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.
Prosecutors are considering whether to bring further criminal charges against Lucy Letby over the deaths of babies at two hospitals where she worked
The Crown Prosecution Service said it had received “a full file of evidence from Cheshire Constabulary asking us to consider further allegations in relation to deaths and non-fatal collapses of babies at the Countess of Chester Hospital and Liverpool Women’s Hospital”.
“We will now carefully consider the evidence to determine whether any further criminal charges should be brought,” it added.
“As always, we will make that decision independently, based on the evidence and in line with our legal test.”
Letby, 35, was found guilty of murdering seven children and attempting to murder seven more between June 2015 and June 2016 while working in the neonatal unit of the Countess of Chester Hospital and is currently serving 15 whole-life orders.
Letby worked at the Countess of Chester Hospital and Liverpool Women’s Hospital
She is understood to have carried out two work placements at Liverpool Women’s Hospital, where she trained as a student, between October and December 2012, and January and February 2015.
Police said in December that Letby was interviewed in prison as part of an investigation into more baby deaths and non-fatal collapses.
A Cheshire Constabulary spokesperson said: “We can confirm that Cheshire Constabulary has submitted a full file of evidence to the CPS for charging advice regarding the ongoing investigation into deaths and non-fatal collapses of babies at the neo-natal units of both the Countess of Chester Hospital and the Liverpool Women’s Hospital as part of Operation Hummingbird.”
Detectives previously said the investigation was looking into the full period of time that Letby worked as a nurse, covering the period from 2012 to 2016 and including a review of 4,000 admissions of babies.
Letby’s lawyer Mark McDonald said: “The evidence of the innocence of Lucy Letby is overwhelming,” adding: “We will cross every bridge when we get to it but if Lucy is charged I know we have a whole army of internationally renowned medical experts who will totally undermine the prosecution’s unfounded allegations.”
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Three managers at the hospital where Lucy Letby worked have been arrested on suspicion of gross negligence manslaughter.
On Tuesday, it was confirmed that three managers at the Countess of Chester hospital had been arrested on suspicion of gross negligence manslaughter in a separate investigation.
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Police said the suspects, who occupied senior positions at the hospital between 2015 and 2016, have all been bailed pending further inquiries.
There is also an investigation into corporate manslaughter at the hospital, which began in October 2023.
A public inquiry has also been examining the hospital’s response to concerns raised about Letby before her arrest.
In May, it was announced the inquiry’s final report into how the former nurse was able to commit her crimes will now be published early next year.
Earlier this year, Letby’s lawyers called for the suspension of the inquiry, claiming there was “overwhelming and compelling evidence” that her convictions were unsafe.
In February, an international panel of neonatologists and paediatric specialists told reporters that poor medical care and natural causes were the reasons for the collapses and deaths.
Their evidence has been passed to the Criminal Cases Review Commission (CCRC), which investigates potential miscarriages of justice, and Letby’s legal team hopes her case will be referred back to the Court of Appeal.
A power outage that shut Heathrow Airport earlier this year, causing travel chaos for more than 270,000 passengers, was caused by a “catastrophic failure” of equipment in a nearby substation, according to a new report.
Experts say the fire at the North Hyde Substation, which supplies electricity to Heathrow, started following the failure of a high-voltage electrical insulator known as a bushing, before spreading.
The failure was “most likely” caused by moisture entering the equipment, according to the report.
Two chances were also missed that could have prevented the failure, experts found, the first in 2018 when a higher-than-expected level of moisture was found in oil samples.
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Moment Heathrow substation ignites
Such a reading meant “an imminent fault and that the bushing should be replaced”, according to guidance by the National Grid Electricity Transmission.
However, the report by National Energy System Operator (NESO) said the appropriate responses to such a serious issue were “not actioned”, including in 2022 when basic maintenance was postponed.
“The issue therefore went unaddressed,” the report added.
The design and configuration of the airport’s internal power network meant the loss of just one of its three supply points would “result in the loss of power to operationally critical systems, leading to a suspension of operations for a significant period”, the report added.
Heathrow – which is Europe’s biggest airport – closed for around 16 hours on 21 March following the fire, before reopening at about 6pm.
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Heathrow bosses were ‘warned about substation’
Around 1,300 flights were cancelled and more than 270,000 air passenger journeys were disrupted.
Tens of millions of pounds were lost, thousands of passengers were stranded, and questions were raised about the resilience of the UK’s infrastructure.
More than 71,000 domestic and commercial customers lost power as a result of the fire and the resulting power outage, the report said.
NEOS chief executive, Fintan Slye, said there “wasn’t the control within their [National Grid’s] asset management systems that identified that this [elevated moisture levels] got missed.
“They identified a fault, [but] for some reason the transformer didn’t immediately get pulled out of service and get repaired.
“There was no control within the system that looked back and said ‘oh, hang on a second, you forgot to do this thing over here’.”
Sky’s science and technology editor, Tom Clarke, pointed to the age of the substation’s equipment, saying “some of these things are getting really very old now, coming to the end of their natural lives, and this is an illustration of what can happen if they are not really well maintained”.
The report also highlights a lack of joined-up thinking, he said, as “grid operators don’t know who’s critical national infrastructure on the network, and they don’t have priority”.
Responding to the report’s findings, a Heathrow spokesperson said: “A combination of outdated regulation, inadequate safety mechanisms, and National Grid’s failure to maintain its infrastructure led to this catastrophic power outage.
“We expect National Grid to be carefully considering what steps they can take to ensure this isn’t repeated.
“Our own Review, led by former Cabinet Minister Ruth Kelly, identified key areas for improvement and work is already underway to implement all 28 recommendations.”
In May, Ms Kelly’s investigation revealed that the airport’s chief executive couldn’t be contacted as the crisis unfolded because his phone was on silent.
Energy Secretary Ed Miliband, who commissioned the NESO report, called it “deeply concerning”, because “known risks were not addressed by the National Grid Electricity Transmission”.
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Mr Miliband said energy regulator Ofgem, which opened an investigation on Wednesday after the report was published, is investigating “possible licence breaches relating to the development and maintenance of its electricity system at North Hyde.
“There are wider lessons to be learned from this incident. My department, working across government, will urgently consider the findings and recommendations set out by NESO and publish a response to the report in due course.”
The Metropolitan Police previously confirmed on 25 March that officers had “found no evidence to suggest that the incident was suspicious in nature”.
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