The Meteorological Office is warning that temperatures are expected to drop to below minus 8ºC by the middle of the week, with a warning of heavy snow in Scotland.
Winds are expected to shift from the east to the north bringing an Arctic chill and below-average temperatures for the time of year.
A yellow warning is in place on Wednesday for snow, which the Met Office is advising could cause disruption to road, bus and train journeys.
“At the moment we have an easterly flow and as such our winds are coming from the east and that is a cold direction," said Alex Burkill, Met Office meteorologist.
"However, from Tuesday onwards we are going to get a northerly flow, so our winds coming from the north, that is Arctic air leading to our temperatures dropping even further as we go through this week.
“It’s going to turn even colder and feel even colder still with temperatures well below average for the time of year, both by day and by night.”
He said temperatures overnight on Wednesday into Thursday would drop to minus 7ºC or minus 8ºC — or even colder.
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“It looks like the cold is going to be very widespread," Mr Burkill said.
"Perhaps Northern Ireland and East Anglia won’t be that cold, maybe just a degree or two below freezing, otherwise we are talking about several degrees below freezing across Scotland, Wales.
“Much of England, including the south-west, we could see temperatures of minus 5ºC or minus 6ºC, which is exceptionally cold.
“We have a snow warning across the northern half of Scotland for Wednesday and that is when the snow showers coming from the north will be most impactful.
"They will probably start on Tuesday and we will see very significant snow in the north. It looks like it could last a week.
"The northerly flow is going to stay with us. It’s not going to be particularly unsettled, so there will be some showers. It’s mostly going to be largely dry but cold.
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“From the middle of next week there are some signs we may see some more unsettled weather with milder weather coming up from the south, but it’s far away at the moment.
“At the moment it is cloudy, meaning there won’t be huge differences between daily highs and overnight lows, but as we go through this week, we will get that cold northerly flow with clearer skies, so sunny and crisp by day but even colder at night.”
Mr Burkill said temperatures dropped to minus 3.8ºC at Drumnadrochit near Inverness on Saturday night.
But temperatures should remain at about minus 2ºC at night time in Scotland for the next couple of days and a few degrees above freezing for the rest of the country until the cold snap arrives on Wednesday.
Temperatures in the day time should be about 8ºC or 9ºC, dropping to 5ºC or 6ºC as the week progresses.