FOG warnings are in force for much of Britain this morning.
Visibility will be severely reduced across England, Scotland and Northern Ireland sparking fears of widespread travel chaos.
Forecasters have urged motorists to take care on the roads or to avoid driving where possible.
And bus and train services could be delayed, with a chance of flight cancellations over safety fears.
Planes are already been diverted from Leeds Bradford Airport because of the dangerous conditions.
The Met Office's yellow fog warning stretches from Portsmouth to Middlesbrough and Carlisle in England, and Dumfries and Galloway in Scotland.
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It also covers most of Northern Ireland and is in place until 11am.
The "dense" and "stubborn" fog will likely persist all day.
Temperatures will hover in low single figures before lunchtime, rising to highs of just 11C by this afternoon.
But it will remain mostly dry, with just a smattering of light showers.
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The best of the sunshine is expected in the far north and southwest.
Patchy fog will continue into tomorrow before clearing by the end of the working week.
The weekend is looking mostly dry with some frost and will feel "rather cold".
Met Office meteorologist Clare Nasir said: "Pressure is building across the UK which means it's turning drier and colder with an increasing chance of frost and fog.
"If you're stepping outside this morning, wrap up warm and be aware that fog could be dense so some tricky driving conditions and poor visibility.
"Through the morning, this stubborn fog will linger with a real mix into the afternoon.
"Temperatures will really struggle; it's going to be a dull day and a cold one with temperatures below average for this time of year.
"Further into the week, cold dense air will migrate from the North Sea with tumbling temperatures.
"Wherever you are, there will be dry weather but cold with a risk of fog, frost and some chilly old days."