An El Niño is now “firmly established” and set to intensify even further in the run up to December.
The phenomenon, which is declared when sea temperatures in the tropical eastern Pacific rise 0.5°C above the long-term average, is set to have major impacts globally on rainfall and temperature patterns, resulting in more flooding, drought and extreme heat.
In the UK, the Met Office said it’s expected we’ll experience wetter, stormier conditions throughout autumn. This could mean flooding and strong winds are more likely which can, in turn, impact people’s homes, businesses and disrupt travel.
Some experts have also predicted a colder, drier winter as a result of the brewing “super” El Niño.
But given El Niño is raising sea surface temperatures, and our autumn has been particularly mild; how would it make things colder?
In a piece for The Conversation, she explained how weather systems across the globe can influence each other through links called “teleconnections”.
“Through these teleconnections, El Niño is linked to the North Atlantic oscillation, a weather pattern which involves differences in air pressure over the ocean,” she said.
“El Niño is associated with the oscillation’s negative phase, when this pressure difference is less than usual.”
This can “weaken the winds” that carry mild air from the Atlantic to the UK, said the expert, increasing the chance of cold but calm weather later on in the winter.
El Niño can weaken it, which can, in turn, “disrupt” the jet stream which has an impact on our weather.
Wait, what’s the jet stream?
The Met Office explained the jet stream “flows high overhead” and causes changes in the wind and pressure at that level.
When there’s lower pressure within the system, it can bring strong winds and stormy weather, whereas higher pressure typically results in lighter winds and dry skies.
So, by weakening the vortex, and disrupting the jet stream, the UK weather shifts.
It’s been suggested that the arctic (north) polar vortex is showing stronger signs than usual for this time of year. In theory, this is a good thing as it helps to keep very cold winds and conditions around the North Pole.
But when it’s knocked off kilter, which El Niño has the potential to do, it can cause extremely cold air to escape and bring wintery conditions further south.
This is likely to come after El Niño’s peak in December, as The Met Office explained: “Later in winter, following the peak of El Niño, the stratospheric polar vortex can become weaker. This may raise the chance of Sudden Stratospheric Warming events, which can increase the potential for cold weather.”
They added that while autumn’s weather will be “changeable”, looking ahead, “dramatic nationwide snow and prolonged freezing conditions are not the central themes of the current forecast”. But you’ll probably want to be layering up come mid-winter.
