Forecasters have warned that the north west and the Western Isles face stormy conditions including rain, sleet and snow.
They also said the weather could worsen for north and western parts of Scotland later in the week and into Christmas Eve, as conditions are expected to deteriorate from Tuesday.
West coast ferry operator CalMac has warned weekend passengers to be aware of possible disruption.
CalMac operations director Drew Collier said: “Weather forecasts for the west of Scotland are predicting a stormy week for many especially as we near the weekend when people will be travelling for Christmas.
“We will review sailings on a case by case basis but would advise anyone planning to travel by ferry to take this into account when planning journeys in the next few days.”
Met Office staff said that, as 25 December approaches, people across the UK should expect wetter and windier conditions, but are unlikely to need a sleigh.
A spokesman for the Met Office said: “It’s relatively a long distance away still, so obviously there’s a fair amount of uncertainty. But it’s looking like it will probably be relatively mild, so unlikely to see much of a white Christmas.”
He said there may be local variations, with the possibility of snow on the mountains in Scotland, and that while overnight temperatures could drop below freezing in some places, it will remain mild during the day.
The Met Office outlook for the next six to 30 days in the UK suggests that Friday will start with local frost and some patchy fog in the south, but it will turn unsettled from the west through the day.
Its website said: “This will herald a changeable and at times very unsettled spell of weather as we move through the Christmas period and towards New Year.
“A succession of deep Atlantic depressions will bring bands of heavy rain east across all parts, although sheltered eastern and south-eastern areas should see some reasonable drier interludes too.
“Winds will often be strong, with periods of gales, and the potential for some stormy conditions at times in the north-west.”