Sudden stratospheric warming: record event could hit UK

The Met Office says the event, which is expected to develop this week, could begin to influence weather across the country by late November.

If confirmed, it would be the earliest major SSW on record by around three weeks.

Alex Burkill, a presenter at the Met Office, said: "This looks like it could be a fairly major SSW and it could be the earliest major SSW on record by around three weeks.

"As a result, it's somewhat new territory for us.

"We don't exactly know how it's going to play out, what the high pressures will do, how they will be influenced by other factors.

"Likely that the El Niño is driving the earlier onset of an SSW, but it will also be playing a role in different ways.

"I just spoke about the fact that with this SSW occurring it means an increased likelihood of a blocking pattern as we go deeper into November and December."

SSWs occur when temperatures in the stratosphere rise rapidly—by as much as 50°C in just a few days—between 10 km and 50 km above the earth's surface.

Although the warming itself happens high above ground level, it can disrupt the jet stream and ultimately influence weather patterns further down.

These events do not happen every year and do not always impact surface weather.

The polar vortex, a band of strong westerly winds circling the Arctic in winter, can weaken or reverse due to SSWs, causing cold air to descend rapidly.

This in turn distorts the jet stream, often forming a blocking area of high pressure over the North Atlantic and Scandinavia.

Such a pattern typically leads to colder, drier weather in the UK and northern Europe, while southern Europe may experience milder, wetter, and windier conditions.

In some cases, the resulting easterly winds can bring snow, as was seen in early 2018 during the "Beast from the East."

Mr Burkill said that the timing of this SSW could alter the expected winter outlook.

He said: "But that's quite a contrast to what we were saying is most likely with an El Niño event for the UK, where previous El Niño events they often lead to milder, wetter, windier starts to winter and then something cooler and drier for the latter stages of winter.

"But now it looks like that cooler, drier period might come a bit earlier.

"And that's probably partly due to this El Niño being exceptionally strong."

BBC Weather has echoed the Met Office’s outlook, suggesting that the last week of November could see a transition to cooler, drier weather in northern areas.

A spokesperson for BBC Weather said: "The last week of November is more problematic, with competing atmospheric configurations indicated.

"A similar pattern may continue for most areas, but there is a chance of a cooler and drier development, at least in the north.

"Current happenings in the stratosphere might eventually play a role as the polar vortex is getting disrupted throughout early November, which is unusually or even uniquely early.

"If any effects were to filter down to the surface, it would take at least a couple of weeks, so that could be towards the end of November.

"It's nothing more than an outside risk at the moment but if this were to manifest then chiller weather could arrive."

While the outlook remains uncertain, both the Met Office and BBC Weather agree that a sudden stratospheric warming event could signal an earlier start to wintery conditions in the UK.