Britain is bracing itself for an icy blast over the coming week when temperatures will plummet below freezing to bring snow and widespread frosts.
The chill weather - the first wintry spell for many - will be a sharp change from the mild weather last month, the wettest on record and the warmest ever December, when temperatures averaged 7.9C (46.2F).
Forecasters are predicting a wet start to the week, with wintry showers especially on high ground, before an area of high pressure towards the weekend will see temperatures struggling to reach 5C (41F) in the South and not rising above freezing further north.
Motorists, pedestrians and cyclists are being warned of the risk of frost and ice on roads.
There are also forecasts of rain, and the Environment Agency still has more than 150 flood alerts and warnings in place across England and Wales following the devastating Christmas and New Year floods.
The Met Office issued severe weather warnings overnight on Sunday for rain along much England's south coast and the South East, where there will be heavy showers, hail and thunder. Up to 1.2in (30mm) may fall by this morning, forecasters warned.
Mel Harrowsmith, head of civil contingencies at the Met Office, said: "For many the weather during the coming week is likely to be the first experience of winter, with either frost, wintry showers or even snow affecting many areas of the UK."
During the early part of the week cold air will spread southwards, bringing the chance of frost, ice and, for some, the possibility of sleet, snow and hail, the Met Office said. Daytime temperatures are likely to be in the range of freezing to 5C (41F).
Southern Scotland and parts of north-east England, particularly the high ground over the Pennines, received a dusting of snow over the weekend and Billy Payne, a forecaster with MeteoGroup, said more was likely in the coming days.
He said: "We are still going to have some outbreaks of rain and mainly hill snow for Scotland, particularly in the south. It will be cold in northern Britain, between 4C (39.2F) and 7C (44.6F), and around 6C (42.8F) to 9C (48.2F) in the South."
Today and Tuesday will see "messy" weather.
Mr Payne said: "An area of low pressure will bring rain and showers, with a chance of anyone seeing rain or showers, particularly in the East during the morning, and in more northern and western parts throughout the day.
"There could be some snow over northern England during the morning, mainly on high ground again.
"It will be colder in the North, around 3C (37.4F) to 6C (42.8F), and 6C (42.8F) to 9C (48.2F) in the South, not far off normal for this time of year, but compared to December's weather it will certainly be feeling a lot colder."
Low pressure on Tuesday and Wednesday will move away to the East, and chill north-westerly winds will cause temperatures to drop off, with wintry showers on both days.
On Wednesday temperatures will peak at 7C (44.6F) in the South and 5C (41F) in the North, but on higher ground in Scotland it will struggle to reach above freezing, Mr Payne said.
He added: "On Wednesday and Thursday there could be an area of low pressure coming in from the North West, bringing the potential for longer spells of rain, sleet and snow more widely, even across England and Wales.
"The end of the week may be a bit drier as an area of high pressure comes in, but temperatures will drop to 2C (35.6F) to 5C (41F) in the South and not rise above freezing further north, with widespread frosts overnight across the whole of the UK."
Looking ahead, the third week of January is likely to see weather becoming slightly milder as Atlantic weather systems try to push across the country, bringing rain and strong winds.