Londoners are waking up to a foggy Monday morning, which is having a big impact on commutes.
Heathrow has cancelled 10% of departures as a precaution with delays expected at all the other airports too.
Drivers are being warned to take extra care on the roads and leave extra time for journeys.
The Met Office weather warning is valid until midday, with fog expected to slowly clear throughout the morning.
The morning is getting off to a fine start with some early sunshine to enjoy.
However, it won't be long before cloud feeds in from the northwest bringing rain and some hill fog later.
An unfortunately grey and damp afternoon is on the cards with further patchy rain.
It will feel humid in the light winds with a top temperature of 20 degrees Celsius (68F).
London City Airport is reporting delays and cancellations of both in and outbound flights.
Martin Stew explains all...
63 flights had to be cancelled at Heathrow Airport this morning due to poor visibility. There were also severe disruptions at London City Airport. Both airports have advised passengers to check with their airlines. There was also no service this morning on the Woolwich ferry.
Heathrow Airport has seen queues of passengers waiting to leave as the freezing fog has led to around 60-70 flights being cancelled.