The Met Office has issued a fog warning for parts of the East of England.
Forecasters say Central Bedfordshire, Hertfordshire, Luton, Essex, Southend-on-Sea and Thurrock could all be affected.
The fog will begin to come in Sunday evening but is likely to cause most problems overnight and into Monday morning.
The warning is valid until 10.30am on Monday 23 January 2017.
A further Met Office yellow warning has been issued for thick fog across the Anglia region as weather conditions cause delays and cancellations at airports.
Stansted airport in Essex says that heavy fog is affecting flights to and from the airport leading to delays and cancellations. It is advising passengers to check with airlines and allow extra time for journeys to the airport.
Flights into and out of Luton airport are also affected by fog.
The airport says there have been a number of delays to arrivals and departures. Passengers are advised to check in as normal.
The Met Office weather warning is in force until 10am on Saturday 31 December.
The Met Office has issued a yellow weather warning for fog valid until 10am on Friday 30 December 2016
The Met Office says areas of fog and freezing fog have developed, including some dense patches of fog in places.
Driving conditions will be difficult with journeys likely to take longer than usual and delays to air travel are possible.
The Met Office has issued a yellow warning for fog across the East of England from 16:00 Sun 18th December to 10:00 Monday 19th December.
Areas of fog will expand overnight and will be widespread and at times locally dense.
Be aware of hazardous driving conditions, but there may be some improvement by morning as thicker cloud edges in from the east.
Yellow Warning of Fog for East of England covers: Northamptonshire, Rutland, Hertfordshire, Cambridgeshire, Essex, Suffolk, Bedford, Central Bedfordshire, Peterborough & Luton.
The Met Office has issued a yellow weather warning for fog across the Anglia region on Saturday night into Sunday
The warning is valid for all counties from 10pm on Saturday until midday on Sunday
Patches of thick fog will affect central and southern England and South Wales during Saturday night and Sunday morning.
he Met Office is warning people to be aware that low visibility could lead to extended journey times and difficult driving conditions in places.
The Met Office has issued a yellow weather warning for fog across the Anglia region on Saturday night into the early hours of Sunday.
The warning is valid until 6am on Sunday 30 November 2014
The Met Office says: "Patches of fog already forming will become more widespread during the rest of Saturday evening and into the early hours of Sunday with the visibility falling to less than 100 metres in places.
"Later in the night the fog will tend to lift onto hills, before clearing from the northwest as the breeze increases."
This is the visible satellite image of the Anglia region taken at 8.15am on Thursday morning showing the main areas of mist and fog.
Some areas have bright sunny skies and the fog will continue to clear in most areas although it may linger on some coasts.