Freezing fog is set to descend across the UK after the coldest night in ten months.
Brits saw lows of -10.3C on Saturday night, the chilliest weather since February, the Met Office said.
Sub-zero temperatures are expected again this week, with the mercury expected to dip as low as -8C on Wednesday night.
Met Office forecaster Alex Burkill said: "Temperatures overnight dropped to -7C at Shap in Cumbria. Tonight similar temperatures are expected, dropping to -6C in parts England and Wales.
"Tonight and tomorrow night we are going to see widespread freezing fog, particularly in central, southern and eastern parts of England.
"The weather will require warnings as it will reduce visibility substantially. There will be some really poor visibility on Tuesday and Wednesday morning."
He added that there will likely be snow over the mountains in Scotland today, with wintry showers expected over a wider area at the weekend.
Tonight will bring lingering rain or drizzle in northern Scotland.
The wet conditions should largely clear as the night goes on, though it will remain predominantly cloudy.
Otherwise it will be a dry night night across the UK, with clear spells for many regions, though some mist or fog will form across southern England and Wales.
Patchy low cloud and mist is expected across England and Wales tomorrow.
It will linger throughout the day in places, particularly towards the south where winds will be light, although there will still be some spells of sunshine.
Cloudier and breezier weather is likely in Scotland and Northern Ireland, although it will remain predominantly dry.
Cloud and rain will gradually push into the north-west of the UK on Wednesday.
It will remain largely dry elsewhere, with variable cloud and bright spells.
Wet weather will hit the north and west on Thursday, particularly in north-west Scotland, however it should be dry in the south.
The Environment Agency has issued four flood warnings and 33 less serious flood alerts.
Met Office five-day weather forecast
Today:
Many southern and central areas of Britain, dry and cold with wintry sunshine after frost and isolated fog clears. Northern Britain cloudier, with some rain in northern Scotland where it will turn windier but less cold.
Tonight:
Much of northern Britain cloudy, breezy and frost-free, rain dying out. Central areas dry and cold, southern parts dry and frosty, probably with quite widespread fog developing.
Tuesday:
Southern districts starting frosty and foggy; only a slow improvement, some places perhaps staying misty and very cold. Further north, mostly dry with variable cloud but drizzly in far north.
Outlook for Wednesday to Friday:
Cold with fog for the south on Wednesday, windy with showers in the north. Mild and windy with rain moving south Thursday, clearing Friday to bright or sunny spells.
