The Met Office is warning of fog or freezing fog patches becoming widespread today.
The warning which is in place across the North West is from 3pm on Monday, December 24 to 11am Tuesday, December 25, 2018.
While it remains unclear where will be affected by the conditions, visibility could fall to below 50 metres where fog does form and will be slow to clear on Christmas Day.
A Met Office spokesman said: "It could be quite dense from this evening and through the night tonight."
"It will be a grey start for most. In the east it will be mostly dry, an odd spot of drizzle is possible in the west."
Temperatures are expected to be average for the time of year, with 5-9C (41-48F) predicted in the east and 11-12C (51-53F) in the west.
Later in the week there will be a mixture of misty conditions and sunny spells, with the potential for overnight frost if skies are clear.
What to expect
Slower journey times with delays to bus and train services possible
There is a chance of delays or cancellations to flights