The first forecast trends for Summer 2024 are here, and they show a dynamic summer pattern in the atmosphere. Most of it has to do with the El Niño now starting to disappear, with a new La Niña cycle now forecast to emerge during Summer, and already showing a visible signal in the summer forecast.
When trying to understand any weather season and long-range forecasts, we must realize that many global factors can influence weather patterns.
Over the Northern Hemisphere, the upcoming months will be a transition period between the El Niño and the La Niña, both in the Oceans and in the Atmosphere. And the Summer season will be right in the middle of this process.
EL NINO SEASONS END
One of the main drivers behind the Winter weather patterns and early spring was the El Niño. This is a warm phase of an oceanic oscillation called ENSO. It is found in the equatorial Pacific and alternates between warm and cold phases.
The warm phase of ENSO is called an El Niño, and the cold phase is called a La Niña. Each phase has its specific influence on the pressure patterns and the resulting weather. Below is the ocean temperature analysis for the October to January period. You can see the belt of warm ocean anomalies across the Pacific. That is the El Niño anomaly.
Looking at the past data, we can compare the El Niño data with the pressure anomalies, and we get an image of what a typical El Niño Fall/Winter period looks like. You can see a belt of low-pressure anomalies extending from the North Pacific, across the southern United States, into the Atlantic and northern Europe.
A high-pressure anomaly is typically seen over Canada, and a ridge expands into Europe.
Below is the actual pressure anomaly pattern for the November-February 2024 period. It shows a very similar pattern to the average El Niño image above: a belt of low-pressure systems from the North Pacific, across the southern United States, into the Atlantic and northern Europe.
You can also see the high-pressure anomaly over Canada and a strong high-pressure area pushing into southern and central Europe. This is a very typical El Niño winter pattern overall. It also shows the very important impact that these ocean anomalies have on the seasonal weather patterns and our daily weather.
But looking at the latest ocean anomalies across the ENSO regions, you can see that the strong, warm waters are almost gone. You can even see some cold patches starting to appear. This signals the end of El Niño and the eventual rise of the cold La Niña anomaly.
A strong subsurface cold pool is the main pre-condition for an El Niño breakdown. With the aid of the trade winds and ocean currents, these subsurface anomalies move from west to east, eventually coming to the surface over the eastern Pacific.
The video below, produced from NOAA subsurface data, explains this process. It shows the ocean temperature anomalies for the past two months and shows a rapid breakdown of the warm pool below the surface.
In January, we saw a strong expansion of the cold pool towards the east. It has begun to erode the warm anomalies and is now starting to appear at the surface, as patches of colder than normal waters.
Below is a CPC analysis/forecast graphic that shows the long-range outlook for the main ENSO region. You can see the seasonal probability of the ENSO phases, clearly showing the current warm phase breakdown and the emergence of a very likely cold phase in late summer 2024 and lasting into 2025.
Looking at the long-range ocean anomaly from the NMME forecast, you can see an area of cold ocean anomalies expanding across the entire tropical Pacific by early Fall 2024. An event of this magnitude is strong enough to have a profound atmospheric response during the Winter of 2024/2025.
Based on all this forecast data, we know that El Niño is quickly on its way out. But, such large-scale events tend to work on longer time scales. This means that despite a rapid breakdown of the warm ocean anomalies, the atmosphere can take some time to adjust and respond to that.
This means that the 2024 summer will be a transition period from one ENSO phase to another, likely creating some unusual anomalies in the process.
THE LA NINA SUMMER
To understand what such a shift means for the atmosphere, we have produced an image that shows surface pressure during past La Niña summers. You can see that a high-pressure surface anomaly is the usual La Niña signature during summer seasons.
Looking at the actual surface pressure anomaly forecast, we can see every similar pattern over the tropical Pacific. High pressure is emerging in the eastern Pacific tropics, indicating an emerging La Niña. This means that during summer, at least the tropical atmosphere is already adjusting to the new La Niña cycle.
However, this summer will not have a “full” La Niña but rather a starting one. And that can mean a difference from past La Niña summers. It is just something to consider as we look at the pressure patterns and temperature.
Below, we have the 500mb geopotential height for a typical La Niña summer. It shows a tendency of high-pressure anomalies in the pattern over the United States. A trough is over the northwestern United States, while a broad low-pressure area extends from eastern Canda over to northern Europe.
The temperature anomaly for a typical La Niña summer shows above-normal temperatures over much of the United States and Canada. But over Europe, we can actually see a trend for lower temperatures than normal, but the signal strength is very weak.
We kinda know what to expect, but we do have to consider that this summer, we will be on a rapid shift from one ocean anomaly to the next. So moderately different pattern can be expected than the usual one.
Now, it’s time to look at the early weather trends for Summer 2024 across Europe, Canada, and the United States and see how this transition might affect the atmosphere.
SUMMER 2024 FIRST LOOK FORECAST
We will examine the early trends from the two most used seasonal forecasting systems: the ECMWF from Europe and the CFSv2 from NOAA in the United States. We like using two very different forecasting systems, which helps us see more potential scenarios and see how well the models agree on a certain trend.
ECMWF is statistically a better long-range model, so we usually start with its forecasts.
Generally, the ECMWF model is at the top as far as “reliability” goes. But no long-range/seasonal forecasting system can be called “reliable“. This is because we only look at trends and how the weather patterns are evolving on a large scale and over longer periods.
The forecast period we will focus on in all models is June-July-August (JJA 2024). This period covers the meteorological Summer and is the peak of the warm season.
Going over Europe first, we can see the pressure pattern forecast from ECMWF below. It shows a low-pressure area over northern Europe and a high-pressure system over the southwest. This helps to bring warmer-than-normal temperatures up from the south into the central and western parts.
A low-pressure area over northern Europe is something that was indicated in the past La Niña summers. So this is one indication that the La Niña influence will be spreading rapidly across the globe during summer.
Looking closer at the temperature pattern over Europe, we see the warmer-than-normal weather over a large part of the continent. But, the exception is found towards the north, which is under the influence of a low-pressure area and shows normal summer temperatures.
This is not a lower-temperature signal that was seen in the images for past La Niña summers. But it does not show a very scorching summer for now.
Going to precipitation, we can see mostly drier conditions forecast over central and southern Europe under the high-pressure zone. However, wetter conditions are forecast over the northern parts, again due to the lower pressure and more unstable weather.
Overall, there is an indication of La Niña’s influence over Europe, which is usually hard to track, even during winter. But there are some visible patterns that are similar to he expected pressure anomalies for a La Niña summer.
UNITED STATES AND CANADA SUMMER 2024 FORECAST
The pressure pattern forecast for North America shows a low-pressure area over northeastern Canada and parts of Greenland, also likely to extend into central Canada. Over the United States, a ridge rises from the south upwards into the Midwest and the Northeast.
There is a slight trough indication over the western United States, which could mean a gap and a reduction of strong warm anomalies. This is again a similar pattern to the one we saw as the usual La Niña summer anomaly.
So, while each summer so far has been hot in most places, we can use these anomalies to find which places are likely to have more/less heat waves and prolonged events with above-normal temperatures.
Looking at the temperature forecast, we can see mostly warm anomalies over the southern United States, expanding into the plains and up toward the Great Lakes. No stronger warm anomalies are found over the western United States as expected, and also across a large part of the eastern United States.
This shows a high tendency for prolonged heat events over the southern United States, with the waves expanding across the plains to the north and towards the upper Midwest.
Canada is also seen warmer than normal across much of the country apart from the north, which is under the impact of the low-pressure area. The strongest anomalies are, as mentioned, around the Great Lakes and in far western Canada.
The precipitation forecast over North America also shows less rainfall over the southern and western parts of the United States and parts of western Canada. More rainfall is expected across the Midwest and the Pacific Northwest.
We also saw a temperature anomaly over the Midwest, so this is an interesting signal. But if we know how the pressure pattern looks, we know that the Midwest will be under a more southerly to southwesterly flow. That brings heat but also moisture, which is supportive of thunderstorm formation.
So when we have an overlap of increased rainfall and increased temperatures, like over the Midwest, it can be seen as an increased thunderstorm activity.
However, we are looking at the early summer trends, so the precipitation picture will become more defined with new runs. But overall, the summer weather pattern over North America does look to have a visible La Niña signature in the weather patterns.
It makes sense, as North America is much closer to the source region in the Pacific, so it is expected to feel the early changes of the new La Niña emerging.
CFS SUMMER 2024 EARLY FORECAST
In contrast to the European model, we like to use the main North American long-range model, the CFS version 2 from the NOAA/NCEP in the United States.
The CFS model differs from the ECMWF, with a high-pressure system over Canada and Northern Europe. Overall, this is a slightly different forecast than the ECMWF. Based on the distribution of potential low-pressure areas, it also looks like the CFS wants to prolong the influence of the El Niño.
Looking at Europe first, the forecast shows warmer-than-normal temperatures over most of the continent. This is a combination of a strong high-pressure system sitting over the continent and the trend of an increasing number of summer heat waves.
The North American temperature forecast below shows a somewhat similar picture to the ECMWF. The CFS shows that the summer will be warmer than normal over the Midwest, Northeastern, and Southern United States, with a gap in warm anomalies across the central United States toward the Southeast.
The Western United States does not show any major warm anomaly and is indicated as a rather “normal” summer. A strong warm anomaly is forecast over Canada, with the direct influence of the high-pressure systems forecast in that area.
Looking at precipitation, we can see Europe separated into two main areas. Wetter Summer conditions across the western and southern parts of the continent, and drier over the central parts and towards the east.
The CFS forecast for North America shows less precipitation over far eastern Canada, the west coast of Alaska, the southern United States, and the central plains. Wetter conditions are forecast over much of the northern and eastern United States and southern and western Canada.
The potential for drought conditions is higher than usual over the southern United States and parts of the central plains.
SUMMER 2024 OFFICIAL EARLY OUTLOOK FORECAST
The NOAA official Summer temperature outlook shows that most of the United States is expected to be warmer than normal, apart from the northern Plains. The core warm anomalies are so far focused on the western parts of the United States and the far east.
This is unlike both models above, but this is a first-look forecast, so it’s normal to see some difference between various forecasts. That is especially true when comparing these human-made outlooks to computer model products like the ECMWF and CFS above.
The official Summer precipitation outlook is closer to the model forecast. We see an equal-to-higher probability for more precipitation over the eastern United States. The models were focused more on the north and northeast, but there is agreement over the northeast.
Both models also had a slight tendency for drier conditions over the western and southern United States, so this is also a similar idea. But, there is less agreement over the northwestern United States, where less precipitation is only shown in the official outlook but not in the models.
We will release regular updates as fresh forecasts and data are available. 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.
SEE ALSO:
An early La Niña watch has been issued by NOAA, as the shift into a Cold ENSO phase is now forecast, impacting the 2024/2025 Weather patterns
