A yellow fog warning has been issued across Norfolk, with travel disruption expected.
The alert which covers the entire county and the surrounding areas, is in place until 11am on Monday, November 9.
Visibility could drop below 50 metres in some areas, raising concerns about delays on the roads and public transport.
People are being advised to allow extra time for journeys, check road conditions in advance, and ensure fog lights are working.
The Met Office alert said: "Fog will slowly lift and clear during Sunday morning; likely slowest across parts of the West Country and central southern England.
"Bus and train services, as well as flights and ferry travel, may also be affected; check for updates from your travel company and follow their advice."
The fog warning comes as forecasters warn of a polar vortex which is a ring of powerful winds that helps keep freezing air near the North Pole.
If it weakens, it could allow colder Arctic air to sweep south towards Britain, increasing the risk of wintry weather.
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