Frost and sunshine on Christmas Day will turn to wind and rain over the following 24 hours, the Met Office has said.
Much of the UK will wake up to frost and fog on December 25, before the wintry weather lifts to make way for sunshine later in the day.
But the pleasant conditions will be short lived, with rain and and wind forecast for parts of the UK throughout Boxing Day.
The Environment Agency has also warned of potential flooding across England, due to further wet weather later in the week.
Met Office forecaster Helen Roberts said: “Boxing Day goes downhill a bit, with rain pushing in from the west and gradually transferring north east.
“There will be spells of rain for everyone and it will be quite breezy, with gales around the western coasts pushing inland.”
England’s south-western coast is forecast to be hit by 40mph to 45mph winds, which will reduce to 15mph to 20mph further inland.
A band of rain will also sweep in from the West, pushing into the North East by the late morning, the Met Office said.
Temperatures on Boxing Day will be mild, reaching 11C in the South West and up to 9C in the midlands.
As of 12.30pm on Tuesday, the Environment Agency has issued 43 flood warnings, where flooding is expected, and 114 flood alerts, where flooding is possible.
The agency’s flood duty manager Carol Holt said: “Following wet weather over the past week and with more rain forecast, there is a continued risk of flooding in large parts of England over the festive period.”
She said about 100 properties have been flooded since Thursday, adding that more than 18,500 properties have been protected by flood defences.
More rain is forecast for Friday in the North West and across parts of western Scotland, while the south east of England will be “generally drier”, the Met Office said.
Before the arrival of the pleasant conditions on December 25, the Met Office is predicting that thunderstorms will hit parts of south Wales and south-west England on Christmas Eve.
A severe yellow weather warning has been issued which says there may be damage to a few buildings and power outages, with delays to journeys by rail or road also possible.
On Christmas Day morning, temperatures in Scotland are forecast to fall to lows of minus 3C and about 0C in England and Wales.
That will increase to about 7C in northern parts of the UK and 8C in the South, the Met Office said.
The thickest of the morning fog is likely to be in Wales and central and western parts of England.
“Christmas Day is looking like a lovely day for pretty much the whole of the UK,” Met Office forecaster Greg Dewhurst said.
It is highly unlikely there will be any significant snowfall this year, Mr Dewhurst said, adding: “If there is any snow it will be over the tops of Scottish mountains, which we don’t class as a white Christmas.”