.png?width=1200&auto=webp&quality=75 "What is Sudden Stratospheric Warming – and how could it impact London’s winter weather?")
Something unusual is happening high above the Arctic, threatening to bring cold weather, frost, and strong blasts of icy wind to London and the UK.
The weather event – known as Sudden Stratospheric Warming – could take place as soon as next week, with forecasters at the Met Office warning of a 70% chance of colder weather and frosty spells.
If confirmed, the weather event would be the earliest major one of its kind ever recorded in the satellite observation era.
Sudden Stratospheric Warming happens when the Polar Vortex collapses, but is also closely linked to El Niño – which has continued to strengthen to unprecedented levels across the Pacific.
The chain of events already looks to be happening just 10 km to 50 km above the Earth’s surface, though the phenomenon is not yet guaranteed.
In 2018, the breakdown of the Polar Vortex caused by Sudden Stratospheric Warming wreaked havoc, bringing the “Beast from the East” to the UK, forcing schools to close and widespread transport shutdowns.
Now, it could happen again.
What will Sudden Stratospheric Warming mean for London?
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The stratosphere could begin to warm from November 5
NetWeather/PA Archive
What is Sudden Stratospheric Warming?
Sudden Stratospheric Warming happens when the Polar Vortex is disturbed or deformed.
The Polar Vortex is a strong current of air, spinning in an anti-clockwise ring around the Arctic at around 150mph and trapping the coldest air around the North Pole.
But in what has been described by BBC Weather as a “spinning top”, the spin cycle can wobble or break up, sometimes even turning in the opposite direction.
The difference between a stable and unstable Polar Vortex
NOAA
When this happens, cold air sinks into the troposphere – the layer below the stratosphere – and changes the shape of the jet stream below it.
The jet stream is a ribbon of fast moving air which determines most weather conditions in the UK and when it wiggles and winds, it creates “Rossby Waves”.
While this is taking place, the stratosphere is getting warmer rapidly, sometimes even by up to 50C in a couple of days – hence the name, Sudden Stratospheric Warming.
Why it could mean colder weather for London
When the jet stream oscillates, blocking areas of high pressure can form over the North Atlantic and send bitterly cold Arctic air towards northern Europe.
The jet stream oscillates and threatens to disrupt the Polar Vortex
Met Office
This in turn leads to colder, frostier, and drier weather in the UK and northern Europe.
Colder weather in the UK is not guaranteed, but if confirmed, it does increase the chances of a frostier and wintry season by as much as 70%, according to the Met Office.
This chain of events usually takes place later in the season, so forecasters will be tuned in to see how much cold weather the UK could see if all the conditions line up.
What does Sudden Stratospheric Warming have to do with El Niño ?
El Niño has already broken records to become the strongest weather event in history and is closely related to the weather phenomenon that could be taking place next week.
The weather phenomenon risks disrupting the Polar Vortex, triggering Sudden Stratospheric Warming.
El Niño heat map recorded last month shows a strong to severe presence with temperatures above average
European Centre for Medium-Range Weather Forecasts
An El Niño phenomenon is declared when sea surface temperatures are higher than usual over a period of several months.
As a result, warm seas slosh back into the central Pacific, triggering thunderstorms and warming the atmosphere in the region.
As the warm air expands, it increases the pressure in the troposphere, which has the potential to disturb and displace the Polar Vortex in the stratosphere above it.
Sudden Stratospheric Warming has not yet been declared.
The long-range forecast for next week predicts highs of just 12C and lows of between 6C and 7C. Conditions are likely to be dry, with gentle breezes and gusts of around 29mph.
But it can take anywhere between two to six weeks for the effects of Sudden Stratospheric Warming to be felt.
“A highly unusual disruption of the stratospheric polar vortex is now underway,” the Met Office told The Independent. “If it becomes a major Sudden Stratospheric Warming (SSW), it will be the earliest such event on record,” it added.
“The current large El Niño may be contributing to the disturbance, as El Niño is known to increase the likelihood of SSWs. While SSWs often promote the chances of cold UK weather, at this stage there remains uncertainty over the influence, if any, on weather at the surface,” The Met Office said
What was the Beast from the East?
The Beast from the East was the historic cold wave that hit the UK in late February of 2018.
Cold and dry air plunged into northern Europe, while cold snaps collided with Storm Emma, triggering blizzards and freezing rain across the UK.
London was hit by a blast of wintery weather dubbed Beast from the East in 2018
AFP via Getty Images
The Beast from the East froze over canals in London
Sean Martin
The snowstorm was largely triggered by Sudden Stratospheric Warming and saw thousands of schools close and transport networks grind to a halt.
A 60-year-old man from Welling in London died after trying to save his dog from a lake during the weather phenomenon.
As many as 11 others died amid the snowy and wintry conditions, either from accidents caused by the weather or from freezing to death.
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