Forecasters are predicting a widespread frost across the UK, with the potential for -10C (14F) in some places.
Most areas will turn dry on Monday evening and, as skies clear, temperatures are set to plummet overnight.
“Rural areas, mainly in Scotland, could dip as low as -10C (14F), while -6C (21F) is possible in parts of Northern Ireland and north Wales,” said Sky News weather producer Chris England.
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“Some of the lowest temperatures are likely to be in those valleys sheltered from the northerly wind,” he added.
On Tuesday, England and Wales look mostly fine, although western parts will see a little rain later.
Meanwhile, Scotland and Northern Ireland will see afternoon rain, with a spell of snow likely as the rain moves into the cold air.
“The snow risk looks likely to be confined to the higher ground – above 400m – and restricted to Scottish hills perhaps the northern Pennines,” he said.
“But the timing is uncertain and the forecast is for rain generally at lower levels, so we’re not expecting much impact.”
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The predicted freezing conditions are in stark contrast with temperatures recorded over the weekend.
At one point it reached 16.4C (61.5F) in Cardiff as winds brought milder air from the South and South West.
“That’s about five degrees above average – it should be about 10-12C that time of year,” said Met Office meteorologist Marco Petagna.
He added there is a chance temperatures could drop again this weekend as northerly winds are expected to develop.