The Met Office has issued a yellow weather warning for fog across South Wales and South West England for this morning.
The warning has been issued from 5am to 11am for thick fog, mainly on hills and near the south coast. It covers large sections of the M5 and M4 and other major roads.
The latest weather and traffic news for Wales can be found here.
In an alert issued at 3.47am this morning, the Met Office said: "Very moist air, associated with a frontal system slowly moving northwards, is arriving into south-western parts of the UK.
"As cloud above it thins, and rain eases, this will allow a period of thick low cloud and fog to continue to develop, settle onto hills, and expand northwards with visibilities below 50 m in a few places.
"Fog should gradually lift into low cloud this morning, with visibility slowly improving."
The national weather forecaster said the conditions may make driving dangerous in some places and there is a chance of delays to flights.
The Met Office advises:
- Avoid travel if possible.
- Drive very slowly with dipped headlights, full-beam lights reflect off the fog causing a 'white wall' effect.
- Keep an eye on your speed, fog can give the illusion of moving in slow motion.
- Use fog lights, but remember to turn them off when the visibility improves.
- Don't hang on the tail lights of the car in front, rear lights can give a false sense of security.
- Watch out for freezing fog which is made of water droplets that freeze on contact with objects such as the pavement, road, car, etc. It can quickly form a layer of ice.
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