The polar vortex just set a new record but experts aren't sure what it means for this winter's weather

The spiralling winds of the polar vortex high above the Arctic have reversed direction marking the earliest 'major sudden stratospheric warming' on record.

These polar winds usually blow in a westerly direction keeping cold air locked high above the North Pole.

However in recent weeks the polar vortex has weakened and shifted position. Observations have now shown a switch to easterly winds, which experts say defines a 'major sudden stratospheric warming' or SSW.

Similar disruptions can occur during winter and are often linked with colder weather in the UK. But this event happening so early in autumn is unprecedented in modern observations.

The polar vortex is a normal feature of our climate in the months around winter. As the North Pole tilts away from the sun, temperatures above the Arctic drop and strong westerly winds form in the stratosphere.

Sudden stratospheric warming (SSW) is when a rapid and dramatic rise in temperature occurs high in the stratosphere, roughly 10 to 30 miles (15-50km) above Earth's surface.

It can happen due to atmospheric disturbences causing a shift in the position or shape of the polar vortex which can make its winds weaken.

This sudden stratospheric warming (SSW) can eventually lead to the strong westerlies reversing into easterly winds.

In the following days and weeks these changes can slowly filter lower down in the atmosphere altering the position of the jet stream which drives what type of weather we experience on the ground.

Major SSW events have often historically increased the chance of drier and colder weather in the UK with northerly or easterly winds bringing in Arctic air.

It can also boost the possibility of snow, especially across eastern parts of the UK.

The 2018 Beast from the East followed a major SSW that occurred a few weeks earlier.

However, an SSW does not automatically lead to cold or snowy weather and any influence would take time to develop.

There are very few historical examples of early season major SSWs to compare with and so it is unclear exactly what, if any, impacts may happen a few weeks from now.

The previous earliest SSW on record happened on 28 November in both 1969 and 2025.

We do know that it is definitely not connected to the cold spell right now.

Because the stratospheric polar vortex operates at a global scale, disruptions and reversals can have impacts right around the world - increasing the possibility of cold weather, ice and snow in many regions, including North America.

However the possible impacts of this major SSW on the USA and Canada are, as in the UK, very uncertain.

There are historical examples of cold, snowy spells that can be linked - at least in part - to polar vortex disruptions.

The deadly winter storm that swept as far south as Texas in February 2021 followed a major SSW event that took place the previous month.

Widespread snowfall in February 2018, external was also linked to shifts in the polar vortex, and the same goes for the record 'snowmageddon' event that brought record-breaking snow to Washington DC in February 2010 - a winter when the vortex was unusually weak.

What these examples have in common is that they occurred in late winter - when polar vortex disruptions are most likely.

The difference this time is that the SSW has taken place unprecedentedly early - in the autumn - so its expected impacts are even less certain than normal.

Even if widespread northerly winds were to develop, the Arctic has not yet become as bitterly cold as it will be by late winter, so any chill spells may well be somewhat muted.

We are currently heading towards the expected peak of the strongest El Niño on record.

El Niño is a natural weather pattern that develops in the Pacific Ocean and the atmosphere above it.

When the winds that typically blow east-to-west weaken or reverse, warmer water can spread across the central and eastern tropical Pacific leading to changes in atmospheric conditions.

It is no surprise that the regions that see the most obvious weather impacts are the areas bordering this part of the Pacific, such as Peru and Ecuador in the east and Australia and Indonesia to the west.

However, El Niño can also affect weather patterns much further away.

In the UK, it means we tend to see a higher chance of wetter and stormier conditions in autumn and early winter.

There is also a higher chance of colder wintry weather developing late in the winter.

In the US and Canada there can be a greater chance of a warm and dry winter in northern areas and more risk of flooding rain further south.

There is also some evidence that El Niño can increase the likelihood of disruption to the stratospheric polar vortex which can, in turn, bring snowfall later in winter.

Any link between a strong El Niño and early onset of a SSW event, external is unclear and will need further research.

No two El Niños are the same. While it may increase the chance of certain types of weather occurring, this is not guaranteed.

Longer-range forecasting can give an idea of probabilities of certain weather patterns but there are always lots of different things going on and interactions between the atmosphere and oceans are complex.

These complexities are further compounded when happening against a backdrop of human-induced climate change.