Snow is expected to fall over much of the UK and is likely to cause disruption in some areas on Thursday.
The BBC Weather Centre said south-east England and East Anglia could see 4cm of snow, with north-east England and eastern Scotland likely to get 5cm.
The Met Office has issued a severe weather warning across many parts of the UK for Thursday and Friday.
However, the cold snap is expected to pass quickly, with milder weather forecast for Friday and Saturday.
Motorways and other major roads would be treated where freezing temperatures and snow were forecast, the Highways Agency said.
Network Rail said it had snow ploughs, point heaters and staff to patrol tracks on standby, in case of disruption to the UK's railway infrastructure.
The Met Office has forecast most of the snow in southern England for Thursday morning, with about 2cm expected in Hampshire, Lincolnshire, Kent and London.
The snow may settle briefly inland, but not in coastal areas where there is likely to be rain.
ADVICE FOR DRIVERS
Carry warm clothing, food, water, boots, de-icer, torch and spade in your car
Plan your journey before leaving home
Check the weather forecast
Check your route for delays
Source: Highways Agency
Daytime temperatures are unlikely to get above 2C or 3C in these areas and a strong wind could make it feel much colder. Temperatures in Cardiff will be about 3C.
The cold weather is expected to move north during the day.
The north-east of England and east Scotland are set to see the coldest weather in the afternoon and evening, with up to 5cm of snow in some areas and deeper snowfall in the Grampians.
The likelihood of frost and icy roads - coupled with poor visibility - may make driving hazardous in the worst hit areas, particularly on untreated roads.
The Highways Agency has advised drivers to check weather forecasts and road conditions, prepare for their journey and delay travelling if the weather becomes severe.
A Highways Agency spokesman said its winter fleet was on stand-by to treat England's motorways and major A roads, whenever freezing temperatures and snow were forecast.
BBC weather presenter Chris Fawkes said there would be little time for building snowmen, especially in southern England.
"It will turn milder on Thursday night across the South. But snow in eastern Scotland and the North East could settle."
The weekend however would be warmer, with wind and rain, he said.
A Met Office spokesman said: "For many of us this will be the first snow of the winter so there's a novelty factor in that.
"But the amounts aren't going to be terribly high. January and February are the months when we should not be surprised to see snow," he added.
The Met Office's severe weather warnings are an indication to expect disruption and it advises people to take care when travelling, check on elderly neighbours and to keep warm.
Parts of Wales and the Midlands were under snow in November, the first fall this winter.
And last February, there was gridlock on the roads and many schools were closed after heavy snow fell over some parts of England and Wales.