Plunging temperatures are expected across the country this weekend with the mercury predicted to dip as low as -6C (21.2F).
Forecasters said most areas will remain dry and bright with temperatures between 5C (41F) and 8C (46.4F) during the day on Saturday and Sunday.
But things are looking much colder as the night draws in.
Met Office forecaster Mark Wilson said: “The South West of England could see -2C (28.4F) locally on Saturday (evening) while the West and East Midlands will experience temperatures as low as -3C (26.6F).
“For the rest of the UK temperatures will be around -5C (23F) to -6 (21.2F) in the evenings on Saturday and Sunday.”
Beyond the weekend things will become “increasingly cloudy and milder from the North West”, he added.
A cold weather alert was issued by Public Health England (PHE) from 6pm on Sunday to 6pm on Tuesday and the organisation is urging people to prepare for cold weather conditions and look out for those most at risk.
Dr Owen Landeg, principal environmental public health scientist at PHE, said: “Below 18 degrees, changes to the body mean that the risk of strokes, heart attacks and chest infections increase so heating homes to this temperature is particularly important to stay well.”
Wilson said that northern and western Scotland will see brief showers on Saturday morning before sunnier conditions on Monday morning with temperatures of around 11C (51.8F).
The top temperatures in south-east England and the West and East Midlands will be around 8C (46.4F) on Monday, he said.
The cold snap comes after Storm Brendan swept across parts of the UK last weekend causing road closures and rail disruption, as well as gales of up to 80mph.
It also marks a change from last month when meteorologists confirmed that a new UK maximum temperature record for late December was set in the Highlands.
A temperature of 18.7C (65.66F) was recorded at Achfary in Sutherland on December 28.
The reading was validated following a “rigorous verification process”, the Met Office said.
Asked why temperatures have dropped, Wilson said: “It’s all to do with the pressure pattern and it also depends on how high or low the pressure is. Right now there is cold air sitting directly on top of the UK and there is high pressure coming from the north and the east.”