Air passengers are being hit with cancellations and delays for a fourth day in the south of England because of heavy fog.
The fog covering the region today, which began to lift as the morning progressed, is causing disruption at major airports, including London Heathrow, where 40 flights were cancelled.
The Met Office fog warning across the south of the country expired at 10am on Saturday, and forecaster Nathan Partridge said he was expecting a "continual gradual improvement" with several patches persisting into the afternoon.
He told the Press Association: "Certainly it's improving, we've got better visibility than we did first thing this morning, and the fog is lifting off the ground so it's now turning into a low cloud issue, which for those out and about driving is obviously an improvement, but still causes some issues in terms of the airports.
40 flights had been cancelled due to air crew and aircraft being out of place following yesterday's disruption
"We will see some fog reforming after dark down in the far south-east corner, south-east of London, this evening for a time, but we will then see the winds picking up which should help to clear that away as well."
Passengers at Gatwick and Heathrow were being warned to expect delays and urged to get in contact with their flight operators for information on disruption.
Heathrow said 40 flights, a mixture of domestic and international, had been cancelled due to air crew and aircraft being out of place following yesterday's disruption.
Gatwick said there were seven arrivals and eight departures with delays of more than 60 minutes at the airport on Saturday.
A spokeswoman said: "Air traffic control restrictions imposed due to heavy fog across the South East and Europe is causing delays to flights to and from Gatwick.
"Passengers are strongly advised to check with their airline as to the status of their flight before travelling if possible. Gatwick is doing all it can to keep passengers moving and we apologise for the unavoidable and unfortunate disruption today."
Stansted Airport said it was expecting a "normal day's operation" with no cancellations, while Manchester Airport said there was no fog affecting flights.
Met office forecaster Mr Partridge said he was expecting the fog to have cleared by New Year's Day, when a band of rain was expected to sweep south across England.
He said: "Although we will be clear of fog there's still a lot of fog across many parts of western Europe, there's huge amounts of it across France, Germany and a few other areas, so that's also a knock-on effect for the flights.
"Although our airports may well get back to normal the other airports will still be affected by it," he warned.
The disruption comes as Public Health England (PHE) warned of an incoming cold snap with temperatures expected to plummet as low as minus 5C (23F) on New Year's Day.
Meanwhile, Highways England said there had been no significant weather-related incidents reported overnight on Friday or on Saturday morning.
A spokesman said: "The events over the last couple of days underline the importance of driving to the conditions.
"Fog can come very quickly so it's important to leave plenty of space.
"The thing that's really important to remember is when it's wet it does take twice as long to stop."
A driver and 16 of his passengers were hurt when a coach veered off an M40 slip road and overturned in heavy fog near Milton Common in Oxfordshire at 2.45am on Friday.
It happened 20 miles (32km) from the scene of a fatal pile-up on the A40 in similarly treacherous conditions on Wednesday morning.
While the fog is expected to clear, a fresh strike by workers on Southern Railway will mean misery for passengers.
Members of the Rail, Maritime and Transport union launched a three-day walkout on Saturday morning in their long-running dispute over the role of conductors.