Travellers are being warned of a high risk of disruption as snow and ice affect large swathes of Scotland.
The Met Office has issued an amber alert for south west Scotland, extending to parts of the central belt, lasting until Wednesday morning.
More than 10,000 pupils missed lessons on Tuesday as scores of schools up and down the country were closed.
Thundersnow is also forecast in the west, with a warning that power supplies may be affected.
Police Scotland said anyone taking to the roads in the worst affected areas was “highly likely” to experience disruption, and urged drivers to consider carefully if the journey was necessary.
A Multi Agency Response Team (Mart) is now operational to monitor conditions. The deputy first minister and transport minister also chaired a meeting of the Scottish government’s resilience operation to receive an update on the situation.
Transport Minister Humza Yousaf said: “The Met Office has upgraded its snow warning for parts of south west and central Scotland, with the areas affected by the amber warning set to see heavier snowfalls and greater disruption to transport.
“The snow and ice is likely to lead to difficult driving conditions, so I’d urge all travellers to take extra time and plan their journeys in advance. The high winds forecast for later in the week may also see some bridge restrictions.”
The Met Office amber “be prepared” warning – which means transport and power supplies may be disrupted with a potential risk to lives and property – was issued from 15:00 on Tuesday until 08:00 on Wednesday and also extends across much of Northern Ireland.
and at least 13 schools were closed.
Longer spells of snow are expected, especially on Tuesday evening, with drifting over the hills in strong to gale force winds before the situation improves on Wednesday.
Areas in Scotland affected by the amber warning include Central, Strathclyde, south-west Scotland and Lothian, the Borders and some parts of Tayside and Fife.
Some high ground is likely to see 15-25 cm (6-10 inches) of snow building up, especially above 200-300m, with 5-10 cm (2-4 inches) more typical at low levels throughout the warning area.
Yellow warnings of snow are likely to remain in place across most of the country until late on Friday.
A number of roads were affected by snow and ice during the morning rush hour, including the A9, M9, M80, A720 M77, M74, A7 and the M73.
Drivers travelling from Glasgow to Edinburgh were asked to avoid the M8 due to long delays.
And difficult driving conditions led to a number of minor shunts across the country’s roads network.
Latest snow depths, as of 1pm.
— BBC Scotland Weather (@BBCScotWeather)
Thousands of school pupils .
The weather affected 13 secondary schools, 53 primaries, two special schools and 26 nurseries. About 8,900 pupils had an unexpected day off classes.
Further south, Dumfries and Galloway Council . Some schools have also been closed in the and areas.
In North Lanarkshire, all prelim exams for secondary pupils were postponed due to transport problems and all cafes in council leisure and culture buildings were shut.
South Lanarkshire Council closed 18 schools and nurseries throughout the day.
A number of airports were affected by the wintry conditions, with Inverness airport closed during the morning.
Flights in an out of Aberdeen were also disrupted and Glasgow airport was briefly closed while the runway, taxi and passenger routes were cleared.
Police Scotland urged drivers of heavy goods vehicles to exercise extreme caution, and warned they may be asked to park up by officers.
Head of road policing, Ch Supt Stewart Carle, said: “Winter driving is a question of common sense and drivers should ask themselves if they really need to travel when conditions are poor.
“No-one should ever place themselves at risk on the road and it may be worth considering postponing your journey or making alternative arrangements such as delaying travel until conditions improve or using public transport.
“If you are travelling on the roads you should ensure you and your vehicle are adequately prepared for the conditions, making sure you have sufficient fuel and supplies such as warm clothing, food and water in the event you are delayed for several hours.
“Charge your mobile phone and plan your route as well as alternative routes. Listen to media broadcasts, especially local radio, and visit the
Stein Connelly from Traffic Scotland told BBC Radio’s Good Morning Scotland programme: “We’ve experienced some challenging weather conditions through the night and into the morning peak.
“Overnight there were -5.5 degree temperatures [in some areas]. We had 148 gritters out and we are seeing some heavy snowfalls on some of the routes so it’s challenging driving conditions just now.
“This is going to be the same over the next two or three days.”
Traffic Scotland tweeted an image of the early-morning white-out conditions on the M8 at Easterhouse, and assured motorists that gritters were working hard to keep roads open.
Here’s a look at the around Easterhouse from around 15mins ago.
Our pals are on the case and out working hard to keep the roads open, here’s where you can see the gritters in action this morning:
— Traffic Scotland (@trafficscotland)
The Met Office has issued a yellow warning for most of Scotland not covered by the amber alert.
At low levels 2-8cm (1-3 inches) of snow can be expected, but there may also be thundersnow – – especially in western areas.
Forecasters said there was potential disruption to power supplies due to lightning strikes.