Emergency response teams say they are prepared for predictions of up to 30cm, with drivers being urged to take care in the treacherous conditions.
Worst affected is likely to be the Highlands, Aberdeenshire and the south-west of Scotland in the most widespread snowfall for three years, the Met Office said.
The coldest areas are likely to be Aboyne and Braemar, where it is expected to be -7.1C today with much of Scotland getting some snow, although the wind-chill factor will make it seem even colder.
The Lothians and Scottish Borders will also be badly hit and Strathclyde, Central and Tayside areas all have yellow alerts in place from Friday over the weekend, with drivers being told to "be aware" of snow and ice.
Parents are also being warned to check whether schools are open when the snow comes.
Met Office spokesman Daniel Williams said: "On Friday and into Saturday morning, we expect to see some snowfall across Scotland – with 2cm-5cm falling quite widely, but parts of the Highlands and western parts of Aberdeenshire could see 10cm-15cm, or 20cm-plus on high ground. I'd say it's possible 30cm may fall on high ground in the Highlands. Bear in mind that with the wind blowing too, there may be snow drifts to contend with also. It's probably accurate to say this is the most widespread snowfall since December 2010.
"A key message from the Met Office is that people should keep up to date with the forecasts and weather warnings over the next couple of days, and certainly on Friday they should check local transport information and any other local advice – parents should check if schools are open – before heading out on Friday and Saturday. People should be prepared to change their plans."
Neil Greig, of the Institute of Advanced Motorists, said: "Carry a basic survival kit in the car. Extra clothes, a blanket, winter footwear and some food and water may be very useful if you get caught in tailbacks or unexpected road closures."
A Transport Scotland spokesman said preparations were under way. He said: "Local authorities and operating companies have more salt in stock or on order than ever before, additional gritters and specialist equipment are available, and new weather stations and cameras are helping to improve decision making and deliver better informed communications However, the public should stay vigilant and listen to local radio reports and travel updates, and motorists should heed police advice and drive to the conditions."
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