Temperatures could rise as high as 14C (57F) in parts of Britain on Monday, the Met Office has predicted, but the warmer weather will bring the risk of flooding.
Most of south Wales, south-west England and some of the south-east are under a yellow warning for rain, with the risk of some flooding. Surface flooding may also occur in other parts of the UK as snow and ice on higher ground melts overnight.
A yellow warning for ice was in place across northern England on Sunday evening, with freezing rain and snow making travel conditions dangerous.
In the yellow warning area, which covers most of Yorkshire, the north east and north west, freezing rain could lead to a build-up of 2-3mm of ice on untreated surfaces, the Met Office said, which could cause treacherous travel. conditions and road closures.
“Obviously we’ve had very cold air from the north and the Arctic for a week, 10 days or so, but now we’re starting to see Atlantic air coming back from the southwest,” Met Office meteorologist Marco Petagna said.
“We are set to see a big change to much milder weather [on Sunday]when we look at temperatures in the double digits.”
Sunday was a “transition day”, he said, with an amber warning in northern England in place until midnight and warming temperatures expected to start melting snow and ice overnight.
The west coast of Wales was forecast to have the warmest weather on Monday, reaching as high as 14C.
It is unusual for a change in temperature from several degrees Celsius below average to several degrees above, Petagna said.
“Temperatures climbing overnight is an unusual feature. Of course, in winter, we would normally see temperatures drop overnight, but with the milder air coming in, temperatures will rise.”
However, the warm weather is unlikely to last until Christmas Day, the Met Office said.
Petagna added: “At the end of the week there is a hint that we may have some cold weather coming back from the north, but there is a lot of uncertainty about how far south it will spread and how cold it will be. It is some distance away, and a lot can happen in the meantime.”