THE Met Office has issued a yellow weather warning for heavy downpours lasting three days.
The forecaster said rain will become persistent across parts of western Scotland during Sunday.
The rain will continue throughout Monday before easing later in the day on Tuesday.
During this period 70-100mm of rain is likely to fall widely, but possibly over 150mm in some exposed hills and mountains.
The yellow warning for rain is in place from 6pm today until 12pm on Tuesday.
Persistent rain will lead to difficult travel conditions and possible flooding in a few places.
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The Met Office said rapid melting of lying snow will contribute to any potential impacts.
A yellow weather warning for wind is also in place today from 12pm to 5pm.
Westerly winds will strengthen during Sunday morning with gusts of 45-55mph expected across parts of Yorkshire during the afternoon.
A few places may experience gusts of up to 65mph.
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Winds will ease into Sunday evening, the forecaster added.
The Met Office posted on X: "Sunday morning starts mild but rather cloudy with some rain in places, especially over western hills.
"Little changes throughout the morning, with perhaps some glimmers of sunshine in the east."
Meteorologist Craig Snell said: "There will be some rain around especially across the hills in the west, but more particularly across parts of Scotland.
"This rain is actually becoming increasingly heavy and persistent as the days goes on, accompanied by a strengthening wind.
"So really leading to quite a miserable end to Sunday here."
Will there be widespread snow this year?
The UK's long range weather forecast suggested snow could be seen on high ground.
The Met Office said it could temporarily also fall at lower levels in the north during any colder interludes.
A picturesque Christmas where widespread snow covers the ground is extremely rare, and since 1960 has only happened four times - in 1981, 1995, 2009 and 2010.
Simon Partridge, a meteorologist for the Met Office, said predicting weather far in advance is like "betting on horses".
He said: "There will be a consensus of the most likely pattern to be coming out but it doesn't always."
At the moment, a picture book Christmas is looking unlikely with "south-westerly winds" expected and rain across the northern and western parts of the UK.
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Everywhere else is expected to be "fairly mild".
However, if you're desperate for snow, Mr Partridge suggests heading to the Scottish mountains - the most likely place for snowfall in the UK this Christmas.
UK 5 day weather forecast
Today:
Many places dry, though rather cloudy. Some rain and drizzle, mainly on western hills, with heavier rain across northern and western Scotland later.
Northeast England and eastern Scotland seeing the best brightness. Mild, though windy with gales in the north.
Tonight:
A mild, but cloudy and windy night in most areas. Some rain in the north and west, heavy across western Scotland.
The clearest breaks developing to the east of hills.
Monday:
Some rain in the north and west, heaviest and most persistent across western Scotland.
Otherwise mostly dry with some bright spells. Another widely mild, though rather windy day.
Outlook for Tuesday to Thursday:
Rain spreading from the southwest during Tuesday. Further rain on Wednesday England and Wales.
Showery elsewhere. Generally brighter and showery on Thursday. Often windy. Briefly very mild, then colder later.