Climate forecasters say there is a good chance the world could see a long-lasting weather system begin next month, potentially bringing storms and even snow to the UK until March 2025. The National Oceanic and Atmospheric Administration’s Climate Prediction Centre in the US, says there is a 60% chance that a weak La Niña event will develop in November.
La Niña is part of a natural climate cycle that can cause extreme weather across the planet. During La Niña winters, the UK often experiences a colder and stormier winter with higher chances of snow, especially in northern and central areas.
La Niña is the cool phase of the El Niño-Southern Oscillation – a naturally occurring global climate pattern that involves changes in wind and ocean temperatures in the Pacific Ocean. During La Niña, the trade winds intensify and cold water from the depths of the sea rise up, resulting in cooler than average ocean temperatures in the eastern Pacific.
These cold ocean temperatures and changes in the atmosphere affect the position of the jet stream — a narrow band of fast moving air flowing from west to east around the planet — by bumping it northward. The jet stream sits over the ocean and can tap into its moisture, influence the path storms take and boost precipitation.
Michelle L’Heurex, a climate scientist at the NOAA, explained that La Niñas tend to last longer and be more recurrent than El Niño events. “We had three back to back winters where we had La Niña conditions, which was unusual because the only other case of that happening was back in 1973 to 1976.”
Climate scientist at the NASA Goddard Institute for Space Studies Ben Cook said the forecast for this autumn is “unusual although it’s not unprecedented”. He aded that frequency of La Niña events can be stressful for regions that have been dealing with drought lately, such as East Africa. “If we’re moving into another La Niña event, it means kind of a continuation of those really bad conditions.”
A Met Office spokesman said: “The conditions for declaring ‘La Niña’ differ between different agencies, but during an event sea temperatures can often fall 3-5 °C below average. Cooler, drier than average weather is experienced in the tropical eastern Pacific.
“There are also neutral phases of the cycle when conditions are closer to the long-term average (within +/- 0.5 °C). These may be within a period of warming or cooling in the cycle. Approximately half of all years are described as neutral.”