The unprecedented El Niño gathering strength in the Pacific Ocean could upend forecasts for UK weather this winter, bringing continuously wet, stormy conditions until spring. El Niño is a natural climate phase that happens when easterly trade winds weaken, allowing the warm water they had piled up in the western Pacific to wash back across the central and eastern Pacific. This swathe of warm water heats the atmosphere and weakens the winds further in a feedback loop.
The phenomenon’s impact on the weather in the UK and north-western Europe is notoriously tricky to predict, because weather patterns in this region are strongly affected by weather phenomena in the North Atlantic. Under an El Niño event of normal intensity, the UK is more likely to experience wetter, windier, stormier weather in the late autumn and early winter, potentially followed by a colder, drier end to winter. 5 graphs that show how the record-breaking El Niño will affect the world However, the sheer size of the current El Niño – already one of the largest on record and still intensifying – could mean that the end of winter and start of spring continue to be wet and stormy, says Adam Scaife at the Met Office, the UK’s national weather service, who leads the agency’s long-range forecasting. El Niños usually increase the likelihood of cold easterly winds prevailing over the UK during late winter.
But a very strong El Niño may reverse that trend, leading to prevailing westerlies late in the season. The weather under those conditions is “still cold, but it’s not extreme”, he says. Scaife first reported this effect of strong El Niños in a 2006 research paper he co-wrote with Thomas Toniazzo, now at NORCE Research in Norway.
The study assessed the weather in the North Atlantic during El Niño years and found that very strong El Niños produced this mild and wet pattern in late winter. The El Niño in 1997-1998, for example, was one of the most powerful on record. It saw high pressure developing in the North Atlantic to the west of the UK over the late winter, leading to westerly prevailing winds that blew milder, wetter, stormier air over the UK and northern Europe.
The same pattern appeared in the 2015-2016 El Niño, when the UK had one of its mildest and wettest winters on record. But it would also offer an opportunity to replenish reservoirs and groundwater after an exceptionally dry summer. Intense fires are already burning in Indonesia, and there could be much worse to come as the Super El Niño ramps up However, Scaife warns it is very difficult to tease apart the effect of a strong El Niño compared with that of a standard-strength one, in part because there are only a few very strong events in the historical record for which we have good data.
El Niños – and their opposite pattern, La Niñas – also vary hugely from year to year and decade to decade, so it can be fiendishly difficult to separate out a signal from the noise in the system. What’s more, it is very difficult to predict weather patterns months in advance, and there is still huge uncertainty over what late winter will hold for the UK. This week, the World Meteorological Organisation (WMO) warned that the El Niño is still intensifying in the tropical Pacific and is set to be the largest on record, fuelling drought, floods and extreme temperatures around the world.
Extract — continue reading at the source.
