The North Pacific’s strong High-Pressure Blocking System is developing. It will be extended into the Arctic Circle by its next push, allowing the polar stream to expand further south and west over the United States in 2022. This transitional period will allow colder weather to make its way from Canada into the central and eastern United States.
These pressure changes were discussed in previous articles. There are some very strong weather drivers behind these pattern “evolutions”, that command the weather patterns each winter season. But why is the strong North Pacific blocking pattern there? It is also why it has been so persistent this winter season.
You will soon discover that the weather is more global than you might think. As we approach the 2022 season, you will quickly discover which two global weather drivers play a significant role in weather pattern development.
DIFFERENT CASES OF WINTER WEATHER
We tend to focus on the larger-scale background of the weather, regardless of whether we are looking at the winter forecasts or the changing weather patterns. This means that we need to identify a strong global weather driver, and its signature, if one exists. The La Nina in the Pacific Ocean has been the primary large-scale weather driver for this year.
For normal day-today forecasts, however, we need to consider the short-term variability. Other than the La Nina, which we will briefly cover below, there are many other factors that shape global weather on different scales and time frames.
Below is an example from a climate survey. It shows different weather phenomena and how they rank on time and size. Large-scale factors such as the ENSO and trade winds are often the main drivers of weather events that occur over long time periods. But as we go to smaller sizes and shorter time scales, there is influence from frontal systems hurricanes, thunderstorms, etc,…
These smaller scales are more difficult to account for in weather models. They are often the main source of weather variability in forecasts and in actual weather. We can still see that the global background global anomalies have an influence on the overall motion and movement of weather systems.
We will show you how two large-scale drivers are influencing the weather and how it changes over time. Their influence is not only seasonal but also weekly, so we will continue to feel them in January 2022.
ENSO IN PACIFIC
ENSO stands for El Nino Southern Oscillation. That is short for “El Niño Southern Oscillation”. This large region is located in the tropical Pacific Ocean. It changes between a warm or cold phase, known as El Nino and La Nina.
ENSO has a major effect on the tropical convection (storms), as well as the complex interaction between the atmosphere and ocean. Long-term pressure changes can be observed in the tropics when ENSO shifts into a warm phase or a cold phase. These changes can have a significant impact on circulation around the rest of the globe, although they take some time.
The image below shows ENSO regions in tropical Pacific. We focus mostly on the combination regions 3 and 4. This is known as the Nino region 3.4. Region 3 includes the eastern tropical Pacific, and region 4 the central and western regions.
Each ENSO phase has a different impact on the pressure and weather conditions in the tropics. This affects the global circulation, which creates a unique weather response around the world. A particular phase (cold/warm), usually occurs between late summer and autumn and lasts until the next spring. Some events are more powerful and can last up to two years.
The ENSO phase that is cold is La Nina while the phase that is warm is El Nino. Their names literally translate to “the girl” from the La Nina, while El Nino translates to “the boy”, indicating an opposite dynamic between the two phases.
The main difference is not only in the temperature, but also in the pressure state. An El Nino is when the pressure over the tropical Pacific is lower with more rain and storms.
However, during a La Nina, the pressure above the equatorial Pacific rises, creating stable conditions and less precipitation. This affects the global circulation and the jet stream in both Hemispheres.
You can see the differences in the pressure patterns in the image below, as well as the difference between the ocean surface temperatures during each phase.
Below is the NOAA’s most recent global ocean temperature analysis. The strong cold anomalies found in the tropical Pacific Ocean’s La Nina phase can be clearly seen. The strongest cold anomalies can be found in the eastern region, going down to 3°C below the long-term average. The current event is a moderately-strong cold phase.
This video animation shows how the cold phase developed between Summer and Fall. It shows the equatorial ocean cooling starting in July, as the cold “waveforms” develop across the equatorial Pacific. They form because the surface water is being pushed to the west by the winds, bringing deeper and colder waters to its surface. These winds also indicate the change in the patterns of tropical pressure.
The combined/consolidated forecast from NOAA/CPC calls for the La Nina to last over the winter and into early Spring 2022. This is a fairly typical scenario. The neutral state will shift during the warmer parts of the year. The development of a new phase tends to occur in late summer and early fall. A warmer phase may develop into the late 2022, which is when we can expect a higher probability.
Below is an image showing the average winter pressure pattern for multiple La Nina winters. The main feature of the image is the strong high-pressure blocking system over the North Pacific and low pressure above western Canada. This is the typical sign of the cold ENSO phase. It pushes the jet stream into the northwestern and northern areas of the United States.
The changing pressure patterns over the tropics, and also over the west Pacific or Asia, support a long-lasting high pressure system in the North Pacific. If ENSO is warm, the North Pacific would be dominated a persistent low pressure system.
If we look closely at the La Nina weather sign below, you can see the strong and persistent high pressure system in the North Pacific. This usually causes the jet stream to shift from western Canada into the north United States, creating a colder/warmer south weather pattern in the United States.
Alaska, western Canada, the northern United States, and Alaska are more cold than normal winters, with more snowfall (and precipitation). The winter season in the south and southeast United States is usually warmer and drier.
We will now shift from a seasonal to a shorter-term scale. We will still remain global, just moving from the ocean up to the atmosphere.
MJO ATMOSPHERIC WAV
The atmosphere in the tropics is quite different. It works in tandem with the Ocean. Invisible wave-like features in our atmosphere are responsible for a lot of the tropical variability. Madden-Julian Oscillation, also known as MJO, is the dominant source of short/medium term variability.
What is the MJO wave? This is an eastward-moving disturbance, or wave, of thunderstorms, clouds and rain, winds, pressure changes, and wind. It can travel around the entire planet, crossing the Equator in 30-60 days.
It can have an impact on the weather patterns further north than the North Hemisphere. This is because there is strong correlation between the tropical pressure variations and the global weather.
The MJO has two phases. One is the enhanced rain (wet) and one is the suppressed precipitation (dry) phases. The graphic below is from NOAA climate and shows the basic components. We have seen an increase in storms, rainfall (lower tension) and a decrease in storms and drier conditions (higher Pressure) on one side and the opposite. Image by NOAA climate.
This image shows exactly how the wave travels along the equator. The tropics are marked by dry/wet anomalies. The green color indicates lower pressure and more storms and precipitation, while the warmer colors indicate less precipitation and greater pressure. This allows us to see how the MJO wave moves through the tropics.
It is important to remember that this wave is stable enough to be broken down into phases. Each wave has a different impact on the global weather. It is important to track how it is moving around the globe.
The pressure changes that it brings can have a greater impact on one region than the others, causing downstream and upstream effects on the rest. This is how the effects of these anomalies translate into global weather patterns.
According to ECMWF, MJO will continue to be in phase 7 through the end of January 2022. Below is an example of how a typical winter 7 influence affects the temperature and pressure around the globe.
Below is a composite image showing phase 7 in December. It shows the average pressure pattern. It is obvious that there are two main high pressure systems. One is located in the North Pacific and Aleutians, and one is over Scandinavia and northwestern Europe.
This means lower pressure over Canada, the northern United States and lower temperatures. This is what the cold ENSO phase does as well, as we’ve seen. This means that this phase 7 works in tandem to ocean anomalies, and is the reason why the North Pacific high pressure is so strong lately.
Below is a composite image that shows temperatures. It may be a little more difficult to read because of the contour lines. However, we have colder temperatures in Canada than in the northern part of the United States. This is not a forecast, but a general trend. This signal could be affected by other factors.
This is the weather pattern we will be looking at in the main section of the article, which includes the forecast for December and January 2022. The MJO forecast shows a strong signal for Phase 7, so we should see some of this in the weather patterns.
This means that the MJO and the La Nina in this case can “boost” each other, as they both force towards the same pattern. They both emerge in the tropical tropics at the same time, but they work at different timescales.
This pattern will be reflected in the forecast. We will be watching to see how these winter weather drivers impact our daily lives over the next few weeks. But first, let’s quickly recap the first winter month so far, and take a quick look at the 2021 overall.
DECEMBER and 2021 GLOBAL WEETHER
La Nina was the name of the season’s first month. Canada was affected by a low-pressure system. The North Pacific saw higher pressure. This causes the jet stream to drop over the northern United States, which separates the warm and cold air.
When we look at December’s global temperatures, we can see that there are a lot of sub-polar and Polar regions with temperatures much lower than normal, north of 60N. Greenland is an exception, as it has strong high pressure systems. The United States also has a warm anomaly, which contrasts with the much lower temperatures in Canada.
We can see the strong warm anomalies in North America when we look at December to date. The south-central states are home to the strongest anomalies. They decrease significantly towards the north border. Cold air from western Canada was a frequent source of cold fronts to the northwestern United States.
The entire 2021 year shows an interesting picture. Most of the United States, Canada and other countries were warmer than usual. The most severe cold anomalies were located in Alaska and northeastern Asia. Australia was generally colder than normal, as well as the equatorial Pacific Ocean. Both were due to the La Nina. Europe was mostly neutral overall.
Globally, 2021 did not compete for the title of warmest year. Below is a graph showing the global temperature anomaly progression. We were actually seeing near-normal temperatures in global average at the start of the year. The temperature anomalies started to rise in the second half of the year, but remained below 2020 on the yearly scale.
The La Nina event, which we now understand has an impact on global weather patterns, can also explain the temperature drop from 2020 to 2021.
WINTER WEATHER PATTERN FORECAST – FROM 2021 TO 2022
We can see a very chaotic pattern of pressure patterns in the latest forecast for December’s end. As we have discussed, the North Pacific is home to a powerful high pressure system. Also, we have higher pressure over Greenland than western Europe. A special pattern is observed over the United States. The western half of the country is under low pressure, which brings colder air into the west.
We can see a stark weather contrast across North America. The southwestern United States will see much colder temperatures than normal. It will also cover most of the western United States. Unseasonably warm weather is also expanding in the eastern and southern United States.
The North Pacific pattern will continue to evolve into January. The Arctic Circle will be impacted by the strong high-pressure region that extends from the North Pacific to the Arctic Circle. It will connect with the Greenland high-pressure area. This will strengthen the low-pressure region over western Canada and western United States, allowing it to move across the country with the colder air.
Below is the temperature forecast. The anomalies are located in western Canada. This has been the case for the past few days/weeks. The low-pressure area in the western United States will bring cooler than normal air into most western and southern parts of the country. The transition of the lower pressure system will allow for colder anomalies to extend from the midwest to the northeast.
The 7-day forecast means shows the strong cold air anomalies in the northwestern United States. You will also notice the southeast experiencing much warmer temperatures than normal, which creates the perfect weather opposition.
We see the transition to colder than usual conditions over large parts of the United States, thanks to a strong cold front. It will come from the northwest, traverse the entire country, and then move out into the Atlantic.
We are currently working on a detailed article about the strong cold air outbreak event. Keep checking back.
MID-MONTH WEATHER FORECAST
The pattern continues into the mid-January period. The Aleutians are still under strong blocking high pressure. This is a classic La Nina and the MJO phase 7. It is expanding into the Arctic Circle, but it also keeps the main low-pressure core above Canada and the Northern United States. Ridging continues over the southeastern United States.
The temperature forecast for this period shows that there is a large area of very colder temperatures than normal. The pressure pattern will favorably release the cold air from the east and central parts of the country, as it expands from the northwest United States. These anomalies are significant because they provide a significant lead time.
The Arctic Circle’s high-pressure system pushes the jet stream a little further south and east. This means that there are fewer cold air outbreaks in the eastern and central parts of the United States. Below is an example forecast using the GFS model. It shows a possible scenario that could result from this setup.
As you can see we have a strong cold abnormality expanding from western Canada over the Midwest into eastern United States. This is not a forecast and is only an example of a possible weather scenario that could be created by weather pattern adjustments.
WEEKLY WEATHER OUTLOOK
We will also add the weekly average probability forecast, which is based upon the NAEFS model. This is a combination from weather models from Canada and the United States. It is clear that the solution is very similar, with colder air flowing from the northwest to the eastern United States while the jet stream drops south.
Precipitation-wise it is likely that there will be more precipitation in the northern half than usual. This can indicate more snowfall when combined with colder than usual air.
The 8-14-day forecast for the United States by NOAA is also available. It is based on different models. Below is the temperature forecast from January 2022. NOAA predicts colder temperatures in the northern and western United States. The southern and southeastern states will remain warmer than normal, although to a lesser extent than December.
Below is the NOAA precipitation outlook. This forecast predicts normal to above average precipitation for most of the United States. The high-pressure system is expected to cause below-normal precipitation in the southern states.
The ECMWF’s weekly forecast for January 2022 will allow us to extend our January 2022 weather outlook. We will be looking at the North American temperature anomalies as they relate to January 2022, from mid to late.
JANUARY 2022 ECMWF WESTERN TRENDS
Using the ECMWF Ensemble Forecast, we can see deeper into January. This is the ECMWF extended prediction system. It is run twice per week.
We can see that the North Pacific is still the dominant high-pressure area and Canada’s low pressure are continuing into the middle of the month. This “lockdown” pattern keeps the warm/cold temperature extremes divided into southern/northern United States.
You can see this in the temperature forecast. Canada and the United States are still experiencing colder than normal air. The southern states are much warmer than usual. The exceptions are the northeastern, central, and eastern states. There is a neutral zone, which indicates a possible transition of cold fronts over the midwest and eastern United States.
The pressure pattern will not change much in the last month. Global weather drivers are likely to remain the same. However, we do see a low pressure extension further north into the northwest United States.
Temperature-wise we see a similar trend. It is colder than usual in Canada and the United States’ northern regions, and it is warmer in the south. The neutral one is still visible over the eastern and central parts of the United States. This indicates the likelihood of colder air from the North. The west United States will also be expected to be colder than usual.
EARLY 2022 WINTER PATTERN
We will quickly examine the seasonal trends for the early 2022 using the ECMWF long range forecast. The period in question is the January-February-March season, so the first meteorological Spring month is included in the forecast. However, March’s signal is usually weaker than that from the average because the winter months have stronger patterns.
This forecast includes the most recent data and was published earlier this month. The strong high-pressure system of the North Pacific is still visible as you can see in the forecast pressure pattern. This is the sign of the La Nina, and it is likely to continue well into the Spring season. The jet stream is being shaped into the northwestern United States because of the lower pressure found over Canada.
The strong cold pool in western Canada is evident when we look at the global airmass temperatures. This month, the cold pool has formed and will continue to form until the end of winter season. The warmer temperatures across Europe are a sign of a change in the pattern to a more western flow after the December that was colder than usual.
If we look closer at Europe, we see that the surface temperatures are mostly higher than normal in northern Europe. There is however a neutral area in central Europe which suggests that colder air intrusions may continue in January or February. Long-range forecasts, however, only show the average or prevailing picture for 3 months. This can be subject to a lot of variations.
The large cold pool is visible over North America. It can be seen in western Canada and Alaska. This is due to the strong high pressure over the North Pacific that causes the north flow. This pattern allows cold air to quickly spread into the Midwest and the central United States. We have seen this happen in January 2022 forecast. It is unlikely that it will be frequent enough to skew seasonal average.
If we look at the global precipitation forecast quickly, we see that Europe is experiencing drier conditions than normal due to higher pressure. Canada will see more precipitation in North America. As is normal in such a pattern, more precipitation is forecast for the northwestern and northeastern United States. The weather in the southern United States is expected to be normal or drier than normal, as expected for a La Nina-weather season.
Below is the official temperature forecast for the United States from NOAA for the Jan-Feb-2022 season. It shows the temperature chance, with equal chances for the northern United States. The northeast and southern half of the country have a higher chance of experiencing warmer than normal weather. This is what we saw in the long-range outlook above.
However, such a pattern still allows for strong cold-air outbreaks into the Midwest and central states. The western Canadian cold pool will be strong and ready to send cold air into the United States once the pressure pattern swings.
The official precipitation forecast supports the models. We see a higher probability of more precipitation (and snowfall in the northwestern and northeastern United States. The active cold ENSO phase will make 2022 the drier year for the Southern United States.
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Source: Severe Weather