Britons are being warned of Boxing Day travel disruption as rain turns to snow, threatening road and rail delays.
After those dreaming of a white Christmas Day had their wishes granted in parts of the UK, the Met Office said more wintry showers are expected on Tuesday and Wednesday.
The forecaster said temperatures would turn colder on Boxing Day and there is the chance of 4in (10cm) of snow on the highest ground in Scotland.
Despite a largely mild Christmas Day - the highest temperature recorded was 12.6C (54.6F) in Bude, Cornwall - weather warnings for snow and ice are in place on Boxing Day for southern, central and eastern Scotland, and the most northern parts of England.
A further warning for rain and snow is in place for the Midlands and Wales running from 6pm on Tuesday until 11am on Wednesday.
The Met Office warned that roads and railways "likely to be affected by longer journey times due to standing water or snow". It added there is also a chance that homes and businesses could be flooded.
Spadeadam in Cumbria and parts of southern Scotland saw rain turn into snow at about 10pm on December 25.
The last officially white Christmas was recorded in 2014, when parts of Scotland had some snowfall.
AMet Office weather warning for snow and ice is in force for between 7pm on Christmas Day to 11am on Boxing Day.
Warning that temperatures will fall with a risk of ice and snow in some areas, it said: "Rain will turn to sleet and snow in parts of southern, central and eastern Scotland, as well as the north Pennines, with further wintry showers in places overnight.
"So a cover of snow in places, chiefly over high ground (0-2 cm over some low ground, 2-5 cm above 200 m elevation and perhaps 10 cm on the highest routes). Ice is looking to become more widespread later as skies begin to clear into Boxing Day.
"Some roads and railways may be affected by longer journey times, with icy surfaces leading to the possibility of slips and falls on roads, pavements and cycle paths."
Another Met Office yellow weather warning for rain and snow has been issued for between 6pm on Boxing Day until 11am on Wednesday.
Warning of heavy rain turning to snow in places, it said: "An area of heavy rain will extend north and east across the area later on Tuesday and last though Tuesday night, easing away from eastern areas on Wednesday.
"The rain is likely to turn to snow in places, initially across Wales and then across parts of central England and eventually some of the higher ground in counties north and west of London.
"Some roads and railways are likely to be affected by longer journey times due to standing water or snow. There is also a smaller chance that individual homes and businesses could be flooded."
Met Office forecaster Mark Wilson said temperatures would turn colder on Boxing Day, with averages of 2C and 4C in Scotland and between 7C and 9C in the south of the UK.
Speaking on Monday night, he said: "To be a white Christmas, we only need to see one flake but we have reported snowfall in Spadeadam for the last couple of hours.
"It will turn a bit colder - but nothing like the temperatures we saw earlier this month - I think it would be fair to describe the Boxing Day temperatures as 'around average'.
"Two to four degrees (35-39F) in Scotland and seven to nine in the south. It will start bright, but there will be some wet weather in the south west and it will meet cold air over Wales and the Midlands towards the end of Boxing Day."
For years, Christmas was declared "white" if a single flake of snow was observed by a professional meteorologist falling on the roof of the London Weather Centre.
The Met Office has now broadened its definition to extend to other parts of the country, although the snow still has to be recorded by a professional.
HOT OF THE PRESS - Spadeadam (in Cumbria) has recently reported light snow. Parts of southern Scotland are also seeing rain turning to snow. This has officially made it a white Christmas for some (just in the nick of time!)— Met Office (@metoffice) December 25, 2017
The high of 12.6C is a few degrees off the record for the warmest Christmas, when 15.6C (60.08F) was recorded at Killerton, Devon, in 1920.
And while mild, it was still chillier than last year when temperatures reached 15C (59F) in a number of places including Hull, east Yorkshire.
It was estimated that 11.5 million leisure trips will have been made by car between December 17 and Christmas Eve.
But this is expected to be eclipsed by the 17.5 million between Christmas Day and New Year's Day as people take advantage of post-Christmas sales at shops.
Airports will also be exceptionally busy over the festive period , with more than 4.5 million people expected to head abroad over Christmas and the new year.
Latest travel information
The Highways Agency has lifted almost 400 miles of roadworks due to take place over the Christmas and New Year period to ease festive congestion.
Highways England’s customer service director Melanie Clarke said: "We’re doing everything we can to make journeys as smooth as possible this Christmas and that’s why we’re keeping 99 per cent of the road network we manage free from roadworks."
Major improvement works on Britain's rail network will be undertaken during Christmas and into the New Year.
Many of Britain's mainline routes will be partially shut as Network Rail carries out its biggest ever Christmas investment programme.
Great Western Railway
London Paddington will be closed between Christmas Eve and December 27. Passengers are being urged to complete journeys by Saturday "at the latest".
The West Coast
The West Coast main line will be halted between Preston and Lancaster from Christmas Eve to December 27, with buses replacing trains.
London and Glasgow
Passengers travelling between London and Glasgow during this time are advised to go via Edinburgh, adding around an hour to journeys.
Southeastern, which serves London, Kent and East Sussex, will not be able to run trains to London Bridge, Charing Cross and Cannon Street between Saturday and January 1.
Strike action by Virgin Trains workers over pay has now been called off after talks.
Merseyrail said it will run a reduced service across its network on Friday, with RMT members pressing ahead with a 24-hour stoppage in a dispute over the role of guards.
Abta, the travel trade organisation, has urged flyers to allow extra time to get to the airport during the period from December 18 to January 2.
Tips for travelling
Issuing a warning to travellers, the Met Office said: "The secret to a successful and stress-free Christmas is planning and preparation.
"Just as you wouldn’t want to buy your presents in a Christmas Eve panic, it’s never sensible to leave planning your travel arrangements until the last minute either.”