The arrival of a freezing weather system from the Atlantic threatens to bring snow to large parts of Britain over the coming days, forecasters are warning.
The Met Office says that following the unseasonably mild start to the year, temperatures are set to plunge to below freezing in some places, with overnight frosts and possible snow showers forecast from Wednesday onwards.
In the west of England and Wales, expected rain showers could turn to snow by Friday, while average daytime temperatures in the south of England will struggle to rise above 6C, the London Evening Standard reports.
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And the mercury could drop as low as -5C further north and in rural areas of Scotland.
The Met Office says the cold weather is related to the disruption of the polar vortex, a swirling area of cold air that circles above Earth’s two poles.
If left undisturbed, the polar vortex remains in place and usually dissipates in late spring, explains US-based magazine Popular Science. But each year a period of “sudden stratospheric warming” may see waves of warm air intrude on the vortex.
If this happens, the disrupted vortex may occasionally shift south or - as has happened this week - split into multiple smaller vortices, displacing cold weather across the “mid latitudes” of the planet that covers western Europe, northeastern US and northern Asia.
Met Office meteorologist Bonnie Diamond said the result for the UK is that cold polar air from the northwest will switch to a colder Arctic airflow from the north.
“Through Wednesday a polar maritime air mass is going to push in from the west, but by the time we get to Thursday it will be an Arctic air mass,” she said.
Deputy chief meteorologist Martin Young added: “The latest forecast suggests the highest risk of any severe wintry weather is from late January and into February.
“From the middle of this week, and especially during the last week of January and into early February, there is an increased likelihood of cold weather becoming established across all of the UK.”
However, the Met Office also says the current meteorological event causing the potential cold snap is “burrowing down through the atmosphere relatively slowly”, meaning the UK should not see temperatures drop as far or as quickly as last year’s so-called Beast from the East, which brought heavy snowfall.
