Bookies have cut the odds on a white Christmas while freezing temperatures could bring the chilliest night of the autumn so far.
Ladbrokes now make it 4/5 that snow falls on Christmas Day, with Aberdeen the favoured city with odds of 7/4, or there is a 5/1 chance of London becoming a winter wonderland.
Hats and scarves will be needed before the festive season as forecasters warn that the mercury could plunge to as low as minus 7C (19.4F) in parts of Scotland on Sunday night.
Met Office forecaster Marco Petagna said: "Tonight could be the coldest night of the autumn so far."
He said the coldest temperature of the autumn was on November 6 in Braemar, Aberdeenshire, when the mercury fell to minus 6C (21.2F).
"Tonight we could get down to minus 7C in the Scottish glens, and possibly even minus 6C locally across places like Katesbridge in Northern Ireland, and perhaps higher ground of Cumbria, places like Shap in Cumbria," he said.
He said it would become less cold over the next few days but would turn chilly again, with frost expected in some places from Friday night onwards.
Mr Petagna said it was too early to tell whether or not a white Christmas was on the cards, but bookies said they have taken a flurry of bets.
Coral's John Hill said: "We've taken an avalanche of bets on this year being a white Christmas as punters are convinced that everybody's dream will become a reality with snowfall in mainland UK on Christmas Day.
"We've not seen a gamble this early on there being a white Christmas for many years, therefore we'll be keeping our fingers crossed that temperatures don't continue falling over the next six weeks otherwise it won't just be Santa handing out presents this Christmas."
Jessica Bridge of Ladbrokes said: "The odds are falling as quick as the mercury and it looks like the bitter weather is here to stay."