Why this year's winter weather is so unpredictable
This year, several factors including the La Niña ocean circulation could affect weather in Britain – here’s what they might mean.
The weather has become abruptly colder in recent days – with snow, frost and the arrival of ‘real’ winter conditions. But is Britain likely to stay chilly through the coming months?
Well, that depends on a few different factors.
Last year saw another warmer-than-average winter, with cold wintry spells in December and January contrasting with wetter, stormy weather later on, according to the Met Office.
Several factors - including the La Niña ocean circulation - could affect weather in Britain this year. Here’s what they might mean.
What could La Niña mean for this winter?
The US National Weather Service has predicted a 57% chance of a La Niña event emerging in the last quarter of this year and persisting through to March.
La Niña is an ocean cycle that can spell a cooler early winter and then a wetter spring for Britain.
El Niño and La Niña are the warm and cool phases of a recurring climate pattern across the tropical Pacific.
The two patterns affect weather and ocean conditions around the world, and broadly speaking have opposite effects on the world’s climate.
During La Niña strong trade winds blow warm water towards the west Pacific causing an upwelling of cool water from the ocean depths in the east Pacific.
This leads to variations in global weather – and the Met Office says it can influence the Atlantic jet stream and our weather here in the UK.
Professor Adam Scaife, head of long range prediction at the Met Office said in 2020, that: “La Niña has a profound effect on weather across the globe with us even seeing impacts that extend across the UK.
“In late autumn and early winter it historically promotes high pressure in the mid-Atlantic, which stops Atlantic weather systems from delivering mild air to the UK, and therefore can allow cold conditions to intensify.
“However, in late winter La Niña can drive a shift of the jet stream towards the poles increasing storminess and heavy rainfall, while bringing milder conditions."
What about the North Atlantic Oscillation?
Another factor that can influence weather in Britain is the North Atlantic Oscillation (NAO) – a large scale atmospheric pressure pattern in the North Atlantic which can affect weather in the UK.
The NAO index is currently positive – meaning there's a large difference in pressure – but is forecast to trend negative in coming weeks.
The Met Office explains: "When the NAO index is well above normal, there is an increased chance that seasonal temperatures will be higher than normal in northern Europe, northern Asia and south-east North America, and lower than normal in north Africa, north-east Canada and southern Greenland.
“The patterns for precipitation (rainfall, snowfall) are more localised, with an increased chance of higher rainfall in northwest Europe and lower rainfall in southern Europe. When the NAO index is well below normal, the tendencies are generally opposite.”
What has the Met Office predicted?
The Met Office's three-month outlook predicts that there is only a 'small chance' of the period from November 2024 to January 2025 being cold.
"Consistent with our warming climate there is only a small chance of the period being cold. However, this does not preclude the possibility of some cold spells and related impacts. These are more likely than normal during the early part of this period," the Met Office said.
"During November, there is a moderate increase in the likelihood of pressure to be higher than average to the north or northwest of the UK, this increasing the likelihood of northerly or easterly winds.
The Met Office forecasts that colder spells will become less likely later in the three-month period.
"Towards the latter part of the period, lower than average pressure becomes more likely to the north with above average pressure across or near to the south of the UK. This favouring westerly winds and a reduced likelihood of cold," according to the forecaster.
It suggests that there may be some cold spells during the period, and says there are standard chances of the period being rainy.
There is a very slightly lower than average chance the period will be windy, the Met Office added.
"Whilst the likelihood of the period being wet is similar to normal, given the time of year, spells of wet weather are still to be expected.
"The wettest conditions are likely over northern and western parts of the UK. Likewise, the likelihood of the period being windy as a whole is similar to normal but some stormy spells remain possible."
How is climate change influencing British winters?
Over the past century, British winters have become 1C warmer, and 15% wetter, according to Carbon Brief.
Six of the 10 warmest winters on record have been in the 21st century, and four of these also rank among the top 10 wettest years.
Extreme cold snaps do still hit the UK, and some winters are colder, according to Carbon Brief – with 2010 being particularly chilly – but the overall trend is towards warmer, wetter weather.
According to Met Office projections, by 2080-2099, the average UK winter will be 2C warmer and 11% wetter than 1981-2000.
The Met Office says: “Observations show a clear warming trend for average UK winter temperature, and this trend is projected to continue in the future due to human induced climate change.
"This doesn’t mean the UK will no longer see cold spells, like we did this year during the first half of January, however cold spells are projected to become less frequent and less severe.”
What about the rest of 2025?
The Met Office has previously said that 2025 has a chance to be the first year with temperatures 1.5C above pre-industrial levels.
The 1.5C threshold is seen as a key point beyond which extreme weather, sea level rises and other negative outcomes are more likely.
The 2015 Paris Agreement aimed to limit global warming to below 1.5C, although this is accepted to refer to long-term trends rather than individual years.
The Met Office’s Dr Nick Dunstone, who led the forecast, said in 2023 that the forecaster expected a further 'record breaking' year for temperature.
He said, "For the first time, we are forecasting a reasonable chance of a year temporarily exceeding 1.5C.”
“It’s important to recognise that a temporary exceedance of 1.5C won’t mean a breach of the Paris Agreement. But the first year above 1.5C would certainly be a milestone in climate history.”
