Weather warnings have been issued across the UK over fears fog could disrupt the morning rush hour.
The Met Office says "slower journey times with delays to bus and train services" are possible in much of England, some areas of the Scottish borders and all parts of Northern Ireland on Tuesday.
Delays or cancellations to flights may also result from the reduced visibility, they added.
Major cities expected to be especially affected by the thick fog include Manchester, Birmingham, Nottingham and Sheffield.
Many other parts of the UK will also experience some fog, including some costal areas, though the warnings apply largely to places inland.
A yellow weather warning from the national forecaster said: "Areas of fog, dense in places, have developed and will be stubborn to clear through much of this morning.
"Whilst some fog is likely to persist all day, many places will see this lifting into low cloud or clear by this afternoon."
Their daily forecast meanwhile predicts that most parts of the country will stay dry, though persistent fog could see some chilly tempreatures.
Met Office advice for driving in thick fog includes "driving slowly with dipped headlights" and keeping an eye on speed, as fog can "give the illusion of moving in slow motion".
Some flood alerts are also in place today, including 35 given by the Environment Agency and one by Natural Resources Wales.
UK weather:
Areas of fog and low cloud slow to clear.
Today:
A few sunny spells but large areas of low cloud and fog will be slow to clear and may persist all day in places making it feel rather cold. Best of the sunshine expected across the far north and southwest.
Tonight:
Fog and low cloud developing more widely with any clear spells leading to an overnight frost, most likely in the north. A few spots of rain across Northern Ireland later.
Wednesday:
Many places cloudy with patchy fog, slowly lifting but persisting in a few places. Some sunny spells developing away from the northwest where some patchy rain will develop.
Outlook for Thursday to Saturday:
The north and northwest will see rain at times. Elsewhere, mostly dry with some fog and frost, but with scattered showers in the east and south. Feeling rather cold