Temperatures dropped to -13C (8.6F) in Scotland in the early hours of Thursday, making it the coldest night of winter in the UK so far.
The coldest place in the country was Loch Glascarnoch in the Highlands.
The Met Office has upgraded its warning for snow in Wales, south west and south east England, including London, from 14:00 to 21:00 GMT on Thursday, with 3-7cm of snow forecast.
The conditions will bring disruption to Thursday's evening rush hour.
The Met Office warns heavy snow could cause:
- Travel delays on roads which could strand some vehicles and passengers
- Some delays and cancellations to rail travel
- Rural communities could be cut off
- Power cuts are likely and other services, such as mobile phone coverage, could be affected
Snow is forecast overnight into Friday, with totals of up to 15cm (6in) possible in some parts of Wales.
In southern England, there could be 3-7cm (1-3in) of snow.
Southeastern Trains said 21 trains were cancelled or altered on Thursday morning to minimise the impact of ice forming on the rails.
It will run its "winter weather timetable" on Friday - with passengers warned of peak services being busier than normal because of changes to some train times.
England, Wales and Northern Ireland also recorded their lowest temperatures of the winter so far - with Redesdale, Northumberland, falling to -10.4C (13.3F), Sennybridge, Powys, dropping to -9.3C (15.3F) and Magilligan, County Londonderry, falling to -8.5C (16.7F).
❄CONFIRMED ❄— Simon King (@SimonOKing) January 31, 2019
It was the UK's coldest night of the winter so far. In fact, every nation had its coldest night... pic.twitter.com/uFkbCp6OeE
What's the forecast?
BBC weather presenter Simon King said rain, sleet and snow will cause some disruption for Thursday evening's rush hour across the south west of England.
Mid and south Wales will also have snow, and it will move into central and southern parts of England, and into the South East.
The north east of England and north Scotland will also see snow showers and cold temperatures on Thursday night.
Snow and ice caused travel delays and closed hundreds of schools in much of the UK on Wednesday.
In Wales, a climber with a broken leg was airlifted off Snowdon after an avalanche.
Manchester and Liverpool airports closed runways in the morning but reopened them later in the day.
In Devon and Cornwall, police said they dealt with more than 20 collisions and other road incidents in just one hour on Wednesday morning, most of which were in Devon.
In Scotland, the driver of a gritting lorry was taken to hospital after his vehicle overturned.
This temperature comparison tool uses three hourly forecast figures. For more detailed hourly UK forecasts go to BBC Weather.
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