The Met Office has issued a yellow warning lasting from 11:00 GMT on Friday until 06:00 on Saturday
Snow could cause disruption across large parts of the UK later, the Met Office has warned.
An "area of rain, sleet and snow" will move east across Northern Ireland, central and northern England and Wales and part of southern Scotland.
Where snow falls there could be "several centimetres even at low levels", and more than 10cm (4in) is "possible", the Met Office said.
But "a lot of uncertainty surrounds how much snow will occur", it added.
A yellow severe weather warning - meaning "be aware" - has been issued for all the affected areas.
The Met Office said there was "potential for disruption from snow", especially for people travelling.
"A depression developing over the Atlantic Ocean is expected to track east then south-eastwards across the southern half of Britain during Boxing Day," it said.
Much off the UK - including Formby Point in Merseyside - saw some sunny weather on Christmas Day
There was also Christmas sunshine at Boscombe Beach in Bournemouth
"A spell of snow is likely, even to lower levels, on the northern flank of this depression. South of the depression centre, rain will fall, heavy at times.
"There remains much more uncertainty than average regarding the track of this depression which in turn leads to uncertainty about the location of the heaviest precipitation and how much snow there will be."
The weather system is expected to move across the country before "clearing during [Friday] evening and overnight" - though the weather warning applies from 11:00 GMT on Friday until 06:00 on Saturday.
BBC Weather forecaster Jay Wynne said there would be "quite a bit of variation from location to location on how much now you see".
Forecasters have also warned of freezing temperatures in the days leading up to New Year.
The Met Office said there was an 80% chance that cold conditions could "increase the health risks to vulnerable patients and disrupt the delivery of services".