Flights from three London airports were hit by delays after fog shrouded the capital on Thursday morning, Britain's largest airline said.
Festive travel plans faced being thrown into chaos after Heathrow, Gatwick and London City Airport all experienced a raft of hold-ups due to the weather.
A spokesman for Heathrow said some early-morning flights had been been pushed back and knock-on delays could take place throughout the day, adding that there have yet to be any cancellations.
British Airways said on its official Twitter feed that it was aware of fog affecting flights at all three London airports and advised passengers to check their flight status online.
It comes as Britain braced itself for the arrival of Storm Barbara, which is set to batter the country with strong winds.
Scotland is predicted to be the worst hit by the weather, with gusts of up to 90mph forecast in places.
Pockets of Northern Ireland, North Wales and the North of England are also due to feel the force of Barbara, which is due to roll in to the UK by Friday.
The worst of any destruction is expected between Friday evening and Christmas Eve morning, but the potential for structural damage and disruption to some transport services means the storm's impact could be felt long after the winds have subsided.
Met Office spokesman Grahame Madge said: "We are expecting gusts of around 80mph widespread within the amber warning area, up to 90mph in places.
"We have had the good fortune to be able to issue the weather warnings ahead of Storm Barbara coming, with plenty of time hopefully for people to change their plans if they need to.
"But the nature of the storm means it still has the potential to have an impact on power supplies, structures, and disrupt bridge and ferry crossings."
The UK Coastguard issued its own safety warnings ahead of the weekend.
Coastal operations area commander Ross Greenhill said: "We always advise people to check the weather and tidal conditions before they set out so that they can either prepare accordingly or consider whether they should even be going out at all.
"At sea, changes in tidal streams can make conditions worse, particularly if the wind and tide are against each other and tidal heights may hide underwater hazards."
Storm Barbara has been named in line with the Met Office's alphabetical policy for the strongest weather systems and is only the second name designated this season, which began on October 1, after Storm Angus.
British Airways said in a statement on its website: "Fog across parts of southern England is affecting some flights to and from London's airports today.
"For safety reasons, Air Traffic Control has to allow greater space between landing aircraft in fog or during periods of low visibility, and this will mean a reduced number of aircraft being allowed to land each hour.
"We are sorry for the difficulties caused by the poor weather and will do all we can to minimise the effect it has on our operations."