Forecasters have warned that the meteorological event - dubbed the ‘Beast from the East’ - has disturbed the jet stream, allowing chilly winds from Siberia to blast the UK - and could last well into March.
The mercury is expected to go as low as -2C in Glasgow and Edinburgh on Monday 26 February.
Temperatures during the early part of the week reached 2-4C above normal for the time of year but a colder, drier trend is expected to take charge lasting through to the end of the month and well into March.
Met Office spokesman Oli Claydon said temperatures will “slowly ramp down through the week”.
Describing sudden stratospheric warming, he said it was caused by a huge rise in air temperature in an area around 18 miles (30 km) above the North Pole.
“There is a very big, very cold pool of air that circulates around the North Pole - sudden stratospheric warming, as it says on the tin, is when the stratosphere suddenly warms,” he said.
“Last week we saw that take place - a sudden jump of around 50C - so that can disturb the way that cold pool of air moves around the North Pole very high up.
“That can lead in around 70 per cent of instances to it impacting the drivers that affect our weather in northern Europe as well.
“So what we are seeing in this case is it disturbing the jet stream and weakening the jet stream.”
Mr Claydon said sudden stratospheric warming and its impact on British weather is “not a yearly occurrence but is not unheard of”, and last impacted the UK in 2013 and 2009.
“These colder conditions are expected to last into next week and could be fairly prolonged, and could still be with us into the beginning of March,” he said.
The Met Office also said there could be some frosty nights, and warned that into next week even colder air from Russia could move across the country.