Snow and ice is forecast for large parts of the UK this weekend as a cold snap dubbed the “mini beast from the east” arrives.
About 70 flights to or from Heathrow have been cancelled and drivers are advised to prepare before setting out.
Met Office Yellow “be aware” warnings are in place for Saturday and Sunday.
Amber warnings of a possible risk to life affect north west England, Yorkshire, the Midlands, London and south-east England from the afternoon.
The Met Office says snow showers are expected to become more frequent between 16:00 GMT on Saturday and 09:00 on Sunday.
Amber warnings are also in place for south Wales and south-west England between 00:05 and 18:00 GMT on Sunday.
“Travel delays on roads are likely, stranding some vehicles and passengers. Some delays and cancellations to rail and air travel are likely,” the Met Office says.
On Saturday 1-3cm of snow is expected across large parts of the UK, while 5-10cm could fall in the areas with amber warnings and up to 15cm on hills.
Temperatures are likely to drop to around freezing and gusts of up to 70mph are expected in northern England and parts of Wales.
The low temperatures will continue into the start of the week but are expected to be back around average from Tuesday.
The affected Heathrow flights are mostly on short-haul routes, although BA services to New York and Chicago have been disrupted.
A BA spokesman said: “During cold weather conditions aircraft have to be de-iced prior to departure to ensure that they are safe and additional measures are taken to ensure the safety of our operation is maintained at all times.”
Other cancelled flights from Heathrow include services from Lufthansa, Aer Lingus, TAP Air Portugal and KLM.
However, the airport said it does not expect significant disruption.
Some trans-Pennine roads are expected to be “severely affected” in the early hours of Saturday.
Highways England’s Head of Road Safety, Richard Leonard, said: “Our gritter drivers will be out treating our roads around the clock but it is still important to drive to the conditions when snow is forecast.
“Drivers should plan their journeys, monitor weather reports and pack a snow kit of blankets, food, water and a shovel if they really need to travel.”
Network Rail is running empty trains to help keep the network clear of snow.
A cold spell nicknamed “the Beast from the East” saw much of the UK and Europe blanketed in snow at the start the month.