What is La Niña and how could it change Europe’s weather?

The long-awaited La Niña has finally arrived but it is weak and meteorologists say it’s unlikely to cause as many weather problems as usual.

Experts have been expecting the arrival of the climate phenomenon since last spring but finally, the cooling of waters in the central equatorial Pacific Ocean was confirmed in early January by the National Oceanic Atmospheric Administration (NOAA). Its counterpart, El Niño ended in June last year after an unusual three-year stretch.

Lars Lowinski, a meteorologist at Weather & Radar, says forecasts for the winter season 2024/25 suggested a much more pronounced event starting in summer.

“In reality though, it took many more months, with a clear signal only emerging in December 2024, and it is fairly weak compared to what we saw between late 2020 and 2023,” he says.

Its late appearance is likely to be the subject of much research. Experts at the NOAA are already wondering if La Niña’s delayed arrival may have been influenced or even masked by the world’s warming oceans.

What is La Niña?

The El Niño Southern Oscillation (ENSO) is an alternating pattern of sea surface temperature and atmospheric changes in the tropical Pacific Ocean. Last year it brought drought, food shortages and deadly heat in some parts of the world.

La Niña is one phase of this cycle, characterised by cooler-than-average sea surface temperatures in the east-central Equatorial Pacific. The opposite end of this sea surface temperature swing, El Niño, features warmer-than-average surface water.

ENSO is a seasonal phenomenon meaning it lasts for several months in a row, bringing atmospheric changes which impact weather patterns around the world.

It can change global temperatures as well as rain or snow patterns in usually relatively predictable ways. La Niña tends to decrease global temperatures, bringing drier weather in the South and West of the Americas. In Indonesia, northern Australia and Southern Africa, it brings wetter weather.

It typically also brings more Atlantic hurricanes but meteorologists are forecasting that this phase will dissipate by summer when the worst of the season begins.

What does La Niña mean for Europe’s weather?

Lowinski says the biggest signal of La Niña in Europe can be found during winter. This is because of something called a teleconnection mechanism – large-scale weather patterns in other parts of the world that interact with those closer to home.

Two different areas in the Pacific are being monitored: the Central Pacific (CP) and the Eastern Pacific (EP). It is important to differentiate between the two because what is happening in these two basins has different impacts on our weather.

“If the strongest cold anomaly during La Niña is in the EP region, the North Atlantic and western European region tends to weaker storms or low-pressure systems and more blocking highs which often leads to drier and sometimes colder conditions,” he says.

“However, a cold anomaly in the CP region tends to result in a pattern that resembles a so-called positive North Atlantic Oscillation (NAO) pattern, with a stronger jet stream and more storm activity across the near Atlantic and western Europe, resulting in milder, wetter and windier conditions.”

That’s what happens in theory, Lowinski clarifies, but other major players can affect our European weather like the NAO, winds in the stratosphere near the equator and even tropical convection over the Indian Ocean.

On top of this, current forecasts suggest a return to neutral conditions before summer 2025, so there likely won’t be any strong tendencies either way this time.