It is usually the time for harvests and falling leaves. But autumn this year could bring snow and freezing frost, weathermen are warning.
The Met Office says that a disturbance in the cold winds swirling high above the Arctic could bring wintry conditions in just weeks.
The polar vortex develops every autumn, and helps keep freezing air trapped around the North Pole.
However, forecasts predict a dramatic weakening of the polar vortex, with some even indicating the winds could reverse direction by mid–November.
If this happens, the jet stream will be allowed to wander from its usual position, increasing the risk of cold air moving southwards out of the Arctic.
It could also cause a ‘blocked weather pattern’ that encourages high pressure to become established over the UK, bringing cold, dry air.
Speaking to the Daily Mail, Dr Regan Mudhar, a weather scientist from the Université de Lausanne, said we ‘certainly can’t rule out’ the possibility of snowfall.
A swirling vortex of winds known as the polar vortex (illustrated) has unexpectedly weakened and now threatens to bring icy weather to Britain
The polar vortex sits in a high region of the atmosphere called the stratosphere, about four to 31 miles (10–50km) above the Earth’s surface.
While it is well above the weather we typically experience on a day–to–day basis, it can still have a big impact on weather patterns in the Northern Hemisphere.
During the winter, the polar vortex is not stable and can shift position, stretch, weaken, and even split apart.
The typical source of disruption is something called sudden stratospheric warming (SSW).
This happens approximately every other winter when disturbances in the stratosphere cause air temperatures to rise sharply over just a few days.
However, these SSW events typically don’t occur until much later in the winter.
Dr Mudhar explained: ‘The stratospheric polar vortex is usually pretty strong and stable in the winter time, which means it generally only breaks down around every other winter anyway.
‘But in early November, it is also still on its way to reaching its peak strength, and break downs at this time of year are very uncommon.’
Dr Mudhar points out that the last time the polar vortex broke down in November was in 1968, and even that occurred late in the month.
When the polar vortex weakens, it shifts the position of the jet stream, making it more likely that freezing air from the Arctic will escape to lower latitudes
Scientists currently aren’t sure why the polar vortex is showing signs of weakening so early in the season.
El Niño events are known to cause disruption to the polar vortex by triggering shockwaves of pressure called planetary waves, but these don’t normally start to take effect until January or February.
Scientists are actively investigating the event using a large number of models and simulations to see if they can reach a better understanding of the cause.
These kinds of vortex disruptions typically bring outbreaks of cold weather to North America, Asia and Europe.
The Met Office’s latest long–term forecasts suggest that the UK is already likely to see a stormy start to winter, followed by a colder spell towards the end of the season.
But this sudden disruption to the polar vortex could mean wintry weather arrives somewhat earlier than expected.
Dr Mudhar said: ‘If it’s already cold and wet, then combining with the cold Arctic air that has now been able to spill towards the UK could lead to snow.
‘But we are really in quite uncharted territory with this as the earliest vortex breakdown on record, so it is very difficult to predict this far out.’
Experts say that this could bring snowfall to the UK, like the infamous ‘beast from the east’ in 2018 (pictured), but this isn’t likely until later in winterÂ
On the other hand, some experts suggest that the extremely early disruption to the polar vortex may actually rule out the possibility of snow.
Later in the winter, a disruption to the polar vortex could bring very cold air over the UK.
However, the air over the North Pole currently hasn’t had enough time to cool, which could mean the effects on Britain’s weather are limited.
Dr Simon Lee, lecturer in atmospheric sciences at the University of St Andrews, told the Daily Mail: ‘The jet stream usually shifts further south towards Spain and Portugal, taking with it the usual flow of mild and wet westerly winds that often dominate winters in the UK.
‘This can mean an increased risk of snow in parts of the UK on average. However, it is still early in the winter, and the coldest Arctic air masses have not yet become fully established.’
Professor Andrew Charlton–Perez, of the University of Reading, told the Daily Mail that it is ‘unlikely’ for the UK to see snow given how early in the season it is.
It will only be later in the season that a stronger link between an SSW event and snowy conditions in the UK becomes established.
But that doesn’t mean the polar vortex won’t cause problems for the UK.
Professor Charlton–Perez says: ‘What will be more important is if it leads to a period of dry weather given the poor state of our water resources after an exceptionally dry and warm summer.
‘I think we need to be more concerned that this could prevent the recharge of our reservoirs over the winter.’
