves almost like a large cyclone and covers the entire north pole to the mid-latitudes. It is strong at all levels. However, it can take different shapes at different altitudes.
It is basically one large cyclonic region that is spinning across the entire Northern Hemisphere. From the ground up to and beyond the stratosphere, it reaches over 50km/31miles.
The image below shows the seasonal height anomaly in stratosphere for winter season. It can be seen that the polar vortex was running at lower pressure than normal. This allowed for stronger polar circulation.
This can be seen below in the zonal wind speed graph of the Polar Vortex at 10mb. The black line represents the long-term average and the blue line the strength of the polar vortex in the 2021/22 cold seasons. The polar vortex was stronger than usual for most of the cold seasons.
The graph above shows that the polar vortex ended in March. The polar vortex circulation collapsed mid-March, causing disturbances in the circulation for days/weeks ahead.
We created a video showing the 10mb level (30km/18.5miles), development of the polar Vortex collapse. The Polar Vortex is first seen being broken apart, then a strong displacement and weakening.
Below is an image that shows the atmospheric pressure anomalies, which change with the passage of time. The blue color is indicative of lower pressure (stronger the polar vortex). But, notice how the high-pressure is coming down from above the stratosphere over these next days/weeks.
This is due to the abrupt collapse and reorganization of the Polar Vortex. As we get deeper into spring, it will continue to play a key role in the longer-term weather development.
Below is an image showing the average temperature pattern between 0 and 30 days after the collapse of Polar Vortex. High pressure in the Arctic due to the collapse can help to release the cold air from the Arctic regions and transport it into the mid-latitudes in the United States or Europe.
The extended range ensemble forecast for mid April shows a region of high pressure over the Arctic. The two main low-pressure areas are Siberia and eastern Canada/Greenland.
Based on available forecast data, this is a likely outcome scenario from the collapsed Polar Vortex.
We can see that Canada and the north United States have been experiencing colder temperatures in the forecast temperature for the same time period. Under high pressure, Arctic regions remain at higher temperatures than normal.
This pattern is very similar to the expected aftermath for the Polar Vortex collapse, which we have shown above.
We will conclude with the long-range forecasts for the rest of the Spring and early Summer 2022.
SPRING TO EARLY SUMMMER LONG-RANGE OUTLOOK
We will be using the ECMWF long-range model (SEAS-5), as it is often referred to as “the best” model for long-range forecasting. As we’ve seen, it has demonstrated a decent skill for the Winter prediction.
The forecast period that we will be focusing upon is April-May–June (AMJ2022). This period covers the remaining months of meteorological spring, and the first month meteorological summer.
Below, the pressure forecast from ECMWF shows that there is a strong La Nina high level of pressure in the North Pacific. Over western Canada, a low-pressure area is still visible. A larger low-pressure area can be found in the eastern Polar regions.
The global temperature distribution is somewhat similar to past winter patterns. In North America, we see signs of colder temperatures in western Canada and Alaska. These temperatures will transition to the northwestern United States. The Southern United States is expected to be much warmer than normal.
Europe is experiencing mostly warmer than average conditions. There is also a storm track further north from the North Atlantic to northern Scandinavia.
We can see warm anomalies across most of Europe when we look closer. The ECMWF suggests that there is still potential for cooler northerly flows from the northwest to parts of central Europe.
The neutral area extends from Canada into North America. It can be seen in North America. This area is more likely to experience temperatures below normal. However, we also see a weaker warm anomaly region in the Midwest and northeastern United States.
Warm anomalies are a certainty in the Southwest United States. The ECMWF pressure pattern for the southern United States is also consistent with other seasonal forecasts, increasing confidence in the forecast.
The precipitation forecast shows that most of the west United States will experience drier conditions. Some parts of the east United States have higher chances of experiencing wetter conditions. Europe experiences higher precipitation than northern regions because of the higher frequency and intensity of low-pressure systems that move over this region.
This distribution of precipitation is concerning as it is sustaining severe drought conditions over the south, especially the southwestern United States. As shown in the analysis below, the drought conditions are already severe over the south and west.
According to the NOAA official weather outlook, the northwestern United States is more cold than normal. As shown in the model forecast, the likelihood of warmer weather than normal is higher in the eastern and southern United States.
The official precipitation forecast also looks very similar to that of the model forecast. We see an equal-to higher probability of more precipitation for the Midwest and Ohio Valley. The western United States is expected to experience a dry season towards summer.
WINTER SESSION 2022/2023 EARLY TIPS
It is impossible to predict the weather season so far in advance. We can however, look at the overall direction of the development.
We can see the expected trends for the second half of the year by focusing on the ENSO, the strongest weather driver.
Below is the official CPC/IRI probabilistic ENSO forecast. It shows the current La Nina extending into the early summer. It shows mostly neutral probabilities later in the year. There is no El Nino or La Nina developing for the winter season.
Below is a consolidated analysis of forecast images from multiple North American season models. It also shows the La Nina reaching its late spring season. We see a return of the neutral phase (between 0.25 and 0.5) with a slight possibility of an El Nino developing later on in 2022.
The ECMWF extended seasonal outlook also shows that the cold phase will end in Spring according to the most recent ECMWF extension. The forecast spread is high, with the average staying in neutral for the next winter season. An El Nino is more likely than a new La Nina, historically.
But what is the importance of an El Nino? If the ENSO remained neutral, then other global driver would take over, making it unpredictable for winter. However, even a weak El Nino could develop and provide guidance for weather development.
We have a strong, persistent low-pressure area in North Pacific during the El Nino winter seasons. This pushes the polar stream further north, bringing warmer flows to the northern United States of America and western Canada. The southerly Pacific jetstream is amplified, bringing more precipitation and cooler weather to southern United States.
The average snowfall for an El Nino winter is much lower than the La Nina. The El Nino seasons bring less snowfall to the northern United States. Snowfall is limited in the north because it is usually warmer than normal and drier that normal.
However, snowfall is higher in the west-central United States as well as in parts of the east United States. There are cooler temperatures and more moisture.
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Source: Severe Weather