Polar Vortex Winds Reverse in Earliest Sudden Warming on Record

The winds of the polar vortex high above the Arctic have reversed direction, marking the earliest “major sudden stratospheric warming” (SSW) on record, the BBC reports. Observations now show the usual westerly winds have switched to easterly, which is what defines a major event.

Disruptions like this can happen in winter and are often followed by colder weather in the UK. One this early in autumn is unprecedented in modern observations, according to the BBC. What it will do to the weather in the coming weeks is not known.

What a sudden stratospheric warming is

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

In an SSW, the temperature in the stratosphere, roughly 10 to 30 miles (15-50km) above the surface, rises rapidly. Disturbances in the atmosphere can shift the position or shape of the vortex and weaken its winds. Eventually the westerlies can turn into easterlies. Over the following days and weeks, the change can work its way lower in the atmosphere and alter the position of the jet stream, which steers the weather people feel on the ground.

In recent weeks the vortex weakened and shifted position before the reversal was confirmed by observations.

Could it bring snow to the UK?

Major SSW events have historically raised the chance of drier, colder weather in the UK, with northerly or easterly winds bringing Arctic air. Snow becomes more likely, especially in eastern parts of the country. The 2018 Beast from the East followed a major SSW that happened a few weeks earlier.

The BBC stresses that an SSW does not automatically produce cold or snowy weather, and any effect would take time to develop. Very few early-season major events exist for comparison, so the impacts are unclear. The previous earliest SSW on record happened on Nov. 28, in both 1969 and 2025.

The BBC also says the event is definitely not connected to the cold spell happening now.

What the Met Office is watching

Longer-range forecasts made a few weeks ago pointed to a wetter and stormier late autumn and early winter than average, consistent with an El Niño pattern. That was welcome news for farmers, water companies and the roughly 30 million people still covered by a hosepipe ban. Much of England and Wales remains in drought or severe drought.

The Met Office still expects a similar unsettled pattern at the start of winter, the BBC reports, though the stratospheric changes may have slightly weakened the signal for a wetter November. The Met Office also sees “tentative indications” that the SSW could contribute to a storm track shifted further south in December.

Where El Niño fits in

The world is heading toward the expected peak of the strongest El Niño on record, according to the BBC. El Niño is a natural pattern in the Pacific Ocean and the air above it. When the winds that normally blow east to west weaken or reverse, warmer water can spread across the central and eastern tropical Pacific, changing conditions in the atmosphere.

The most obvious effects are in places bordering that part of the Pacific, such as Peru and Ecuador in the east and Australia and Indonesia in the west. It can also change weather much farther away. In the UK it tends to raise the chance of wetter, stormier conditions in autumn and early winter, and of colder weather late in winter.

Whether a strong El Niño is linked to the early arrival of this SSW is unclear and needs further research. No two El Niños are the same, and one can raise the odds of certain weather without guaranteeing it. Long-range forecasts give probabilities, and the ocean and atmosphere interact in complex ways, made harder to untangle by human-induced climate change.

What this means for readers

The reversal itself is an observed fact, but its effect on UK weather this winter remains an open question. Readers in the UK can follow Met Office forecasts and official warnings, and listen to local authorities, for the weather expected where they live.

Source: BBC