Parts of Britain recorded sub-zero temperatures today with schools being forced to close and motorists facing chaos on the road.
In Aberdeenshire, Scotland, there were reports of thundersnow - described as a snowy thunderstorm - and cold weather is set to continue over the next few days.
When thunderstorms form in wintry conditions they can sometimes give rise to heavy downpours of snow.
If thundersnow occurs at night, the lightning appears brighter as the light reflects off the snowflakes, the Met Office explains.
Today, it was announced that a snow and ice yellow warning across northern Scotland has been extended until 12am on Sunday.
Some roads and railways are likely to be affected with longer journey times by road, bus and train services.
Two separate yellow warnings for ice also cover large parts of England, Wales and Northern Ireland.
The Met Office said disruption is likely due to icy surfaces on roads, pavements and cycle paths.
There is also a risk of injuries from slips and falls due to ice, Brits have been warned.
This morning forecasters confirmed that there had been 5cm of snow in Aboyne, Aberdeenshire, and at Althnaharra in the Highlands, along with 3cm at Dyce, near Aberdeen.
Met Office chief meteorologist Steve Willington warned there is an "increasing risk of snow as the week progresses".
Mr Willington said: "As an Arctic, maritime airmass settles across the UK, temperatures will fall with widespread overnight frosts, severe in places, and daytime temperatures only a few degrees above freezing.
"However, the cold air from the Arctic will also bring brighter conditions, with some dry, sunny spells, particularly away from the coast and where winds are light it could feel pleasant in the sunshine. Some patchy freezing fog is also likely."
An Aberdeenshire Council spokesperson said: "Our gritting fleet has been treating all our primary routes this afternoon and will be out again tomorrow morning, as we are expecting wintry showers to continue overnight, with road temperatures falling below zero.
"While there have been no significant impacts today, the snow and ice has led to the closure or partial closure of some of our schools, mostly due to transport difficulties.
"We'd ask everybody to plan ahead if they have a need to travel, and to follow the latest weather forecasts."
With more snow forecast to fall in the next few weeks, mountain safety organisations are coming together to encourage people to "ThinkWinter" and ensure that those heading for the hills and mountains can easily access the right information and advice on safety in the winter months.
Scottish Mountain Rescue chair, Bill Glennie, said: "Do go out into the outdoors and enjoy Scotland's mountains when many would say they are at their finest, but do it safely, with the appropriate skills and equipment."
Mountaineering Scotland's senior mountain safety adviser, Ross Cadie, added: "When winter arrives in Scotland's mountains, we need to make sure we do our homework before heading out.
"Planning and preparation from trusted sources and matching your adventure to your level of skill and conditions will help you return home safely."
The Met Office's long-range forecast from December 13 to December 22 says snow showers are expected to continue across the northeast of the UK, with an increase in cloud cover in the southwest.
Some areas across the south could see a mixture of cloud, winds, rain and snow, the forecast adds.
The end of the month will continue to be cold with temperatures below normal, but they may increase in the south towards the end of 2022.
UK 5 day weather forecast
This Evening and Tonight:
Wintry showers over northern Scotland and exposed coasts elsewhere, occasionally moving inland, with further snow accumulations and icy surfaces. Clear spells elsewhere with some patchy freezing fog and a widespread frost, severe in places.
Friday:
Cold with widespread frost, perhaps some early isolated freezing fog. Wintry showers continuing near exposed coasts. Many inland areas remaining dry. Winds mostly light, moderate along exposed coasts.
Outlook for Saturday to Monday:
Staying cold or very cold, with further wintry showers, mainly for coasts. Freezing fog is also likely in places, this slow to clear. Severe frosts likely by night.
