Monday could bring highs of 14ºC or 15ºC in south-west England and northern Wales, after freezing conditions in recent days, a Met Office meteorologist said.
It comes after minus 17.3ºC was in recorded Braemar in Scotland on Tuesday — the coldest temperature since February 11, 2021 — while other places around the country experienced lows of between minus 10ºC and minus 15ºC in recent days.
The forecasting service has issued yellow weather warnings for rain across southern parts of England and southern Wales from 6pm on Sunday to 6am on Tuesday.
It said heavy rain could flood some roads, homes and businesses, and cause travel disruption.
“It’s also worth bearing in mind that, preceding this obviously it was so cold, so the grounds were a bit frozen, drains may have been frozen in places,” said Met Office meteorologist Alex Burkill.
“As a result, their ability to cope with the rainfall may have been reduced, so that’s why we could see some greater impacts, which is why the warning was issued.
Snow blankets the UK, with more wintry weather to come - in pictures
“The drastic change to something milder is going to be pretty widespread, perhaps south-west England, maybe even north Wales could get 14ºC or 15ºC.
"Elsewhere though, widely temperatures are going to be in the 12ºC to 13ºC bracket on Monday."
But Mr Burkill on Sunday said northern Scotland could see temperatures in the single figures on Monday.
“Monday night into Tuesday, for most it’s going to be a lot milder than it has been of late but we could still see a touch of frost, particularly in parts of Scotland," he said.
“And then Tuesday, I think it’s going to be a little bit colder again compared to Monday. So the really mild day, Monday, is a flash in the pan, if you will.
“I think we’re still looking at highs of 12ºC perhaps 13ºC towards the south coast.
"But away from that, as you head to more central parts and further north, we’re going to be in mid-to-high single figures at best, so quite a drop compared to Monday.
“The cold period lasted so long and was so extreme, that’s come to an end.
“But I think it’s fair to say the really mild weather we’ve got through tonight and into tomorrow is going to be very short-lived.
Cold weather in the UK – in pictures
“Things have gone from well below average, tomorrow they go to quite a bit above average and then they return closer to average as we go through tomorrow night onwards.
“What I’m expecting in the run-up to and through Christmas weekend is for southern parts to have temperatures near normal, northern parts to be a little bit colder, and there will also be some changeable weather coming through.
"So with that you could quite easily get some wintry weather as we go towards Christmas, mainly towards the north."
A major incident was declared in Shetland after more than 5,000 homes lost power on Monday afternoon as heavy snow brought down lines.
But all properties were reconnected as of Sunday, Scottish and Southern Electricity Networks Distribution said.