In total, the Met Office warning covers 18 of Wales’ 22 council areas.
In south-west England, temperatures on Christmas morning were between 1C and 4C (34F and 39F) for most, said BBC Weather’s Matt Taylor, but it was “feeling below freezing due to the wind chill”.
Winds around coasts and on moors have exceeded 40mph at times, hitting 43mph at Plymouth and 49mph at Liscombe, Exmoor, he added.
Met Office spokesman Oli Claydon said it was “highly unlikely” the UK would see a white Christmas.
“We’ve got a very dry picture across the UK over the next few days,” he added.
Although not an official part of the UK, the crown dependency of Jersey experienced snow on Thursday morning.
The Jersey Met Section said it was only the third time since records began that snow was observed on the island on Christmas Day and the first time since 1970.