Scotland is on course for its coldest December in over a decade after the UK's lowest maximum temperature for 12 years was recorded in Aberdeenshire.
The Met Office confirmed the highest temperature recorded in Braemar was -9.3C after overnight temperatures plummeted to -15.7C.
BBC Weather's Simon King said it was the coldest night since February 2021.
A yellow warning for ice and snow currently covers northern Scotland with the cold spell set to last for 10 days.
A further yellow warning has been issued for the same area from midnight on Tuesday until 12:00 on Thursday.
BBC Scotland Weather reporter Kirsteen Macdonald said the 10-day cold spell would make it the coldest December since 2010.
She added: "Cold weather isn't at all unusual for the time of year but, given that we experienced a record-breaking mild November, this continued cold spell may come as a shock to people, at a time of great worry regarding energy bills and the cost of living crisis."
Meanwhile, about 2,000 properties across Shetland were without electricity on Monday evening after a power cut.
Residents faced a bitterly cold night as SSEN said supplies may only be restored by 11:00 on Tuesday.
Police Scotland said it was aware that people in the Burravoe and Bressay areas may not be able to make 999 calls from their landline but added that mobile phones should not be affected.
The extreme cold has also forced the closure of all schools and early learning settings across the isles on Tuesday, with the sole exception of Fair Isle.
Shetland Island Council confirmed the precautionary measure due to uncertainty over the impact the weather may have on school transport and power supplies.
The Met Office is also warning of ice and fog around the Solway Firth in Dumfries and Galloway.
It has led to a number of school closures in the Highlands and disruption to rail services.
Network Rail said icicles in tunnels were causing overhead line and signalling faults at Edinburgh Haymarket before they were cleared by staff.
ScotRail has reported "disruption across the network".
Many rural areas saw temperatures dip to minus double figures.
Balmoral came in at -13.5C, followed by Aviemore at -13.0C, Dalwhinnie at -12.0C, Kinbrace at -11.2C, Fyvie Castle at -11.0C, Altnaharra at -10.5C, and both Tulloch Bridge and Drumalbin at -10.1C.
In Glasgow temperatures fell to -7.2C and to -6.7C in Edinburgh.
Snowfall caused the closure of the snow gates at the A939 at Cock Bridge and the A939 at Tomintoul.
In Dumfries and Galloway, Drummore School near Stranraer and Penpont School have been closed due to snow and ice issues, while police are warning people not to try to walk on parts of the River Nith which have frozen in Dumfries.
Graeme McLatchie told BBC Scotland how he was forced to spend the night at Luton airport after his flight to Glasgow was cancelled.
He said: "We were supposed to be on the 6pm from Luton back to Glasgow, with EasyJet. They eventually cancelled the flight after 11pm with little-to-no communication, along with other flights to Inverness and Aberdeen.
"I understand the weather conditions made it difficult but it was all done so late that there was no option but to sleep at the airport."
Mr McLatchie, 44, who lives in Paisley, is now on the train back to Scotland.
Clear skies gave us a good view of snow cover over mainland Scotland today 🛰️ ❄️
…on (provisionally) the coldest UK day since Dec 2010 🥶 pic.twitter.com/EUavHDdsy3
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