Britain is enduring a record-breaking heatwave, with temperatures surpassing June highs for three consecutive days.
A rare red warning for extreme heat remains in place until 9pm for London, the South East, and the East of England.
The Met Office states the heat will bring "high humidity, exacerbating the potential for discomfort and health impacts."
This unseasonably hot weather is driven by a ‘heat dome’ – a significant area of trapped high pressure – building across Europe, triggering scorching temperatures continent-wide.
Here we explore what causes a heat dome and how a heatwave is defined.
What is a heat dome?
A heat dome is created when a high pressure area stays over the same area for days or potentially weeks, trapping very warm air underneath it, like a lid on a saucepan. Because hot air expands, it creates a ‘dome’ that bulges out.
This weather phenomenon causes temperatures to become hotter and hotter, building through the day and rise above what is considered normal, since warm air becomes compressed over a smaller region.
The ground warms as well and moisture evaporates, the RMS says, making it easier for temperatures to continue to rise.
These weather systems and their prolonged heat also increase the risk of wildfire and heat-related health problems, the Royal Meteorological Society (RMS) said.
Often these pressure systems move east to west, the RMS explains. Sometimes they can be blocked when the jet stream of strong winds high in the atmosphere weakens.
Large parts of central and northwestern Europe have been covered by these conditions over the past week, with temperatures expected to reach 10C above mid-June averages, according to the Met Office.
Spain, France and Italy saw temperatures rise high into the 30Cs and early 40Cs.
Meanwhile, the UK has seen a more varied and complex pattern, as the warm air moving northwards from Europe met with low pressure in the northwest. This means northern and western parts of the UK saw repeated spells of rain due to the cooler weather front, while southern and eastern areas experienced sweltering temperatures.
What is the definition of a heatwave?
A heatwave is simply a prolonged period of abnormally high temperatures. What is considered an abnormally high temperature varies from place to place.
Paris has imposed a ban on public alcohol consumption from Friday afternoon as it battles a relentless heatwave. The extreme weather has been linked to hundreds of deaths, widespread forest fires, and numerous event cancellations across the continent.
The restrictions in the French capital began at midday, with temperatures hitting 36C, and will continue all weekend in a desperate bid to curb excess deaths. Paris recorded a June high of 40.9C on Wednesday. Authorities also report at least 55 people, many young, have drowned across France since 18 June seeking relief from the heat.
Two elderly people died of heatstroke in Spain, which has experienced extreme temperatures since the weekend exceeding 40 C.
Temperatures there were starting to slightly ease on Wednesday into the 30s, before returning to more bearable conditions by the weekend.
But the weather will take another turn towards the end of the weekend and into next week, with temperatures returning to the low 40s in the southwest and in parts of southern Portugal.
A long-range forecast by Ventusky shows that some areas of southern Spain, near Sevilla, could hit as high as 45C on 4 July.
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