It comes after freezing conditions recently gave way to unseasonably balmy weather for December.
The UK has seen a wild swing in temperatures over the last week with an ‘extraordinary’ rise of almost 20 degrees celsius in just a few days.
But from Boxing Day, a wave of arctic air will bring ‘colder conditions’ amid potentially more snow and frost.
James Madden, forecaster for Exacta Weather, told GB News: ‘The rest of December and January are showing signs of frequent spells of cold wintry weather with below-average temperatures and numerous wintry blasts.
‘We could now be looking at a lengthy cold period setting in for a number of weeks and the potential for some of the coldest and snowiest weather since December 2010.’
The Met Office’s long-range forecast echoes the comments made by Mr Madden.
From Boxing Day onwards, the UK should expect ‘uncertainties’ and ‘colder conditions’.
‘Some wintry showers are also possible, especially in coastal areas.’
The cold snap will come after December 25 – meaning odds of a White Christmas are dashed for many.
Experts are now forecasting that the date will most likely be mild with a risk of rain or showers in places for the south, especially the far south.
Any cold air and wintry conditions will most likely be confined to the north of the UK, they add, but caution that their predictions could change as Sunday is still five days away.
Met Office deputy chief meteorologist, Dan Harris, said of the north-south split: ‘There are large uncertainties concerning where the boundary between these two air masses will eventually end up, especially as we head into the Christmas weekend.
‘Confidence in the forecast is unlikely to increase until mid-week at the earliest and a range of outcomes are still possible.’