The Met Office has issued a severe weather warning of more heavy snow and icy roads for south and mid Wales.
Police were warning motorists to stay home unless their journeys were absolutely necessary. Major roads including the Heads of the Valleys in south Wales became gridlocked, causing long delays and tailbacks as commuters tried to make their way home early.
Some towns and villages were cut off by impassable roads, and bus services in several areas were stopped.
The driver of an ambulance had a lucky escape when his vehicle skidded and overturned near Llanarth in Ceredigion, closing the A487 for several hours.
Snow only began to fall in the south east of the country after lunchtime on Thursday - the area's first taste of what the rest of the country woke up to.
And it is not likely to subside for a while as the Met Office said: "Heavy snow showers this afternoon and evening will lead to some significant accumulations of snow, particularly over high ground and in areas exposed to the strong and gusty northwesterly winds.
There were idyllic scenes, but chaos, too
"There will be localised drifting and blizzard conditions in upland areas. Roads are likely to become icy in areas affected by the snow, giving some dangerous driving conditions, and motorists are advised to avoid driving in upland areas if possible."
More than 350 schools throughout Wales were closed by mid afternoon on Thursday, while homes and businesses lost power and telephone connections.
Many were expected to remain closed on Friday, and parents were urged to check with individual schools for the latest information.
Up to six inches of snow lay on some roads and eight inches on the hills. Gritters and snowploughs were expecting to be out all night in areas including Carmarthenshire and Swansea.
Snow ploughs had earlier been out in force to keep the main routes open, but many minor roads remained impassable, made worse by a number of minor accidents.
In Ceredigion - where snow rarely sticks and causes problems - the sudden flurries caught drivers unawares.
"The snow fell in Aberystwyth at about lunchtime," said Gareth Roberts, from Ceredigion County Council.
"A lot of businesses decided that it was probably better for the workers to go home, and then everybody rushed home at the same time," he added.
"Although all the roads had been gritted, everybody was following everybody else, and causing gridlock."
Some council are drafting in extra resources to minimise disruption services with highways teams working throughout the night gritting main roads and salting pavements.
A few hospitals have also been affected with outpatient clinics being cancelled at Ysbyty Gwynedd in Bangor and Llandudno General Hospital.