Overnight, the temperatures will drop sharply, reaching potentially minus 16°C in the Highlands.
Oli Claydon, a spokesman for the Met Office, told PA News that Thursday night will be “bitterly cold”.
He also noted that the lowest temperatures are likely to occur in rural Scotland, which is still under an active yellow warning until Thursday night.
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Dalwhinnie, a small village in the Scottish Highlands and on the western edge of the Cairngorms National Park, will experience a sharp minus 14C – the lowest temperature registered since January 17, 2024.
However, Altnaharra in the Highlands is expected to experience an overnight low of minus 16°C, marking the coldest January temperature in the UK in 15 years.
The coldest temperature in the UK was recorded in Braemar, Aberdeenshire, in February 2021, when it dropped to minus 23°C.
Dr Agostinho Sousa, head of extreme events and health protection at the UKHSA said: “This weather can have a serious impact on the health of some people, including those aged 65 and over and those with pre-existing health conditions, and it is, therefore, vital that we continue to check in on friends, family and neighbours that are most vulnerable.
“These people could be more at risk of heart attacks, stroke and chest infections as a result of cold temperatures.”
Wales, Northern Ireland and northern England are also facing freezing temperatures, and an amber weather warning was put in place over Cornwall.
Oli Claydon, spokesman for the Met Office, told the PA news agency that the weather will get gradually milder over the next few days.
“Certainly by the end of the weekend, we’re moving to a milder air mass and it’ll slowly get introduced across the UK through Sunday,” he said.
“By Monday, the UK will broadly be in a milder air mass and we’ll see some rain moving in from the North West into parts of western Scotland and potentially Northern Ireland as well.”