The fog could be slow to clear and may linger into the afternoon on some roads.
Road users should be extra cautious as visibility could change without warning.
Drivers are advised to use dipped headlights or fog lights if visibility is seriously reduced (less than 100m/328ft).
Fog lights can dazzle other road users and obscure brake lights, so should be turned off immediately as visibility improves.
In patchy fog try not to speed up as visibility improves, as road users could suddenly find themselves back in thick fog further up the road.