Police and ministers told motorists to stay off the roads across a swathe of central and southern Scotland today after a new amber warning for heavy snow was issued.
The Met Office “be prepared” alert until 10pm could see up to 10cm falling at low levels and 30cm on the highest routes.
Police Scotland said drivers who ventured out in the warning area, which includes the M8, M80, M77 and M74, would face “significant delays”.
That prediction proved correct on several major routes, where vehicles struggling in the slippery conditions brought traffic to a halt.
A lorry crashed through the central reserve on the M74 near junction ten at Wellburn in South Lanarkshire, blocking lanes on both carriageways.
There were also delays further south on the motorway, around junction 13 at Abington.
The M77 was blocked northbound for time near junction six (Kingswell) in East Ayrshire by vehicles in difficulty.
Further south, delays were also reported on the A76 around Mauchline.
Superintendent Louise Blakelock said: “Police are advising not to travel within the amber warning area unless absolutely necessary.
“If you travel on the road network in the warning area, you will be disrupted and you will face significant delays.
“I would like to make it clear there is a high risk of disruption for road journeys and with that comes a high likelihood of the conditions being very poor.
“If you are able to, please make your homeward journey earlier.
“If you are an employer, please think carefully about allowing your staff to return home early if possible.”
The warning area includes the western half of the Central Belt, and south and west of Glasgow as far as Dumfries and Galloway.
Schools in East Ayrshire closed early while all the Kilmarnock-based local authority’s offices shut at 3pm.
The University of the West of Scotland shut down its five campuses at 2:30pm.
Transport minister Humza Yousaf said: “We’re being told the period between 3pm and 10pm tonight is going to be challenging, so I’m urging people to avoid travel within the amber area at that time.
“More widely, we’re advising people to avoid travel if possible.”
The Road Haulage Association urged lorry drivers to stick to the inside lane on motorways.
The Met Office said travel delays were likely and vehicles may become stranded and rural communities cut off.
Its spokeswoman said: “Showers may well be accompanied by hail and lightning at times, increasing the potential for disruption to power supplies.
“Winds will strengthen at times, bringing the potential for temporary blizzard conditions and drifting over hills.”
A yellow - “be aware” - warning for snow covers the rest of Scotland apart from the east coast and Western and Northern Isles until 11:55pm, with up to 7cm expected on lower ground and up to 30cm at higher levels.
A separate yellow warning for ice covers the whole of Scotland apart from the north east from midnight to 10am tomorrow, where up to another 3cm of snow is also forecast.
Other disruption so far today because of the weather included rail passengers being delayed more than an hour on the Glasgow-Oban/Mallaig line at Crianlarich.
More snow is expected to follow on Sunday, with a yellow warning from 6am to 6pm Sunday for 1-15cm to fall over most of inland Scotland south of the Highlands.