Temperatures are forecast to plunge to freezing across North Wales later this week as colder weather spreads south.
The latest Met Office forecast shows temperatures falling to 0C in parts of North Wales on Thursday night.
The sharp drop comes as the Met Office says colder conditions will spread further south across the UK later this week, with frost becoming increasingly widespread.
Before then, the region faces another night of dense fog, with a yellow weather warning in force from 6pm on Monday until 10am on Tuesday.
Forecasters say fog will redevelop during Monday evening and become dense at times overnight, with visibility potentially falling below 100 metres in places.
The warning covers Wrexham, Flintshire, Conwy, Denbighshire and Powys.
Tuesday will bring a change in the weather, with cloud and outbreaks of rain spreading north across much of England and Wales.
The Met Office forecast for Wales says fog will gradually clear before rain spreads into southern parts during the morning and reaches most areas later in the day.
Temperatures across Wales are forecast to reach a maximum of around 10C.
Cloud and patchy rain are expected to continue on Wednesday, although conditions should become drier and brighter for many during the afternoon.
Colder air will then spread further south during Thursday and Friday, resulting in the drop towards freezing currently forecast for Wrexham and parts of Flintshire.
Jason Kelly, Met Office Chief Meteorologist, said: "Persistent high pressure has brought light winds and clear skies, allowing fog to form, while weak November sunshine has meant it is fairly slow to clear.
"We’re expecting one more night of dense fog, with a warning in place for some areas. Increasing cloud and wind should then limit further widespread fog from developing."
These colder conditions are expected to coincide with a return to more settled weather.
The Met Office's longer-range outlook says high pressure will initially dominate from Friday, bringing widely settled conditions and overnight frost.
The change may prove short-lived, however, with Atlantic weather systems expected to become increasingly influential later in the weekend, bringing a greater chance of wet and windy weather and temperatures moving back towards average.
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