A "snow bomb" could deilver four inches of snow in just a few hours overnight - causing more chaos in the south.
South and east Wales, southern England and the Midlands will see the worst of the flurries, which will fall on top of snow still frozen after several days of cold weather.
The weather front was dubbed a "snow bomb" by forecasters - as it will dump a large amount of snow in a short time, threatening immediate travel chaos.
Temperatures dropped to as low as minus 12.2C last night in eastern and southern parts of England, according to the Met Office, which still has an amber weather warning in place for England.
Almost 40 flights have been cancelled at Heathrow today, the airport said.
The heavy snow and frost have so far claimed the lives of seven people, including a postman who, Royal Mail confirmed last night, died while doing his rounds during the weekend’s freezing temperatures on Exmoor in Somerset.
Julian Mayes, senior forecaster with MeteoGroup, the weather division of the Press Association, said the Rhondda Valley in South Wales has seen 4in of fresh snow already today.
“What is developing is rain along the south coast and South Wales,” he said.
“This will push north into much of central England and Wales tonight. As it does so it will turn to snow. South east Wales may see 5cm-10cm (2in-4in).
“It will persist through much of tomorrow, including along the M4 corridor as far east as Berkshire.
London will see “very little” fresh snow, he added.
Cambridge was the coldest place in the UK last night, reaching minus 12.2C according to Met Office figures.
It was followed by Andrewsfield in Essex (minus 11.1C/12F), Cavendish in Suffolk (minus 10.6C/12.9F), Rothamstead in Hertfordshire (minus 10.4C/13.2F) and Marham in Norfolk (minus 10.3C/13.4F).
The warmest place yesterday was St Mary’s in the Isles of Scilly, which reached 4.7C (40.4F).
Wales, the South West and the West Midlands bore the brunt of the weather overnight.
Several hundred Welsh schools were closed as snow continued to disrupt work and travel across the country.
Large pockets of Cornwall experienced their first snow-based disruption of 2013 today, as many awoke to a thin layer, which closed several schools in remote rural areas.
Icy conditions forced the temporary closure of the northbound A38(M) Aston Expressway, which links Birmingham city centre with the M6, during this morning’s rush-hour.
More than 100 schools were closed in Birmingham, Wolverhampton and Staffordshire.
Tributes were paid today to postman John Bircham, who collapsed as he approached the end of his deliveries in and around the Somerset down of Dulverton on Saturday.
He had been a postman since the late 1980s, Royal Mail confirmed last night.
It is understood that the 57-year-old father of two was towed out of a snowdrift by a farmer before collapsing soon afterwards.