UP to six inches of snow may fall in Britain this week - with the Met Office predicting a half-term dusting.
A dumping of white stuff is looking likely from Friday, just as kids break for their week-long holiday.
The cold snap is tipped to last until Halloween, with hail and rain blowing in on an an Arctic chill.
Snow could appear on in hilly parts of Scotland towards the end of this week, with temperatures plummeting as low as 6C by the weekend.
The Met Office's long-range weather forecast said temperatures are likely to drop into next week.
And Met Office meteorologist Sarah Kent said there are increasing chance of rural frosts on Thursday as Britain braces for a winter chill.
WINTER CHILL
She said: "If you're out mountaineering don't be surprised if you get wintry weather."
Snow and wintery conditions was likely to hit higher ground in northern areas.
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Cloud, rain and stronger winds are also set to sweep in from the west as Britain braces for a winter chill.
Up to half a foot of snow could fall in Cairngorms in Scotland on Thursday according to WXCharts.
The weather site also forecasts snow across parts of Northern England, including the Pennines and possibly the Yorkshire Dales.
This week's unsettled weather is likely to last until the end of October across the UK.
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."
Bookmakers have already slashed odds on Halloween being one covered in snow, with Coral offering 5-4 on a white Halloween.
Tomorrow could see highs of 20C in London and the South East before the temperatures slumps to 6C by Friday.
RAIN TO HIT
Tonight will be cloudy with some rain or drizzle in the south and east this evening.
The rain is set to clear from eastern areas to allow, but heavy rain is likely to pound western areas overnight.
Tomorrow will see a downpour continue to hit Wales and south West England south and east of England clearing, to allow bright spells and feeling warm.
Rain will become more extensive across Scotland and northern England as the day progresses.
Met Office forecaster Alex Deakin said: "It could turn quite windy across the south on Wednesday.
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"A more significant weather front drives south through Thursday introducing much colder air for the end of this working week,
"So it starts very mild, but it turns an awful lot chillier by Thursday and Friday, with plenty of rain for most of us in between."