A second amber alert, for heavy snow, covers an area to the north from 9am to 8am tomorrow, for 5-20cm, and up to 40cm over higher ground.
Lesser yellow warnings for snow and ice cover most of the rest of Scotland, with a separate yellow warning for winds gusting up to 70mph in Orkney and Shetland.
Met Office chief meteorologist Will Lang said: “Saturday’s weather brings a range of winter hazards with very dangerous travelling conditions likely in some places. Freezing rain forms when rain freezes on impact as it hits a cold surface – it is quite rare in the UK and when it does occur, the impacts can be severe.
“Many will know it as black ice, and the danger is it forms quickly, is difficult to see and is incredibly slippery.”
Superintendent Louise Blakelock, deputy head of road policing for Police Scotland, said: “I appreciate many people will be planning Christmas shopping trips and have festive social events planned. “However, if you do travel, you are likely to experience significant delays.
“Drivers of goods vehicles and buses should drive with extreme caution and be aware you may be requested to park at a suitable position by the police.”
Transport secretary Michael Matheson said: “This is the first significant weather warning of the Christmas period, and we are likely to see dangerous travelling conditions.”
Edinburgh City Council transport convener Lesley Macinnes urged people to be “extremely careful”.
She said: “We make every effort to keep roads and pavements clear of ice but rain can sometimes wash salt away and subsequently freeze. We will work to re-treat these areas as quickly as we can.”
A Glasgow City Council spokesman said: “Freezing rain will almost certainly create highly challenging conditions for all road users. We advise people to exercise the greatest possible caution.”
Network Rail drafted in snowploughs from England, according to sources.
CalMac has cancelled ferries on routes including to Coll, Tiree, Islay, Colonsay, Gigha, Iona and Rum today.
Loganair passengers can postpone their flights free.