A white Christmas is on the cards for much of the UK, with "significant" falls of snow forecast for some parts of the country on 25 December.
Snowfall on Saturday is odds-on for some areas of the UK
Much of Scotland, Wales, Northern Ireland and north-west England were likely to see snow, but falls could happen anywhere, the Met Office said.
Bookmakers were facing a £1m payout and have slashed their odds for snowfall.
But the Met warned the next few days would bring dangerous conditions to the roads, and urged drivers to take care.
It said: "As colder weather sweeps south across the UK through Christmas Eve, snow showers look set to affect many areas during Christmas, with significant falls of snow in some parts of the country."
Philip Eden, a weather expert for BBC Radio Five Live, said: "The forecast indicates that there is likely to be the biggest widespread white Christmas since 1995 when there were blizzards in Scotland and north-west England.
"For a reasonable amount of snow on Christmas Day in the Midlands and southern England, you have to go back to 1981.
"Before that, 1970 was a prominent white Christmas in the South, with even Devon and Cornwall, which normally escape the snow, getting some."
William Hill was quoting odds of 1-4 for snowfall in Glasgow on Saturday, while Ladbrokes were offering 1-6 and said they may soon close the book. It had Manchester at 1-5.
William Hill had Aberdeen at 1-2, with London 12-5 and Cardiff at 11-4. Ladbrokes had cut London's odds from 3-1 to evens, with Cardiff at 2-1.
Ladbrokes spokesman Warren Lush said: "We're shivering at the prospect of a white Christmas across the country. It will cost us alone more than £250,000 and the industry over £1 million.
Don't forget to bring a shovel with you, says the Highways Agency
"What we're most scared of is snow in London. This will cost six figures alone and force us to take a cold bath."
The Met Office warned of treacherous conditions as thousands of people began their festive getaways in the lead-up to Christmas Day.
SOME ROAD HOTSPOTS
M1 northbound J21 (Leics) to J28 (Derbys) - allow extra time for East Midlands airport
M6 northbound J8 (West Mids) to J20 (Cheshire) - allow extra time for Manchester Airport
M5 southbound J14 (South Gloucs) to J20 (Somerset)
M4 westbound J23A to J30 - allow extra time for Fishguard and Pembroke ferry ports
A550 Queensferry (Cheshire) - allow extra time for Holyhead ferry port
It said winds of up to 80mph would batter Scotland late on Wednesday and spread to Northern Ireland, northern England and North Wales on Friday (Christmas Eve).
Snow could also affect some of these areas on Christmas Eve, it said.
The RAC advised people to make basic vehicle checks before setting out in wintry weather.
The Highways Agency recommends drivers take a shovel, warm blanket and warm drink in case they run into problems.