At eleven in the morning, a British visitor was seen enjoying a Pina Colada. "It's really hot." In May of this year, he was walking around cities in Europe when he told France24, "It's absolutely boiling."
Severe heatwaves are plaguing Europe, including the UK. Europe is experiencing abnormally high temperatures because of the "heat dome," a pocket of warm air trapped under a high-pressure system.
Tuesday's extremely high temperatures exposed millions of people throughout Europe, and in the last week, 40 drowning deaths were reported in France as locals sought shelter from the intense heat.
With temperatures predicted to reach at least 39°C on Wednesday and Thursday—breaking June's all-time daily record temperature—the UK MET issued a "Red Extreme Heat Warning."Forecasters in France predicted that this week's temperatures in Paris could reach 40 degrees Celsius, a record for June. "Exceptionally high temperatures, both day and night," according to Mühlo-France, were anticipated.
In addition to warning of temperatures reaching 40 C (104 F) in the generally temperate Cantabria and the Basque Country areas along its northern Atlantic coast, Spain's national meteorological agency, Aemet, issued red alerts on Tuesday for temperatures of 44 C (111 F) in southern Andalusia.
The so-called "heat dome" is the cause of this unusually hot weather, according to a number of specialists and studies.
According to the New York Times, "heat domes occur all over the world, and the one over Europe this week is locking in days of near-record highs across Britain, Spain, and France."

A heat dome: what is it?
According to a UNDDR video, a heat dome is created when a large bubble of high-pressure air parks over an area.It reads, "It traps heat like a pot lid."
The agency claims that this occurs when the jet stream, a high river of air that typically propels weather systems forward, slows down or becomes stranded.
Extreme weather conditions like heat waves, heavy rains, or wildfires become stuck there for days or weeks.

The block of Omega
Heat domes and omega blocks are related but distinct. In short, the "heat dome" is the result of the Omega Block.
According to a meteorological analyst cited by Reuters, the severe, slow-moving European heatwave is being caused by a so-called "Omega block" weather pattern, which has prompted heat warnings to be issued by authorities around the continent.
According to the research, the pattern is referred to as a "Omega block," with colder air masses on either side and a dome of hot air trapped in the center.
The reason it's called Omega Block is that it resembles a Greek letter, with hot air bulging in the center and cooler air on either side, allowing temperatures to rise daily.

According to the Royal Meteorological Society (RMS), blocking conditions like an omega block—where high pressure finds up sandwiched between two low-pressure systems, generating a shape resembling the Greek letter Ω—can result from the position and strength of the jet stream.
Strong winds high above the Earth's surface are known as the jet stream, and they aid in the development and movement of low pressure zones. They frequently go from east to west, "but sometimes they can get blocked, often when the jet stream weakens and buckles."
Weather fronts can skirt around the high's boundaries or come to a complete stop as a result of the high pressure preventing them from passing through.The weather you experience will depend on where you are beneath the omega block.

"Below the dome"
The issue with a persistent area of high pressure, according to the Royal Meteorological Society (RMS), is that the already warm or hot air trapped beneath the high will get hotter and hotter, forming a heat dome.Hot air will rise into the atmosphere, but it will sink or subside due to high pressure acting as a lid. Heat increases as the air warms due to compression as it sinks. Additionally, the ground warms, releasing moisture and facilitating further heating.It continues, "The high will continue to intensify the hot conditions, bringing a risk of wildfires, drought, and heat-related health problems until the pressure pattern changes."According to experts, these patterns are becoming more often due to human-caused climate change.
Why is it getting so hot in Europe?
On June 17, the UK MET reported that a strong area of high pressure developing over continental Europe is driving the heatwave."The UK is caught between two air masses," it said. "This high pressure is encouraging widespread sinking air, which suppresses cloud formation, allows for prolonged sunshine, and leads to increasing temperatures through compressional heating."
The UK will see a more complicated and erratic pattern as Europe warms. According to the UK MET, low pressure to the northwest will continue to feed in regions with clouds, rain, and cleaner air.The growing plume of warmer air from the continent will try to travel north at the same time. With a so-called baroclinic zone—a barrier between warm and chilly air masses—positioned throughout or near the UK, this creates a stark contrast throughout the nation, it continued.
The effect? Weather fronts will form and move slowly along this boundary, bringing rain outbreaks, especially to the north and west.The UK MET also stated that this will cause a "waving" front, in which bands of rain alternate over comparable regions over a number of days.