Snow riding on an Arctic chill will blast the UK before the end of the week, forecasters say.
The cold snap is expected to hit parts of the country within days after experts predicted plunging temperatures caused by a polar vortex.
Snow could appear on mountain tops across Scotland on Thursday, with a cold snap sending mercury levels as low as 6C by the weekend.
John Hammond, former BBC weatherman and meteorologist for Weathertrending, said: "After a very mild few days, much colder air will arrive from the north later this week, which may bring some snow to the Scottish mountains.
"That cold spell may not last all that long, but frost, and eventually snow, will probably figure more frequently in our forecasts before too long."
Met Office meteorologist Sarah Kent said there are increasing chance of rural frosts on Thursday.
"If you’re out mountaineering, don’t be surprised if you get wintry weather,” she said.
Temperatures are set to drop dramatically nationwide, as an 18C high on Tuesday plunges to just 6C by Friday.
The mercury will struggle to get out of single figures for much of the rest of the week.
Before the icy chill Brits will enjoy warmer conditions on Monday and Tuesday, if not always pleasant.
Heavy rain is expected in the east and the west of the country today, with more to come for the south and west on Tuesday.
The Met Office forecast for Wednesday and Thursday predicts longer spells of rain accompanied by windy coastal gales.
By Friday the UK will be drier and less windy but showers will still hit some areas.
This cold snap has been delivered by low pressure at the surface moving northeasterly creating a Northern wind flow .
This weather will likely to persist towards the end of October across the UK, the Met Office says on its long-range forecast.
Any additional cold periods will be short lived and focused in the north, it says.
MET OFFICE OUTLOOK
Today:
Some early fog in southeastern areas of England, then brighter for a time. Elsewhere mostly cloudy. Rain in the west spreading east, perhaps heavy in places. Brighter across parts of Northern Ireland later. Mild everywhere, warm in any brighter spells.
Tonight:
Rain easing but still patchy drizzle. Heavier rain may skirt the south coast and returns to the west later. Hill fog affecting some areas. Very mild but rather breezy.
Tuesday:
Some southeastern areas of England mainly dry, with some bright and warm spells. Many other areas cloudy with areas of rain, some heavy, moving northeast. Breezy and very mild.
Outlook for Wednesday to Friday:
Showers or longer spells of rain on Wednesday and Thursday. Often windy with coastal gales. Turning drier and less windy into Friday but still showery for some and noticeably colder.
