Forecasters have said the cold snap would continue for the next few days
Fresh travel warnings have been issued as the wintry conditions continue to cause problems on Scotland's roads.
It was another night of freezing temperatures, with lows of -18C in parts of the Highlands.
The runway at Inverness Airport was shut earlier because of snow and ice but has reopened for arrivals and departures.
ScotRail said services in and out of Glasgow Central have been reduced because of the severe conditions.
Caledonian MacBrayne said technical problems with the Isle of Lewis ferry meant another vessel, the Clansman, has had to take over the Ullapool and Stornoway service while repairs are carried out.
The Met Office has issued warnings of widespread icy roads and heavy snow in the Highlands, Western Isles and the north east.
It said severe snow showers would affect parts of Moray, Nairn and the Inverness area.
Temperatures plunged to -18C at Braemar in Aberdeenshire - the coldest night so far this winter.
At Tyndrum in Stirlingshire the mercury dropped to -17C while at Strathallan in Perthshire it was -16C.
Crews from Highlands and Islands Fire and Rescue Service were called out to remove large icicles hanging from buildings in Grantown on Spey after they were deemed a danger to pedestrians walking below.
The Maritime and Coastguard Agency has also warned people against venturing out onto frozen lochs after a man fell through ice while skating at Shawbost on Lewis on Sunday.
Scottish ministers urged people to take extra care, after the NHS reported a rise in the number of people injured in falls.
NHS Grampian said that since Christmas Day between 20% and 25% of people arriving at the Accident and Emergency department at Aberdeen Royal Infirmary had fractures, compared to about 10% normally.
Flocked to slopes
NHS Lothian also reported an increase in the number of people with fractures and dislocations as a result of slips and falls in the past week.
Justice Secretary Kenny MacAskill said: "Temperatures are forecast to plummet again tonight, so we can expect icy roads and pavements and possibly some further snow in the west.
"I'd therefore encourage everyone to be especially careful when out and about - either on foot or behind the wheel - to minimise the risk of accidents."
However, the Scottish ski industry said the snow and sub-zero temperatures had helped it experience its best start to the season for years.
Thousands of skiers and snowboarders have flocked to the slopes at Cairngorm, Glenshee and the Lecht, and the operators of the Nevis Range centre near Fort William said conditions could not get much better.
The Glencoe ski area was open for business for the first time since the centre closed earlier this year amid fears about its future.
Forecasters have predicted that the cold snap will continue for the next few days, with the possibility of more snow in some areas.