Snow could cover large swathes of the country this week as temperatures plunge, forecasters say.
Up to 6 inches of snow may fall in some areas, with warnings expected to be issued amid fears of travel disruption.
Temperatures could plummet as low as -10C over high grounds in Scotland on Tuesday morning.
Snow, sleet and hail is expected across the country on Tuesday and Wednesday, the Met Office has warned, with 10 to 15cm of snow set to fall in the hills.
Marco Petagna, from the Met Office, told The Independent: “All areas go into a colder, northwesterly air stream for Tuesday and Wednesday.
“Wintry showers could be hail, sleet, snow almost anywhere.”
Two to five centimetres of snow could fall in places more than 150m above sea level, meanwhile 10 to 15cm (up to six inches) of snow could fall in hills above 300m.
A weather warning for ice could also be issued for Tuesday morning as temperatures drop.
In the early hours of Sunday, temperatures fell to -9.5C in Scotland and -6.6C in Suffolk.
Hill snow was expected to fall in Scotland, Northern Ireland and northern England throughout the day.
On Monday, wet and windy weather is set to turn into snow over the hills in Scotland, the Pennines, Welsh mountains and the Peak District, the Met Office said.
Up to 10cm could fall across the high grounds in Scotland, and 5cm across high grounds of Wales and northern England on Monday evening.
Mr Petagna said: “A bit more snow is expected to fall more widely on the hills in the north on Monday night, which may locally fall to some lower levels and we could get some heavier bursts.”
By the end of the week, temperatures are expected to rise to 8C as wintry showers pass.
However, colder weather is expected in the last few days of January into the first half of February with an increasing chance of snow.