WIDESPREAD disruption to transport networks across central and northern Scotland is expected today after snowfall of up to 15cm (6in) was predicted.
Transport Minister Keith Brown said the morning rush- hour would present the "biggest challenge of the winter to date" with delays expected on roads and rail services.
The M8 east of Glasgow and inland areas of eastern Scotland are at the highest risk of disruption as snow falls on patches of dense ice that formed earlier this week, Mr Brown warned.
The Met Office updated its warning to amber – meaning "be prepared" – covering the Highlands and Islands, Central Tayside, Fife, Strathclyde and Grampian regions as temperatures were due to drop to -6˚C.
It follows snowfall earlier this week which has already caused disruption to flights, motorists and public transport users.
The Scottish Government's Multi Agency Response Team is due to be operational and the Glasgow-based national Traffic Control Centre will monitor the situation, Mr Brown said.
"So far this week the network and the public have coped well with some testing conditions, however this severe weather warning suggests we face the biggest challenge of the winter to date," he added.
"The Scottish Government's resilience team is monitoring the situation as it develops to deliver a co-ordinated response.
"Ministers are being updated on preparations as the situation evolves, and daily conference calls have been taking place between key responders."
A spokeswoman for Aberdeen Airport said most services had been subjected to "considerable delays" yesterday due to snowfall in the north-east.
Ice and snow closed a number of roads yesterday, including the B974 Fettercairn to Banchory road and the A821 Duke's Pass between Aberfoyle and Brig O'Turk.
Anthony Astbury, chief forecaster at the Met Office, said there would be "treacherous" conditions this morning after an overnight drop in temperatures to -6˚C in some areas.
He said sleet and snow would spread from the west, with 10cm to 15cm of snow likely to fall above 400m (1300ft), with 5cm to 10cm above 200m. At lower levels 2cm to 3cm of snow is likely before turning back to rain.
Mr Astbury added: "Despite turning to rain, the lying snow and ice will struggle to melt and this will bring some treacherous conditions."
David Simpson, route managing director in Scotland for Network Rail, said it had invested in "robust" resilience measures and would be deploying rapid response teams to deal with any disruption.
"We've invested heavily in innovative technology such as NASA-grade insulation to prevent points freezing and snow displacers which prevent snow building up. This will make the network as robust as possible and help us to keep Scotland moving," he said.
The Multi Agency Response Team, based in Glasgow, includes representatives from Traffic Scotland, Transport Scotland, the police, rail operators, road operating companies and the Met Office.