UK weather: What is a ‘heat dome’ – and how long will Britain’s hot spell last?
The UK is having a late summer burst of hot weather – while parts of the Mediterranean have been experiencing a phenomenon known as a “heat dome”, forecasters say.
Temperatures in Britain could soar as high as 32C (90F) this week, as much as 4C (39F) higher than Ibiza.
Here, Sky News looks at what is causing the unusually warm conditions in the UK and elsewhere in Europe – and whether we are set for an official heatwave.
People enjoy the hot weather in London’s St James’s Park
What is a heat dome?
A heat dome is loosely defined as an area of high pressure that stays over the same area for days, or even weeks.
Hot air is trapped underneath like a lid on a saucepan, pushing temperatures above what’s normal for the time of year.
The heated air expands upwards into the atmosphere, then high pressure from above acts as a lid, meaning it can’t escape and causes the air to subside or sink – creating a dome effect, the Royal Meteorological Society said.
As the warm air sinks, it compresses and heats up, which then traps more heat underneath and clouds are pushed around it, keeping the heat in even more.
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The Met Office says heat domes encourage temperatures “to keep building day on day”.
However, Sky weather meteorologist Dr Chris England said the phenomenon “doesn’t really apply to the current heat of the UK”.
He said that while a heat dome “has been relevant to some of the Mediterranean heat”, the high pressure affecting the UK “is well to the east”.
“Instead, the flow around the high pressure is generally from the south over the UK, bringing heat up from the Mediterranean and north Africa,” Dr England added.
The Met Office says tropical storms in the far western Atlantic, and deep areas of low pressure, have helped to amplify the jet stream over the Atlantic Ocean and has led to high pressure “dominating over the UK”.
Is the UK set for an official heatwave?
The word “heatwave“ is often used to describe any period of sunny weather, but the Met Office defines it as “an extended period of hot weather relative to the expected conditions of the area at that time of year”.
It says the UK experiences a heatwave when it has at least three consecutive days with daily maximum temperatures meeting or exceeding the heatwave temperature threshold – and this threshold varies by UK county.
Sky weather forecaster Kirsty McCabe said official heatwave conditions “will be met this week as temperatures soar over the next few days with a late blast of summer heat, especially for southern parts of the UK.”
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The peak is likely to occur on Wednesday and Thursday with 31C (88F) or even 32C (90F) possible.
The threshold temperature ranges from 25C (77F) in Scotland and Northern Ireland, to 28C (82F) in London and the Home Counties.
But Ms McCabe said “it’s not just hot weather heading our way, a Saharan dust plume will cross the UK, bringing some spectacular sunrises and sunsets”.
Hitting 30C in September “used to happen around once every seven years or less, but has occurred more frequently in the last decade,” she said.
Could we have the hottest day of the year this week?
This year’s highest temperature is 32.2C (90F) at Chertsey on 10 June and Coningsby on 25 June.
Ms McCabe said: “There is a chance we could exceed that this week [Wednesday or Thursday].”
The highest September temperature ever recorded in the UK was 35.6C (96F) in South Yorkshire in 1906.
Is this an Indian summer?
According to the Met Office Meteorological Glossary, an Indian summer is a warm, calm spell of weather that occurs in autumn, “especially in October and November.”
There is, the Met Office says, no statistical evidence to suggest that such warm spells recur at any particular time each year – warm spells during the autumn months are not uncommon.
How long will the UK’s hot weather last?
An amber alert is in place for the whole of England except the North East, where a yellow alert is in place.
The alert, issued by the UK Health Security Agency and the Met Office, is in place until 9pm on 10 September.
Temperatures reached 30C on Monday in southern England and the southeast of Wales, according to the Met Office – and the hot weather will continue through Tuesday, with highs of 31C (88F) expected.
Met Office spokesperson Oli Claydon said: “We will see good sunny conditions through the week with cloudless skies, and some high temperatures by the time we get to Wednesday and Thursday, where we could see 31 maybe 32 degrees.”
The Met Office said temperatures could also hit 31C (88F) on Friday, although there could be more cloudy weather and chances of rain in the far northwest of Scotland.
But the weather conditions could change over the weekend and Mr Claydon said there is “no indication at the moment of another strong heatwave after this”.
He added: “Through the weekend, we start to see some heavy, potentially thundery, showers developing but (they are) only isolated. There is a little bit of uncertainty as we start to get that far ahead.”
Average temperatures are expected to return by the middle of next week.
UK
Details of King Charles’s Christmas message revealed – as he chooses to deliver it away from palace
A photograph has been released by Buckingham Palace showing the King delivering his Christmas message again outside of traditional palace walls.
This year the annual address was filmed in the Lady Chapel inside Westminster Abbey, the second time the monarch has recorded it away from a royal residence.
The palace has revealed the abbey was chosen for the setting this year to reflect a major theme of the message, pilgrimage.
The Lady Chapel in Westminster Abbey, central London. Pic: PA
The full details of what he says are always kept secret until it is broadcast at 3pm on Christmas Day. The message is always seen as a deeply personal one from the monarch, as a rare speech delivered by the King without advice from, or consultation with, the government.
Westminster Abbey was seen as a perfect location to reflect the theme of pilgrimage with pilgrims visiting every year to remember the legacy of Edward the Confessor, whose shrine lies at the heart of the abbey. Around the walls of the Lady Chapel are 95 statues of saints dating from the building of the chapel in the 16th century.
Pic: PA
The abbey, as the site of the King’s own coronation and that of every monarch since 1066, also has royal significance. The Henry VII Lady Chapel is the burial place of 15 Kings and Queens including Elizabeth I, Mary I and Mary Queen of Scots. Below the central aisle is the Hanoverian vault where George II and members of his family are buried. The Stuart vault is in the south aisle where Charles II, William III and Mary II, and Queen Anne lie buried.
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It is understood the King takes a particular interest in where the message is filmed each year, favouring different locations outside of royal palaces over the past two years.
In the photograph, taken during filming, you can also see brightly lit Christmas trees used for another royal event in December. They were still inside the abbey following the filming of the Princess of Wales’s Together at Christmas carol service, which will be broadcast on Christmas Eve.
The prime minister has acknowledged Britons’ cost-of-living struggles in his Christmas message – and vowed that helping with the issue is his “priority”.
Sir Keir Starmer also urged members of the public to “each do our bit” and “reach out” to friends, relatives and neighbours during the festive period.
His message comes at the end of a difficult year for his government, with economic growth stuttering and Chancellor Rachel Reeves facing criticism over tax rises in the budget.
In a message recorded inside 10 Downing Street, Sir Keir said: “I know many across Britain are still struggling with the cost of living. Helping with that is my priority.
“But at this time of the year, which celebrates love and abundance, loss or hardship can feel even more acute.
“So call around to a neighbour. Check in on a friend or a relative who you haven’t heard from for a while. Reach out. It can make a huge difference.
“That is what Christmas is about.”
Sir Keir Starmer delivers his Christmas message from inside Downing Street. Pic: Downing Street
The prime minister thanked NHS workers along with members of the military and the emergency services who will be on duty on Christmas Day.
“Just as so many put their feet up, some truly special people will be pulling on their uniforms and heading out to work,” he said.
“Our NHS staff emergency services and the brave men and women of our armed forces, all playing their part, doing their bit to care for the nation and to keep us safe.
“Many volunteers will be out there as well. Serving food. Reaching out to help those lonely or in need.
“So on behalf of the whole country, I want to say a big thank you.
“As a nation, we should raise a glass to you this Christmas. But more than that, we should each do our bit as well.”
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Conservative leader Kemi Badenoch used her Christmas message to talk about “Christian values” and thanked “everyone who has supported me during my first year as leader of the opposition”.
“It’s been the biggest challenge of my life,” she said. “But it’s also been a wonderful year. I can’t wait to get back to work next year to create a better United Kingdom.”
Liberal Democrat leader Sir Ed Davey spoke about the Christmas tree in London’s Trafalgar Square – an annual gift from Norway to thank the UK for its support during the Second World War – in his message.
While saying the tree may “look a little underwhelming” on first glance, the Liberal Democrat leader said it was a reminder of “friendship and loyalty”.
He added: “It makes me think about people standing together in tough times – whether against the Nazis in the 1940s, or right now in Ukraine.
“And yeah, it might not be perfect, but this tree in Trafalgar Square makes me think about families and friends looking out for one another right here at home.
“I can’t think of a better symbol of the Christmas spirit of generosity, love and hope. Of light in the darkness.”
Many in the UK will wake up to a frosty morning on Christmas Day – but don’t hold out hope for snow, forecasters have said.
The Met Office says the 24 and 25 December will be dry and sunny for most, but a brisk wind picking up from Christmas Eve will make this year slightly below-average temperature wise.
It adds that for most of the country, it will feel close to freezing, with temperatures peaking at 4-5C across the festive period.
In Scotland, temperatures are forecast to plummet below freezing across much of the country, with the north of the country potentially reaching -5C.
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Keen swimmers looking for a bracing dip in the sea on Christmas Day and Boxing Day may potentially face big waves, due to easterly winds.
Despite the chillier temperatures, a white Christmas is not looking likely, with only a small chance of snowfall in Dartmoor and a 10% chance of “winter flurries” on the south coast of England.
Pic: iStock
“All we need, of course, is for a flake of snow to fall anywhere across the UK for it to technically be termed a ‘white Christmas’, so something to keep an eye on across the far south of England,” Met Office meteorologist Marco Petagna previously said.
Last year, not one snowflake was recorded anywhere in the UK on Christmas Day. In fact, temperatures were above zero everywhere.
The last time all four UK nations had a white Christmas was back in 2010, the year snow lay most widely across the UK since 1959.
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On Boxing Day, some southern counties could see more cloud, but elsewhere is expected to remain largely dry with sunny spells.
Similar weather is expected right up until New Year’s Eve, Met Office meteorologist Becky Mitchell said.
“It’s a bit colder than average, not unusual for the time of year, but in terms of averages it would be a bit below,” she added.
“The weather’s all very similar really, out towards New Year’s Eve. The Christmas period is quite a nice forecast.”
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