Heavy snow is expected to fall across Wales and southern England later, bringing travel disruption for the evening rush hour.
The Met Office has upgraded a weather warning from yellow to amber for heavy snow between 14:00 to 21:00 GMT.
Meanwhile, temperatures have fallen to the lowest level this winter, with Braemar, Aberdeenshire, dropping to -14.4C (6F) this morning.
It is the lowest in the UK since -15.6C in Holbeach, Lincolnshire, in 2012.
The Met Office warns the 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
What's the forecast?
Further snow is forecast overnight into Friday, with 5-10cm (2-4in) expected in Wales and south west England.
In other parts of southern England, there could be 1-7cm (up to 3in) of snow.