New Winter 2024/2025 snowfall predictions are in, and they show a global weather signal from a weak La Niña in the Pacific. Compared to the forecast from last month, the new data has increased the amount of snowfall over the northern half of the United States and southern Canada but shows less snowfall over Europe.
First, we will quickly look at the leading global weather driver for the upcoming weather seasons, the cold La Niña, and what is its expected influence on the Winter 2024/2025 season.
We will examine the snowfall predictions month-by-month for the United States, Canada, and Europe, using the two leading global long-range forecasting systems. The latest forecasts now also include the data for February, so the whole winter is covered in the forecast.
SEASONAL WEATHER DEVELOPMENT
ENSO is a region of the equatorial Pacific Ocean that changes between warm and cold phases. Typically there is a phase change around every 1-3 years. The warm phase is called El Niño, and the cold phase is called La Niña.
ENSO phases significantly influence tropical rainfall, pressure patterns, and the complex dynamics between the ocean and the atmosphere. The image below shows the circulation pattern of a cold phase, which is forecast to be active over the upcoming Winter season.
Changing the circulation, ENSO significantly impacts tropical rainfall and pressure patterns, altering the atmosphere-ocean feedback system. This feedback system spreads the ENSO influence globally, especially the Winter temperature and snowfall patterns.
Below is the latest September ocean anomaly analysis. It shows colder-than-normal ocean surface in the central and eastern ENSO regions. These cold anomalies have a “wave-like” shape. This is because of the strong easterly trade winds that push the waters towards the west, bringing deeper, colder water to the surface.
Below is an official IRI probability forecast image, with the long-range forecast of the central ENSO region. As forecasted, La Niña conditions will last over the Fall and Winter. A weakening of the La Niña is expected early next year, with a shift to a neutral phase by summer 2025.
To better understand the ocean surface changes, we produced a high-resolution video animation that shows how the ocean temperatures went from warm to cold anomalies across the ENSO regions in the tropical Pacific.
Changes in the oceans are well known to also change winter weather patterns and, thus, the snowfall potential. We will take a closer look at the weather influence that La Niña usually shows over North America, as it has a more direct impact.
Europe is not known to have any specific/direct influences, as it is too far from the source. But that does not mean it has no impact.
La Niña does change the weather globally, but apart from the direct influence over the United States and Canada, places like Europe have many other factors at work before any La Niña influence can spread this far.
NORTH AMERICA WINTER PATTERNS
The main influence of these ocean anomalies can be seen in the changing jet stream patterns. A jet stream is a large and powerful stream of air (wind) at around 8-11km (5-7 mi) altitude, flowing like an atmospheric river.
Historically, a strong blocking high-pressure system in the North Pacific is the most typical effect of a cold ENSO phase (La Niña). That usually redirects the polar jet stream down over the northern United States.
The circulation of the strong high-pressure system promotes the development of a low-pressure region over Alaska and western Canada. It pushes the jet stream downwards between the two strong pressure systems and is marked above by the blue lines.
The image below shows jet stream redirection from La Niña and the resulting weather patterns developing over the United States and Canada.
The displaced jet stream brings colder temperatures and winter storms from the polar regions down into the northern and northwestern United States. Warmer and drier winter weather prevails over the southern states.
Looking at the temperature analysis for some of the more recent La Niña winters, we can see the cold anomaly area under the jet stream in western Canada and the northwestern United States. A cooler area extends over the Midwest and down into the south-central plains.
Warmer-than-normal weather and mild winter conditions develop in the southwestern and eastern United States and eastern Canada. The main winter weather dynamics are usually between the warm and cold anomalies in the Midwest and the central United States.
Data also shows that the La Niña jet stream pattern significantly affects the snowfall potential over North America as the pressure systems take a different path.
The colder air is more easily accessible to the northern United States, which increases the snowfall potential if moisture is available. In the graphic below by NOAA-Climate, you can see the average snowfall pattern for weak La Niña years, just as expected for this Winter season.
In addition to the northwestern United States and the Midwest, the northeastern United States and eastern Canada show more snowfall potential in such ENSO conditions.
It’s time for some actual Winter snowfall predictions from the latest forecast models issued in mid-late September. This latest round of data now also includes the month of February, so we will have the first full snowfall forecast for the whole winter.
WINTER SNOWFALL PREDICTIONS – FIRST UPDATE
The format of this snowfall forecast is simple. We look at two well-established seasonal weather forecasting systems, the ECMWF and the UKMO. The data used to produce these images is the latest available, from mid and late September.
You will first see the seasonal average snowfall forecast for December-January-February, and then we will do a monthly breakdown. There are a lot of details in the monthly forecast that the whole seasonal average cannot show.
These forecasts show the snowfall anomaly. This means it shows the areas forecast to receive more (or less) snowfall than normal. For example, if an area is forecast to receive less snowfall than normal, it doesn’t mean it will receive no snow. It just means less snowfall than usual is expected.
ECMWF WINTER 2024/2025 SNOWFALL FORECAST
We will start with the ECMWF, the most often used and highly regarded seasonal forecasting system. We will first look at the Europe forecast, followed by the United States and Canada.
First, the seasonal average shows below-average snowfall over most of the continent. However, more snowfall than normal is forecast over Scandinavia due to the influence of a low-pressure system and the jet stream over northern Europe.
The December snowfall forecast shows less snowfall than normal over much of the continent. A small area of normal snowfall is indicated over the Alps, with more snow again over northern Scandinavia.
The January forecast shows reduced snowfall potential over much of the continent. Overall the forecast is very similar to the previous month, with perhaps even less snowfall over the Alps.
February shows no major improvement, with most of the continent still under much less snowfall than normal, except for the northern parts under the jet stream. Some small snowfall areas are indicated over the Alps, similar to December.
NORTH AMERICA ECMWF SNOWFALL FORECAST
The seasonal average for North America shows that most of the central and southern half of the United States is forecast with below-average snowfall. But compared to the forecast from last month, there is more snowfall in the forecast for parts of the northern United States and the upper Midwest.
Canada shows much more snowfall over a large part of the country, except for the far southeastern area.
The December snowfall forecast shows less snowfall over almost the entire United States and more snowfall only over parts of the north-central United States. Surprisingly, some snowfall areas are also indicated over the southeast. Canada shows the usual above-normal snow, except over the south and southeast.
January snowfall forecast shows an expansion of snowfall area starting. A strong area of above-normal snowfall is forecast over the northwestern United States and the upper Midwest. More snowfall is also seen expanding into the southeastern parts of Canada.
This January snowfall forecast from ECMWF still shows less snowfall across the central, eastern, and southern United States. Overall, the January forecast looks similar to a more typical La Niña pattern, except for the Northeastern United States, which should usually get more snowfall in such a pattern.
The first look at the February snowfall forecast shows a further expansion of the snowfall area, now covering much of the northern United States, expanding deeper over the Midwest and also into the northeastern United States.
An interesting area of below-normal snowfall is forecast over far eastern Canada, with less snowfall still forecast over the southern half of the United States. But overall, this looks much closer to the expected La Niña snowfall pattern in past winters.
UKMO WINTER 2024/2025 SNOWFALL FORECAST UPDATE
We use the UKMO long-range forecasting system along the ECMWF to estimate how “dependable” each forecast is. If both forecasts show a very similar image, it gives a higher confidence in its accuracy.
First, looking at the seasonal average for Europe, we can see another very weak snowfall forecast identical to the ECMWF. Most of the continent is forecast to have less snowfall than normal, except for some northern parts under the jet stream.
The December snowfall forecast shows less snowfall over Europe, with an interesting area of increased snowfall over the sub-Alpine region.
No major change is forecast for January across the continent. As the forecast shows, snowfall potential is further decreased, with more snowfall over the far north again, following the jet stream.
February shows even less snowfall over the continent, with stronger negative values. This is a very weak snowfall outlook, but it is already far into the forecast, so it has a reduced predictability.
Overall, both models agree on a weak snowfall season over Europe, except for the far northern areas and some central parts around the Alps.
NORTH AMERICA UKMO SNOWFALL FORECAST
The average seasonal forecast for North America shows more snowfall potential across the northwestern United States and southern Canada. Less snowfall is forecast over much of the southern and eastern United States and over far southeastern Canada, just like in the previous model.
The December snowfall forecast shows more snowfall over much of Canada and parts of the far northern United States. Less snowfall is forecast over the rest of the United States, and far southeastern Canada.
January snowfall forecast starts to increase the snowfall cover over southern Canada and into the northern United States. More snowfall is starting to expand into the upper Midwest, and also into the northeastern United States.
The first February snowfall forecast shows a continuation of the snowfall area from January, covering much of the northern United States and upper Midwest and keeping the snowfall potential over the far northeastern United States.
Less snowfall than normal is forecast over the southern half of the United States, typical for a La Niña winter.
Overall, this is a slightly different forecast from the ECMWF, having more snowfall over the northern United States and the Midwest.
WINTER 2024/2025 OFFICIAL OUTLOOK
We can also find hits for the snowfall season in the official Winter 2024/2025 outlook by NOAA.
Below is the temperature forecast for the United States, issued in September. It shows the probability of winter temperatures, with colder chances in the northern United States. The southwestern part of the country and the east coast have a higher probability of warmer-than-normal weather.
Just like the snowfall forecasts above, this also shows colder air over the northern and northwestern United States. There is an area of “equal chance” expanding into the Midwest and parts of the eastern United States, which could indicate the potential “highway” for some of the cold air movements from the northwest.
The official precipitation forecast also shows a classical La Niña pattern. We see an equal-to-high probability of more precipitation over the northern half of the United States. Combined with some colder air anomalies, this shows the main snowfall potential over the northwestern United States, the upper Midwest, and parts of the Northeast.
The southern United States is forecast to have a drier-than-normal winter season. In a typical La Niña winter, there is usually a development and persistence of drought conditions in the south and southwest of the United States.
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