Heavy snow blizzards, "biting" winds, and significant travel disruption are predicted in the UK as Storm Emma moves into the south of the country.
Meanwhile the "Beast from the East" front continues to freeze Scotland and the north, with up to 40cm of snow expected in some places.
A red warning for snow – meaning there is a potential risk to life – is in place in Scotland until 10:00 GMT.
An amber warning for Scotland and northern England will last until 18:00.
A further amber warning for snow and ice will be in place for London and the south east, south-west England, Wales and the West Midlands from midday until 08:00 on Friday.
The Met Office said there were signs the cold easterly flow was likely to last into next week and possibly into the following week.
By Thursday morning, parts of England and Wales may see widespread snow associated with Storm Emma, said Andy Page, of the Met Office,
"Parts of south west England and Wales could also see freezing rain for a time on Thursday night – a relatively rare weather phenomena in the UK," he said.
BBC Weather's Ben Rich predicted "blizzard conditions" by Thursday evening across the south west of England, Wales and parts of the Midlands.
He said a "biting easterly wind" will make it feel like -11C (12F) in Birmingham and Cardiff – on what is the first day of meteorological spring.
The Met Office said some areas of Scotland could see up to 30cm (11.8 inches) of snow fall and possibly up to 40cm (15.7 inches) in "a few places" by mid-morning.
Up to 10cm (7.8 inches) is forecast to fall in parts of Scotland and northern England, with up to 40cm over the hills.
There is potential for up to 50cm (19.6 inches) over parts of Dartmoor and Exmoor, the Met Office added, with up to 20cm (7.8 inches) falling in southern England, Wales and the West Midlands.
Rail passengers have been warned to avoid travelling to or from Scotland on Thursday while in Kent 50 stations will be closed.
Almost all train operators are expected to be affected by conditions.
Several are planning to run amended timetables, with passengers being urged to check before they travel.
Glasgow Airport has said there will be no incoming or outbound flights until 11:00.
Traffic on the M80 between Glasgow and Stirling was brought to a standstill for several hours on Wednesday and overnight into Thursday, as emergency services dealt with a series of accidents.
In the early hours of Thursday, drivers reported still being stuck on the M80, which is closed in both directions between Junction 8 and Junction 9, and on the M876, which is closed to northbound traffic after Junction 1.
Those stuck in their cars told of people handing out food and extra blankets to those who were stranded overnight.
Hundreds of schools will be closed across the UK. Schools in some areas of Wales will not reopen until Monday.
On Wednesday, severe snow caused the cancellation of flights. Trains and traffic ground to a halt on major roads.
The worst hit areas were central Scotland – where a red alert for snow is now in place – as well as Kent, East Anglia and the North East of England.
In London, a man died after being pulled from a frozen lake.
How has the cold weather affected you? Share your pictures, video and experiences by emailing [email protected].
Please include a contact number if you are willing to speak to a BBC journalist. You can also contact us in the following ways:
- WhatsApp: +447555 173285
- Tweet: @BBC_HaveYourSay
- Send pictures/video to [email protected]
- Upload your pictures/video here
- Send an SMS or MMS to 61124 or +44 7624 800 100