The whole of Scotland has been warned to brace for snow after a weather warning issued on Monday for the North east was extended to cover the rest of the country.
Forecasters predicted a bitterly cold night for many, with temperatures plunging to -4C in towns and cities and even lower in rural areas.
A yellow warning is in place for snow and ice across Scotland, lasting 72 hours from midnight on Monday.
Travellers have been urged to take care and plan journeys carefully. Transport Scotland said it had "well-established plans" that were now in effect to minimise disruption.
Head of transport resilience, Stein Connelly, said a multi-agency response team would be working to co-ordinate resources.
Around 200 schools across Aberdeenshire, Moray and Shetland were closed due to snow on Monday.
More than 100 schools were closed on Tuesday amid the wintry weather.
There were 22 school closures in Aberdeenshire while almost all other schools were either opening late, facing transport issues or were partially closed.
In the Highlands, 75 schools were closed while others were partially closed or had delayed openings.
Twenty-six schools in Shetland were closed
The Met Office said heavy snow is possible across northern areas on Tuesday, with the rest of the UK seeing a cold, dry day ahead of a widespread, severe frost in the evening.
Mr Connelly said: "This cold snap is already causing difficult driving conditions, with further severe impacts anticipated on Tuesday as part of the existing warnings.
"It's important that anyone that has to travel during the warning period plans their journey in advance and allows extra time.
"If you have to travel, please drive to the conditions. There may also be disruption on other modes of transport, so please check before setting off."
Northern and eastern parts of Scotland saw the “bulk of the snow” on Monday, with 15cm on the ground at Aberdeen Airport by the evening.
A “cold plunge of Arctic air” has moved south across the whole country over the past few days, making it 5C to 6C lower than usual for this time of year, the Met Office said.
Met Office forecaster Craig Snell said Tuesday could see a “persistent band of snow” over three to six hours across Scotland, Northern Ireland and parts of northern England and Wales.
He said: “In the early hours of the morning we’re looking at temperatures getting down to -12C in a few spots, Tuesday night possibly down to -15C.
“So certainly a very cold spell into Wednesday.”
Roads maintenance group, Amey North-East, said that 19 gritters were treating roads and 13 vehicles would be on patrol overnight into Tuesday morning.
In the south of the country, Bear Scotland said it had treatment plans for all routes in place.
Police Scotland head of road policing, Ch Supt Hilary Sloan, urged drivers to consider whether their journeys were necessary.
She said: "If you absolutely have to travel, please drive to the conditions, be prepared for delays and allow extra time for your journey.
"Please don't drive through road closures, the decision to close roads is not taken lightly and is done for public safety."
Met Office Chief Meteorologist, Andy Page, said: “Where and how much snow we will get will vary throughout the week and weather warnings could change quickly, you will need to keep an eye on the forecast for your region for the latest information.
“There will be widespread frost this week and we could see some fairly deep laying snow in parts of northern UK and strong winds could result in drifting or blizzard conditions at times.
"The snow and ice will be disruptive and could potentially impact travel plans, make driving dangerous and pavements slippery.
“It will feel bitterly cold with daytime temperatures in the low single figures for many, and overnight temperatures will fall to -3C or -4C (24-26F) in many towns and cities, and it will be even colder in many rural areas.”
Network Rail Scotland said specialist forecasters, infrastructure teams and train operators held an "extreme weather action meeting" on Monday to plan for train services in Scotland.
It said de-icing fluid would be applied to keep critical junctions open and "proactive changes" on the Highland main line had already protected remote junctions from signal failure.
ScotRail said services on the line, from Perth to Inverness, would be delayed by around 30 minutes all day on Tuesday.
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