There may be poor visibility in some areas. Some patches of fog will form and also some frost.
Radiation fog occurs mainly in the winter, during clear skies and calm weather conditions.
Nearly the whole of Northern Ireland, and the west of England, including Liverpool, Manchester, Wolverhampton, Bristol and parts of Devon will also be affected by thick fog. "The heat rises and then it cools down and that is why you get fog forming".
Issued at - and valid from - 12:00pm today (Thursday, January 11), the weather warning will last until 2:00am tomorrow morning.
The warning covers Northern Ireland, Wales, north-west England, south-east England, West Midlands, Yorkshire and Humber and south-east England.
Forecaster Helen Roberts said: "Mists will quickly develop tonight turning readily into fog, mostly across western areas".
There are warnings that the "dense" conditions could cause travel disruption on roads with the possibility of some flights being cancelled or delayed.
He said: "Fog is expected to become increasingly widespread through Wednesday evening and overnight into Thursday". It is slowly lifting.
Met Eireann has this afternoon issued another Status Orange weather alert, warning that the fog may become more extensive and dense later this evening.
Still remaining rather cold with highs of 6C.
Britain is wrapping up for another chilly night with temperatures expected to drop to freezing widely with lows of -2C (28.4F) or -3C (26.6F) in rural regions.