The Met Office has issued a severe weather warning for thick fog in parts of England and Wales.
The yellow warning begins at around 5pm on Sunday and lasts until 8am on Monday.
The thick fog is expected to engulf Cardiff and the city’s surround areas in the south of Wales.
The entire counties of Cornwall and Devon, parts of Somerset and Wiltshire and a section of Oxfordshire have also been issued with the yellow warning.
The warning also extends to the South East of England including London, and there thick fog has been forecast for the Midlands too.
The thick fog is expected to affect flights with the Met Office warning of possible delays and even cancellations.
Public transport could also be interrupted with slower journey times for buses and trains.
The Met has also warned that it will get colder across the country as the week goes on and winter gets underway.
Temperatures will average just 3C or 4C every day and by the end of the week they will drop to as low as 0C in central Scotland.
More miserable rain will bring gloomy conditions to the north on Monday and the wet weather will continue throughout the week, amid lower than average temperatures for this time of year.
Brits will need to wrap up warm elsewhere on Friday too, with the mercury hitting lows of 2C in eastern parts of Wales, 3C in the Midlands and 2C-3C in the north of England.
The Met Office’s long range forecast says: “Temperatures may start off near normal, though often feeling colder in windier and wetter spells.
“Below normal temperatures are then slightly more likely for later in the period.”