A weakening polar vortex could bring Arctic air and wintry conditions to the UK later this month.
The polar vortex is a band of strong winds high in the atmosphere that typically keeps cold air trapped near the North Pole.
If it weakens, there is a greater risk of colder air pushing south into the UK.
Marco Petagna, a forecaster at the Met Office, said: "At the moment, we've got a warming taking place in the stratosphere.
"The polar vortex in the stratosphere is starting to weaken."
Most of this morning's fog will clear to leave some sunshine this afternoon ⛅ However, thicker cloud will give patchy rain in the north and east, with a few heavy showers across the far south of England https://t.co/s4OhPGTrVr
— Met Office (@metoffice) November 7, 2026
If the winds reverse, it could become a "major sudden stratospheric warming" event—potentially the earliest ever recorded.
Mr Petagna said: "For the UK, it does increase the chance of cold weather, normally a few weeks down the line, so sort of deeper into November is when we're more likely to see an influence if it does happen.
"It's important to emphasise that there was a major warming event last November, and on that occasion it didn't directly lead to much cold weather in the UK.
"It doesn't always happen, it just increases the chance of it occurring."
Forecasters will continue to monitor the polar vortex over the coming weeks to assess the likelihood of colder conditions reaching Britain.
In the short term, a yellow fog warning is in place across parts of the South West, South East and Midlands on Sunday morning, potentially disrupting travel for those heading to Remembrance services.
Visibility could plunge below 50 metres in places, and conditions should improve through the day, with sunshine breaking through, gentle winds and temperatures around 9C or 10C.
Monday is expected to start foggy again before rain and stronger winds spread across the UK on Tuesday and Wednesday.
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