The first widespread snow of the season is expected as temperatures continue to drop amid freezing fog and gales of up to 50mph.
An 11-day flurry of snowfall has been forecast from Thursday, with the Scottish highlands expected to see the worst of it.
Meanwhile, a yellow weather warning for severe fog remains in place until 8am today in South Wales and southwest England, with the dense mist expected to cause travel disruption.
Chris Fawkes said the murky weather sitting over much of Britain since yesterday will remain initially, because there is currently no wind to move it on.
“We start off with murky weather in the week ahead, but then outbreaks of rain will develop – winds strengthen as the week goes by, it will then turn colder, significantly, through Thursday and Friday,” he said.
A Met Office spokesperson told The Sun: “We could see some snow falling in showers almost anywhere across the UK on Friday and next weekend.”
The national forecaster has warned snowfall “mostly confined to upland regions” is likely by the end of the week, while wintry showers are also expected from Thursday.
And its long-range report predicts further heavy rain, as well as “soft hail, sleet and snow likely” early next week, with “possibly more widespread snow over some hills and mountains”.
Charts show a cold front diving southwards today, bringing rain, but will weaken once it meets incoming high pressure.
And while dense fog slowly moves away, heavy rain will remain in Scotland before pushing down into the rest of the UK.
Temperatures today are expected to sit in the 8-10C range, though lows of 6 degrees are possible in the far north.
“Different weather conditions from place to place on Tuesday,” continued Mr Fawkes as cold air in the east is eventually met by warmer air coming in from the west.
Another cold front will arrive in the middle of the week, however, with winds coming down from polar regions meaning colder temperatures and blustery showers in parts.
Gusts of wind could reach 50mph in western Scotland.
Low pressure moves closer to the UK by Thursday, meaning the “rain is going to be widespread”, continued Mr Fawkes, “at its heaviest, across Wales and southwest England, we could see some localised surface water flooding”.
Showers in Scotland “could start to turn wintry over some of the higher mountains…above three or 400 metres elevation,” he added.
Temperatures are expected to continue to struggle on Friday, averaging 4-6C, with heavy rain likely in parts, while the weekend is also likely to be chilly.
UK 5 day weather forecast
Fog and low cloud in the south clearing, but outbreaks of rain moving southwards. Rain heavy at times over hills in the west, and followed by sunny spells and a few showers into the north later.
Band of rain continuing south followed by clear skies and a widespread frost. Cloudier across Northern Ireland with some drizzle in west.
Cloud and outbreaks of rain across Northern Ireland spreading eastwards to affect western parts of Great Britain through the day. Elsewhere, dry and sunny after a cold and frosty start.
Outlook for Wednesday to Friday:
Unsettled, mostly cloudy and often rather cold. All areas will see spells of rain and some showers, with snowfall mostly confined to upland regions.