Europe heatwave: Sipping Pina Coladas at 11 am? Understanding why UK, France, Spain are getting so hot

A British tourist was spotted sipping Pina Colada at 11 am. “It's so hot. It's absolutely boiling,” he told France24 as he strolled through the streets somewhere in Europe in May this year.

Europe, including the UK, is reeling under brutal heatwaves. Thanks to the 'heat dome', a pocket of warm air trapped under a high-pressure system, which is driving unusually high temperatures across Europe.

Millions of people across Europe were exposed to extreme and exceptional high temperatures on Tuesday, with 40 fatalities from drowning recorded in France in the past week as residents seek relief from the searing heat.

The UK MET issued a 'Red Extreme Heat Warning' for Wednesday and Thursday, with temperatures expected to climb to at least 39°C -- breaking June’s all-time daily record temperature. "There remains a chance of this being exceeded in places, the MET office says in its forecast.

In France, forecasters said temperatures in Paris could hit 40 degrees Celsius this week, which would be unprecedented for June. Météo-France said “exceptionally high temperatures, both day and night,” were expected.

Spain’s national weather service, Aemet, also issued red alerts Tuesday for temperatures of 44 C (111 F) in southern Andalusia as well as warnings of thermometers hitting 40 C (104 F) in the normally temperate Cantabria and the Basque Country regions along its northern Atlantic coast.

According to several experts and reports, this unseasonably hot weather is being driven by a so-called "heat dome".

“Heat domes happen all over the world, and the one over Europe this week is locking in days of near-record highs across Britain, Spain and France,” the New York Times reported.

What is a heat dome?

A heat dome forms when a massive bubble of high-pressure air parks over a region, the UNDDR explained in a video.

"It traps heat like a lid on a pot," it says.

According to the agency, this happens when the jet stream — a high river of air that usually moves weather systems along — slows down or gets stuck.

When that happens, extreme events like heatwaves, torrential rain or wildfires get trapped in place for days or weeks.

The Omega block

Omega Block and heat dome are related to each other but not the same. Simply put, the Omega Block is the cause, and the 'heat dome' is the consequence.

Reuters quoted a weather analyst as saying that a so-called “Omega block” weather pattern is driving the intense, slow-moving European heatwave, prompting authorities across the continent to issue heat warnings.

The pattern is known as an “Omega block,” with a dome of hot air trapped in the centre and cooler air masses on either side, the report added.

It's called Omega Block because it takes the shape of the Greek letter, with a bulge of hot air in the middle and cooler air on either side, allowing temperatures to build day after day.

The Royal Meteorological Society (RMS) explains that the position and strength of the jet stream can lead to blocking situations, such as an omega block, where high pressure ends up sandwiched between two low-pressure systems, forming a shape like the Greek letter Ω.

The jet stream is strong winds high above the Earth’s surface that help to develop and steer areas of low pressure around. They often move east to west, "but sometimes they can get blocked, often when the jet stream weakens and buckles."

The high pressure stops weather fronts moving through, so they either skirt around the edges of the high or grind to a halt.

"Your position under the omega block will determine the weather you get. Under the high, the weather is usually dry and settled, whereas low pressure brings wet and windy conditions. Weather blocks can persist for days, weeks or even months, like in the summer of 1976," the Royal Meteorological Society (RMS) says.

‘Under the dome’

The Royal Meteorological Society (RMS) says that problem with a stubborn area of high pressure is that already warm or hot air trapped under the high will become hotter and hotter, creating a heat dome.

"Hot air will rise into the atmosphere, but high pressure acts as a lid and causes the air to subside or sink. As the air sinks, it warms by compression, and the heat builds. The ground also warms, losing moisture and making it easier to heat even more," it explains.

"Until the pressure pattern changes, the high will continue to exacerbate the hot conditions, bringing a risk of wildfires, drought and heat-health issues," it adds.

Experts say that human-driven climate change is increasing the likelihood of these patterns.

Why Europe is turning so hot

The UK MET said on June 17 that the developing heatwave is being driven by a strong area of high pressure building over continental Europe.

"his high pressure is promoting widespread sinking air, which suppresses cloud formation, allows for prolonged sunshine and leads to increasing temperatures through compressional heating," it explained.

'The UK is caught between two air masses'

While Europe heats up, the UK will experience a more complex and variable pattern. Low pressure to the northwest will continue to feed in areas of cloud, rain and fresher air, the UK MET said.

"At the same time, the expanding plume of warmer air from the continent will attempt to move northwards. This sets up a sharp contrast across the UK, with a so-called baroclinic zone – a boundary between warm and cool air masses – positioned across or close to the country," it added.

The impact? Along this boundary, weather fronts will develop and move slowly, bringing outbreaks of rain, particularly to northern and western areas.

"This will result in a “waving” front, where bands of rain ebb and flow over similar areas over several days," the UK MET added.