New forecast data for Winter 2022/2023 shows a strong weather presence of the final La Nina phase. A blocking system is forecast to develop over the North Pacific, altering the jet steam and the winter weather patterns in North America. Temperature, pressure, and snowfall patterns will be affected as the ocean anomaly alters the atmosphere.
Many factors are influencing the Winter season each year. But this year, one of the main factors is the cold La Nina in the ENSO regions of the equatorial Pacific, entering its final year of dominance.
But how can the oceans have such an impact on winter weather? We will quickly examine how La Nina works and how its influence from the past can show us the future weather development as the Winter season 2022/2023 is about to begin.
WINTER BETWEEN THE OCEAN AND ATMOSPHERE
La Nina develops in the ENSO region, which is short for “El Niño Southern Oscillation.” This region of the equatorial Pacific Ocean changes between warm and cold phases. Typically there is a phase change around every 1-3 years.
The cold phase is called La Nina, and the warm phase is called El Nino. We are currently in a La Nina phase, entering its 3rd and final year, which is a rather rare occurrence.
The image below from NOAA Climate shows the typical circulation during a cold ENSO phase. High-pressure and sinking air is found in the eastern Pacific, promoting stable and dry weather. At the same time, the air rises in the western Pacific, with lower pressure and more precipitation.
By changing the tropical weather patterns, ENSO significantly impacts the ocean-atmosphere feedback system. Through this ocean-atmosphere system, the ENSO influence spreads globally.
Looking at the latest global ocean anomalies, you can see the cold La Nina standing out in the tropical Pacific ocean. The rest of the world shows warm pooling in the North Pacific. But a cold pattern is emerging along the west coast of North America, and some cooling is seen in the North Atlantic.
Below we have a close-up view of the tropical Pacific Ocean analysis. We can see the cold anomalies in the marked ENSO regions. The currently active La Nina is entering its third-year phase, extending the cold ocean anomalies across most of the tropical Pacific.
La Nina forms during strong easterly trade winds, which can tell us much about the general state of global circulation. This way, we can use these anomalies as an “indicator” to know the current state of the global climate system.
Below, you can see the progress of some historical multi-year La Nina episodes, with only two cold events previously also developing a 3rd-year event. Three events went neutral in the third year, and three phases reversed into an El Nino in the third season.
To better understand the ENSO development, we produced a video showing the ocean temperature anomalies from Summer to Fall 2022.
ENSO cooling restarted in August as the cold waves developed across the equatorial Pacific. But it intensified further in September as the easterly trade winds got stronger.
LA NINA SEASONAL FORECAST
Below we have the latest analysis/forecast graphic by ECMWF, which shows the forecast of the main ENSO region (Nino 3.4). The La Nina conditions (below -0.5 anomaly) will prevail into Winter. But a weakening of the La Nina is expected for early next year, with a warm phase increasingly likely later in the year and in the next Winter season.
Looking at the IRI probability forecast, we can see a high agreement for the cold phase lasting over the Winter season. A breakdown of the cold phase is expected as we go into next Spring, with a warm phase (El Nino) increasing in probability later in the year.
The combined multi-model ocean forecast shows the cold anomalies in the Pacific regions over the Winter season. A stable La Nina is forecast on all long-range systems, giving high confidence also for its large-scale weather influence.
MODIFIED WINTER JET STREAM
Typically, the first influence of these ocean anomalies can be seen in the changing jet stream patterns. The jet stream is a large and powerful stream of air (wind) at around 8-11km (5-7mi) altitude. It interacts with pressure systems and affects their path and evolution.
The jet stream is an important piece of this forecast. It is one of the main ways La Nina can more directly influence the weather patterns, especially over North America.
Historically, a strong high-pressure blocking system in the North Pacific is the most common effect of a cold ENSO phase. That usually redirects the polar jet stream down over the northern United States.
The image below shows the combined (average) pattern during the last few La Nina winters. We can see a strong high-pressure system in the North Pacific and a low-pressure area over Canada and southwestern Europe.
The circulation of the strong high-pressure system promotes the development of a low-pressure region over Canada. That curves the jet stream downwards in between the two pressure systems, bringing colder air into the northern United States.
Looking at the temperature analysis for the same winters, we can see a cold anomaly under the jet stream in western Canada and the northern United States. Warmer than normal winter prevails in the southwestern and southeastern United States and eastern Canada.
Precipitation-wise, La Nina winters are usually drier over the southern United States. Drier conditions also develop in the southeastern United States as La Nina produces a weaker subtropical jet stream and less moisture over the southern United States. More precipitation is typical over the northwestern United States, the Great Lakes, and parts of the northeast.
The image below shows jet stream re-position over North America in a La Nina Winter. You can see the average position of the jet stream and the resulting weather patterns, with colder air focused over the northern United States and western Canada.
The shifting jet stream brings colder temperatures and storms from the polar regions down into the northern and northwestern United States and warmer and drier weather to the southern parts.
In the northern part of the country, colder and wetter events are more frequent, as the jet stream directs the storm systems that way. But that can somewhat lockout the southern United States, creating warmer and more stable weather with less frequent storms and cold fronts.
As the colder air is more easily accessible to the northern United States, it also helps to increase the snowfall potential. Areas like Alaska, Canada, and the northern/northwestern United States typically benefit from more snowfall in a cold ENSO phase. The graphic below is provided by NOAA-Climate.
WINTER SEASON 2022/2023 – NOVEMBER FORECAST UPDATE
You now know what the La Nina weather influence will be this upcoming Winter and how it usually impacts the jet stream and pressure systems. We will now look at the actual model forecast, freshly updated this month, and the latest trends for Winter 2022/2023.
In this update, we focused on three seasonal models. The ECMWF from Europe, the CFSv2 from the United States, and the North American NMME project. Graphics are from the Copernicus Climate project and the CPC/NCEP.
All these forecasts are an average picture over three meteorological winter months (December-January-February) and show the general prevailing weather patterns.
Even if the models were 100% accurate, it does not mean that such weather conditions would last for three months straight. It only suggests how the weather patterns might look most of the time.
ECMWF LATEST WINTER SEASON FORECAST
The latest winter pressure pattern forecast from ECMWF below really amplifies the La Nina high-pressure system in the North Pacific, extending to the western/southern United States. A low-pressure anomaly is forecast over western Canada as expected, bringing the jet stream into the northern United States.
We also see the North Atlantic in a weak negative North Atlantic Oscillation (NAO) mode. Also, a low-pressure area over southwestern Europe and the Azores, opening several different pattern variations throughout Winter.
The global airmass temperature forecast shows the typical cold ENSO pattern. Western Canada and parts of the northern United States are seen with colder to average temperatures. Warmer anomalies are forecast over the western and southern United States.
Europe shows warm anomalies over the central and northern parts, with the influence of the nearby low-pressure area in the southwest. We have observed high variability over the continent in each run, proving the low-confidence of the La Nina impacts in Europe.
Looking at the surface temperature probability forecast over Europe, we see a warmer pattern. Most of the continent is in the warmer temperature range. However, average temperatures are more likely over the western/southwestern parts.
Looking at the precipitation forecast, we can see Europe having a mostly drier precipitation signal over the mainland. More precipitation is forecast over the Mediterranean and far northern Europe.
Over Noth America, the latest ECMWF forecast shows average to colder surface temperatures over most of western Canada, extending into parts of the northern United States. Warmer than normal temperatures are forecast over the southern United States, with a weaker anomaly going toward the northern Midwest.
A negative NAO usually means a more northerly flow over the Midwest and the eastern United States. We have seen this development in the past in La Nina winters.
In this forecast, we do see a hint of weaker probabilities for warmer anomalies in the northern United States. But it is not yet clear how much of it is due to the negative NAO signal. There are sub-seasonal weather patterns also at work, like the MJO or the Polar Vortex.
The precipitation anomaly forecast for North America shows a more typical La Nina-type pattern over Canada and the United States. More precipitation is forecast over western Canada and the northwestern and eastern United States. Drier conditions remain over the southwestern United States, as usually seen in a La Nina pattern.
ECMWF WINTER 2022/2023 SNOWFALL FORECAST
As always, we produced a special snowfall forecast from the ECMWF data. Over Europe, we see below-average snowfall over most of the continent. This still does not mean there will be no snow, but just indiates less snowfall than normal.
The next image below shows the change in the snow depth forecast between the latest model data and the previous model run. We can see that the latest ECMWF forecast shows less snowfall over most of the continent, compared to the previous run.
Over North America, you can see more snowfall over the northwestern United States and the upper Midwest, and western Canada. Lower United States has less snowfall than normal. But keep in mind that less snowfall than average does not equal no snowfall. So there can still be strong individual snowfall events, despite the forecast showing less snowfall than normal.
Comparing the latest forecast to the previous one, we can see that more snowfall is being forecast across much of the western and northwestern United States, and parts of the lower Midwest. Again, this is a reflection of the pressure changes in the latest model forecast.
We will release a unique forecast article dedicated to latest snowfall predictions. There, we will take a more in-depth look at snowfall potential, including more models and a month-by-month breakdown.
CFSv2 WINTER SEASON FORECAST
CFSv2 is the long-range/seasonal forecasting system from the United States NOAA/CPC. We use it in contrast to the ECMWF, as it is the most widely used seasonal forecasting system in the United States.
Looking at the latest data, the CFS is close to the ECMWF with the strong La Nina high-pressure zone in the North Pacific and a low-pressure response over western Canada. However, the Atlantic pattern is different, as the CFS extends high-pressure belt directly into Europe and shows a positive NAO pattern.
Airmass temperatures are most interesting over North America, with a strong cold pool developing over Canada and warmer air in the southern United States. The jet stream is usually found between the two air masses. Europe is seen as mostly warmer than normal.
The surface temperature forecast shows a really strong dipole pattern over North America. Much colder than normal temperatures are forecast over most of western and central Canada, expanding into the northern United States and parts of the northeast. Warmer than normal Winter is forecast over the southern half of the United States.
The precipitation anomaly forecast for North America shows the main weather dynamics (with increased precipitation) over the northwestern and eastern parts of the United States. Drier than normal conditions are forecast for the south-central United States and the southeast, showing a strong La Nina influence.
We must remember that the strongest weather dynamics usually unfold between the cold and warm anomalies, including snowfall. CFS has no snowfall data, but this temperature and precipitation pattern would suggest more snowfall over the northwestern United States, the upper Midwest, and parts of the far northeastern United States.
NMME WINTER 2022/2023 WEATHER FORECAST
NMME stands for North American Multi-Model Ensemble. It is a special forecast combined from several different North American long-range models. It is useful as it contains different calculations and weather solutions, providing an average forecast from different perspectives.
The ocean temperature forecast shows the active La Nina phase over the duration of the Winter season, similar to other global forecasting solutions. From this, we can expect similar results also in the atmospheric forecast.
Looking at the pressure anomaly forecast, you can see the expected strong high-pressure system in the North Pacific, resulting from the active La Nina. A low-pressure system is over Canada, pressing the jet stream down into the northern United States.
The temperature forecast for North America shows this jet stream pattern. You can see colder temperatures over the northern United States and most of Canada. Warmer temperatures are forecast south of the jet stream, over the central and southern United States.
You can see a similar pattern in the precipitation forecast below, where more precipitation is forecast over the northern half of the United States and Canada. Drier Winter is expected over much of the southern United States, with a weaker subtropical jet stream.
Overall this shows a very textbook La Nina winter to unfold, having a “double character” over the United States, from colder to the north to warmer over the south.
WINTER 2022/2023 LATEST FORECAST SUMMARY
To simplify al the graphical perspectives, here is what the November update forecast shows for the Winter season 2022/2023:
Europe is expected to have mostly above-average temperatures over most of the continent. Average temperatures are shown over the parts of the west, under the influence of a nearby low-pressure area.
This suggests that there can be periods with more cold fronts and colder days over parts of western and parts of central Europe.
Such a pattern can still permit an breakdown of the flow and a northerly air stream into central Europe later in the year and early next year.
The models are not in 100% agreement over the pattern in the North Atlantic. The main key is the positioning and strength of the pressure systems over Iceland/Greenland relative to the North American pattern.
Precipitation-wise, mostly average-to-drier conditions are forecast over central and western Europe. More precipitation is shown over the southern parts of the continent. The snowfall forecast shows less snowfall over Europe, with potentially more snowfall in the higher elevations.
North America winter forecast looks to be a classical La Nina-type winter. As a result, western and central Canada can expect colder and snowier conditions, along with Alaska and northern United States.
The United States can expect to see a strong north-south pattern development. Over the northern United States we expect to see a colder Winter with more precipitation and snowfall. Colder temperature anomalies are forecast to develop from the northwestern United States into the upper Midwest. Intermittently, colder anomalies can spread into the far northeastern United States.
The Southern United States has a high chance for warmer and mostly drier than normal winter weather. This, however, does not mean that no cold front can reach the southern states. Instead, it shows that in a La Nina pattern, it is much less likely to get frequent cold fronts down to the deep south due to the different jet stream positioning.
Below is NOAA’s official Winter 2022/2023 temperature forecast for the United States. It shows the temperature probability, with an increased cold potential in the northern United States. As seen in the models above, the southwestern part of the country and the east coast have a higher probability of warmer than normal winter weather.
But take note of the trough of “equal” temperatures probability extending down low into the south-central states. That can be interpreted as a potential route of winter cold air outbreaks down from the Midwest.
The official NOAA Temperature outlook points:
- Warmer-than-average temperatures are favored in the Southwestern United States, across the Southeastern states and along the Atlantic coast.
- Below-normal temperatures are favored from the Pacific Northwest eastward to the western Great Lakes.
The official precipitation forecast is also quite similar to the latest model forecasts. We see an equal-to-higher probability for more precipitation (and snowfall) over the northwest, extending into the Great Lakes and the eastern United States. The southern United States is forecast to have a drier-than-normal winter season.
NOAA Official precipitation outlook points:
- Wetter-than-average conditions are most likely in the Pacific Northwest, the northern Rockies, Great Lakes, and Ohio Valley.
- The greatest chances for drier-than-average conditions are forecast in portions of California, the Southwest, the southern Rockies, the southern Plains, the Gulf Coast, and much of the Southeast.
In a La Nina winter, there is usually a problem with the persistence of drought conditions in the south and southwest. Below is the latest drought graphic from NOAA, which shows the current drought conditions in the United States through mid-November.
Strong drought conditions prevail over the south-central and western United States. We can see a gap in the southwest, due to the summer monsoon bringing a decent amount of precipitation.
But the drought conditions in the south are expected to continue and can worsen in a La Nina Winter. The same goes for western parts of the United States, especially southern California.
There is no certainty in the winter forecast at this long lead time. But there is also one very important factor that can change the course of Winter at any time. That is the Stratospheric Polar Vortex.
WINTER STRATOSPHERIC POLAR VORTEX
Winter weather is highly dependent on the Polar Vortex. The Polar Vortex re-emerges every Fall as temperatures drops, and plays a key role in daily to weekly weather development in late Fall, Winter, and even Spring.
The Polar Vortex is a large area of a cyclonic circulation over the entire Northern Hemisphere, from the ground up to the top of the Stratosphere, reaching over 50km/31miles altitude.
Below is our 3-dimensional model of the Polar Vortex, extending from the lower levels upwards into the Stratosphere. The vertical axis is enhanced for better visual purposes. You can see in the image below what the actual structure of the Polar Vortex looks like in mid-Winter, connecting downwards.
In the example above, the Polar Vortex underwent a temporary warming event. These events can disrupt the Polar Vortex, weakening its circulation and changing the weather patterns below.
That is very important for winter weather patterns, as it can change the dynamics and pressure anomalies for several weeks ahead. But even a strong Polar Vortex plays a role in the developing weather patterns.
A strong Polar Vortex usually means strong polar circulation. This tends to locks the colder air into the Polar regions, resulting in mild seasonal conditions for most of the United States and Europe.
But, a weak Polar Vortex can create a disrupted jet stream pattern. This means that it has a harder time containing the cold Arctic air, which now has an easier way of escaping from the polar regions into the United States or Europe.
A Sudden Stratospheric Warming event (SSW) can significantly impact circulation and cause major pressure changes in the Northern Hemisphere. It produces the most stratospheric disruption and eventual weather changes.
One such event occurred in early January 2021. The stratospheric warming wave has spread over the entire North Pole in the Stratosphere, effectively splitting the cold core of the polar vortex into two parts.
One part of the broken polar vortex has moved over North America, and one remained over the European area. At this point, this did not yet influence the winter weather on the surface, as such events begin at over 30km (18 miles) altitude. But the weather influence followed downwards quite soon after.
That is how a stratospheric warming event typically operates. First, it breaks down the upper structure of the Polar Vortex, which then collapses downwards, impacting the weather at the surface.
Below is an image that shows an average temperature pattern 0-30 days after a proper winter stratospheric warming event. High pressure over the Arctic helps to unlock the cold air out of the Arctic regions, sending it down into the mid-latitudes of the United States and Europe.
Looking at snowfall below, we can see above-average snowfall over much of the eastern United States and Europe after a Polar Vortex collapse event. But, again, this is an average response, as the colder air has an easier path towards the south and into these regions after a stratospheric warming event.
Of course, not every stratospheric warming event produces this pattern, but it helps to show us an average image of many events in the past 40 years. A lot depends on the already established weather patterns at the lower levels of the atmosphere and the timing of the stratospheric warming event (early/late winter).
These dynamics can have a large-scale and long-lasting impact on the weather pattern during Winter, so we always closely monitor the stratospheric development.
We will keep you updated on the developing weather trends in the coming seasons, so make sure 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.