"Blizzard conditions" hit northern parts of the UK over higher ground on Sunday, as heavy rain and snow moved into some regions.
The Met Office issued yellow weather warnings for snow until midday Sunday in parts of northern England, as well as southern and central Scotland.
The most severe snow was expected over higher ground - with up to five to 10cm in some areas.
Scottish areas affected included Clackmannanshire, Falkirk, Perth and Kinross, and Stirling.
Strong winds of up to 35 to 45mph in places led to difficult travel conditions across higher Pennine and Cumbrian routes, as well as the Southern Uplands.
The A66 was shut earlier after overnight snowfall between Scotch Corner in north Yorkshire and Brough in Cumbria made the route impassable. Improved conditions enabled the road to reopen in the afternoon.
"Temporary blizzard conditions may be encountered above around 300 or 400 metres elevation," the Met Office said earlier.
"These conditions will probably move into some hillier central parts of Scotland during Sunday morning, while snow turns back to rain further south."
The Met Office said some "short term" loss of power and other services was possible during the period of the warnings.
Meanwhile, a yellow rain warning was issued for County Armagh and County Down in Northern Ireland until 9am on Boxing Day.
Between 25mm and 40mm of rain was forecast, with up to 60mm possible.
After the recent wet weather there, local flooding is a risk.
The Met Office confirmed it had been a white Christmas in parts of the UK, with people waking up to snow in Shetland, Aboyne, Strathallan and parts of the Pennines.