Arctic air is set to hit most of the UK this week, bringing chilly winds and the threat of snow.
The week will begin unsettled but relatively mild with temperatures set to fall on Thursday as biting northerly winds make it feel bitterly cold.
The cold snap is set to last through the weekend and into the early part of next week.
Daytime temperatures will struggle to get above freezing and the wind chill factor will make it feel sub-zero.
Met Office forecasters have warned that the Arctic blast is likely to bring snow showers to many parts of the country.
Friday the 13th will be the coldest day of winter so far - with the entire country expected to be blanketed in up to four inches or 10 centimetres of snow.
From Friday the whole of the country could see freezing storms bring two to four inches (5 to 10cm) of snow as temperatures dip "well below" freezing.
Temperatures could drop as low as minus two degrees Celsius - 28 Fahrenheit on Friday night but daytime temperatures not much higher - but the Arctic blast will make it feel a lot colder.
The Met Office has warned commuters to expect heavy traffic problems as thick ice and snow are likely to disrupt services across the country on Friday.
Forecaster Marco Petagna said: "We could see the coldest day of winter on Friday.
"A cold front moving in from the Atlantic will bring heavy frost and frequent snowstorms.
"It is likely that five to ten centimetres of snow will come in from the north and fall as far as the south of the country on Friday, and there could be even thicker snow in the hills.
"Daytime temperatures on Wednesday will be around four to six degrees C (39 to 43 F) but harsh winds will make it feel as if temperatures are well below freezing.
"Temperatures will become increasingly colder throughout the week and by Friday it is likely that nighttime temperatures will be as low as minus 2C (28F)."