Wales could see the mildest New Year's Eve on record, with temperatures in the double figures during the day and night.
The Met Office forecast for today and New Year's Day is for "unseasonably warm" temperatures with highs of 14°C, and it could still be around 12°C at midnight as 2022 is welcomed in. But there is a change on the way with colder temperatures by next Wednesday.
Temperatures are expected to plummet to 6-9°C in southern parts of Britain and 5-6°C in northern areas from Bank Holiday Monday on January 3.
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Met Office meteorologist Rachel Ayers said there was a "good chance" of New Year's Eve being the mildest ever.
She said: "In the south of the UK the weather should be dry for New Year's Eve so people should be able to enjoy dry weather with some bright spells around. For New Year's Day, another band of rain is pushing in from the west so the further east you are the drier your day will be with some bright spells."
Check the weather for your area:
The forecast for Wales on Friday says: "New Year's Eve will start rather dull and grey, however skies should break readily during the morning with some decent sunny spells developing. Feeling very mild with winds easing. Maximum temperature 14°C.
"Variable amounts of cloud with clear spells here and there particularly across eastern areas, remaining cloudier in the west. Outbreaks of rain around midnight, though these quickly clearing. Staying mild. Minimum temperature 9°C.
"On Saturday, a band of cloud and rain quickly arrives pushing eastwards during the day, sunny spells following. Rather windy and mild. Maximum temperature 13°C."
The outlook shows a band of rain edging south on Tuesday that will introduce "colder conditions" later in the day.
Recent very mild temperatures on New Year's Eve include in 2018 when Dunrobin Castle Gardens, Sutherland, reached 14.5°C and 2011 when Colwyn Bay reached 14.8°C.
The Colwyn Bay maximum is the highest in the Met Office's digitised database which contains stats going back to the 1850s.
The December record in Wales is 18°C at Abergwyngregyn, Gwynedd, in 1972.
The UK has seen less than 27 hours of sunshine across the past 30 days - 38% less than the national average for this time of year, according to the Met Office.
The figure places this month in the running to become one of the top 10 dreariest Decembers on record, Met Office forecaster Craig Snell said on Thursday.
Britain's dullest December ever was in 1956 when 19.5 hours of sunlight was the national average, while the sunniest was in 2001, with 64 hours recorded on average across the UK.
The cause of this "exceptionally" mild and dim December was Atlantic winds, the Met Office said.
Ms Ayers said: "It has been quite mild and cloudy through December and a reason for this is we have been drawing south-westerly winds from the Atlantic bringing with it a lot of moisture which produces a lot of cloud, hence the duller and milder weather."
Met Office forecaster Aidan McGivern said that "interesting things" happen towards the end of the weekend as a "dip in the jet stream" approaches the UK.
He added: "The dip will push the jet stream to the south of the UK, which will eventually bring colder weather to our shores for the start of next week.
"It is going to change through Monday and Tuesday eventually. The first signs of change will come as we end Sunday and go into Monday as colder, northerly winds arrive into Scotland. It is going to feel colder everywhere, and Tuesday is likely to turn colder again. More like the average for the time of year.
"It looks like any colder spell next week will only last 24 to 48 hours, and we are not overly concerned about any wintry hazards."
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