The Met Office has warned of a three-day washout with up to six inches of rain expected on higher ground.
Three consecutive yellow alerts have been issued for 42 hours of downpours from 6pm on Sunday until noon on Tuesday in north-west Scotland.
In areas where snow has fallen, residents are being warned a rapid thaw will contribute to the risk of homes and businesses being flooded.
The country has experienced almost a week of benign conditions ranging from sunshine and freezing temperatures in the north to gloomy and stubborn fog in the central belt, with temperatures plunging below 0C and as low as -11C.
But a striking change is imminent, thanks to a large area of low pressure rotating over France and the near continent.
Aiden McGivern of the Met Office said: ‘The next area of high pressure builds into the south but it’s going to be sufficiently far south to allow westerlies across much of the UK.
‘That means increasingly wet weather across northern areas, especially western Scotland, with some significant rain totals totting up from Sunday for a few days.
‘We are also going to see strong winds for the north east of the UK.
‘Anticyclonic gloom’, a phenomenon that occurs when high pressure traps moisture near the Earth’s surface resulting in cloudy and dull weather, is seen over St Ives, Cambridgeshire
A striking change in UK weather is imminent, thanks to a large area of low pressure rotating over France and the near continent. Pictured: Gloom over St Ives this morning
A map showing current flood alerts in place across England ahead of expected heavy rain
‘It’s also going to turn much, much milder.’
The yellow ‘be aware’ warnings affect the north west of the country, including Central, Tayside and Fife, Highlands and Islands and Argyll and Bute.
The warning states: ‘Rain will become persistent across parts of western Scotland during Sunday, continuing throughout Monday before easing later on Tuesday.
‘Around 70mm to 100mm of rain (up to 4ins is likely to fall widely during this period, but possibly over 150mm (6in) for some exposed hills and mountains.
‘Rapid melting of lying snow will also contribute to any potential impacts.’
People have been told to expect flooding of property, possible power cuts and longer journey times.
Driving conditions could be severely impaired, with spray and road flooding making journey times longer.
While the main areas of population lie out with the warning zones, the likes of Glasgow can also expect a very soggy Sunday and start to the working week.
The Met Office has issued yellow weather warnings for north-west Scotland from Sunday
This weekend, milder air coming in from the west will see things warm up considerably, going from 4C (39F) on Saturday to 11C (52F) on Sunday.
However, this will be accompanied by heavy rain which could persist for several days.
Grahame Madge, of the Met Office, explained: ‘The warning area has been carefully created to encompass the areas likely to see the highest rainfall totals and impacts.
‘Other parts of Scotland are expected to see rain during the period, but not to the levels of the warning area.’
Although the current warning expires on Tuesday, forecasters are watching another system that could bring more misery and further alerts on Wednesday.
This is the second-last shopping weekend before Christmas. The run-up to the festive period has been a wash-out for the retail trade, which relies on November and December for a significant proportion of their annual turnover.
The period November 23 to 24 was badly affected by Storm Bert and last weekend saw the impacts of Storm Darragh, when people living in affected areas were warned not to travel.
Road operator Bear Scotland said it would have spotters in place from Sunday at the Rest and Be Thankful in Argyll in case heavy rain leads to movement on the mountain above.
On Friday, the Scottish Government said it was committed to finding a long-term solution to the landslide danger affecting this part of the A83 by promising further improvements and public consultation beginning in the New Year.
