CNA Explains: What is a heat dome? The weather pattern behind Europe's heatwave

World

Europe's current heatwave is fuelled by a weather pattern known as an Omega block, which creates a heat dome.

24 Jun 2026 07:22PM

(Updated: 24 Jun 2026 08:08PM)

SINGAPORE: Europe is experiencing a major heatwave, with high temperatures disrupting daily life across the continent.

In France, more than 90 per cent of the population is facing extreme heat. Temperatures are set to reach between 39°C to 41°C on Wednesday (Jun 24) from Brittany to Paris and across much of the southwest.

French authorities said on Tuesday that at least 40 people have died in incidents linked to the heatwave since the weekend. Many drowned while swimming in unsupervised areas.

In Italy, the health ministry on Wednesday declared a red heatwave alert for 16 cities, including Milan and Rome.

The hot weather is expected to extend into eastern Europe in the coming days.

The current heatwave is fuelled by a weather pattern known as an 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, according to meteorologists.

This creates a so-called heat dome - a high-pressure system that traps hot air over western and central Europe, causing temperatures to rise day after day.

But what exactly is a heat dome, and why does it cause temperatures to soar?

What is a heat dome?

A heat dome is an area of high-pressure air in the atmosphere that becomes stuck over a region because atmospheric dynamics around it block it from moving.

The high-pressure system would remain stationary for a few days, trapping dangerous heat and humidity underneath it, said Mireia Ginesta, a research associate at the Climate Litigation Lab at the Smith School of Enterprise and the Environment.

The high-pressure system traps hot air below it - which heats up and compresses to form a dome.

This increases the heat and prevents the formation of clouds, which enables more radiation from the sun to hit the ground.

A heat dome will result in clear, sunny days, and still conditions with little cooling wind

Such systems can last for days to weeks.

“High-pressure system means that the air is sinking, and as the air goes down to lower altitudes, it becomes compressed,” Ginesta said. “So the pressure increases and the temperature also increases.”

In short, this high-pressure system acts like a lid on a pot. Hot air near the ground becomes trapped, while sinking air gets compressed and warms further, creating a "dome".

A heat dome can also lead to storms and is part of this weather event's volatile pattern. Storms were expected over the Alps and Apennines, bringing heavy rain, gusty winds and hail.

What about heatwaves?

While a heat dome is a weather pattern in the atmosphere that traps heat, a heatwave is what people experience on the ground as a result.

A heatwave is defined as an extended period of hot weather where temperatures are above the historical average in an area for two or more days.

The World Meteorological Organisation (WMO) does not use a single global temperature value to define a heatwave.

Instead, it uses local thresholds, as what might be normal weather for one region may not be the same for another.

In short, it is dependent on local climate conditions, said WMO.

For example, temperatures above 30°C in parts of Norway, Sweden and Finland in 2025 were some of the worst heatwaves recorded for that part of the world, however, for tropical regions such as Southeast Asia, those numbers are common.

Does this phenomenon only occur in Europe?

No. This phenomenon is not unique to Europe and has been observed in America, Asia and Australia.

This phenomenon occurs in both hemispheres across the world's middle latitudes, said Samantha Burgess from the European Centre for Medium-Range Weather Forecasts.

In South Asia, parts of India and Pakistan were hit by intense heatwaves in May, with temperatures approaching or exceeding 45°C.

Australia also experienced this phenomenon in January, and temperature records were broken.

The US also faced something similar, with the National Oceanic and Atmospheric Administration in 2023 warning of high and dangerous heat across several states, with some temperature records broken in Texas.

At the time, the US National Weather Service's weather prediction centre said that the event might be more dangerous than others because of how long it lasted, with high temperatures persisting for days.

What do people experience during this weather event?

When extreme heat persists, it can have serious impacts on people's health and daily life.

Prolonged exposure to high temperatures can lead to heat-related illnesses ranging from heat cramps to fainting and heat stroke.

Extreme heat can also worsen some existing mental health conditions, while exposure to heat can affect sleep, concentration, reaction time and productivity, said WMO.

Beyond health impacts, the heat could also cause drought, wildfires and air pollution.

The current heatwave is already disrupting daily life and business activity across Europe.

In France, businesses have been implementing measures to protect their employees. Patrick Martin, the head of France's MEDEF employers group, said the country was operating at a slower pace as companies adjusted their operations.

Amid surging demand, some shops in Paris had reportedly also run out of electric fans.

The heat has also put pressure on infrastructure, with France suffering its first major power outage from the latest bout of extreme weather. The incident left 68,000 households in northwestern France without electricity.

Schools have been forced to close in parts of Europe, and transport services are also affected, with extreme temperatures putting additional strain on train systems.

In some cases, train systems will automatically shut the air-conditioning if they overheats, prompting operators to cancel services on the most exposed routes as a precaution.

Italy's health ministry has also placed 16 cities, including Milan and Rome, under its highest-level red heatwave alert. In the UK, the meteorological office has issued a rare red heat warning for parts of central and south England - only the second time such a warning has been issued.

Is a heat dome linked to climate change?

Scientists say the current heatwave is making extreme events more likely and severe.

A recent scientific study found that the current heatwave in Europe was "significantly exacerbated by human-induced climate change".

Without global warming, temperatures would have been 2°C to 4°C lower.

Research also found that climate change may make heat domes more frequent and intense. A 2022 study found that global warming made heat dome events up to 150 times more likely.

Scientists also confirmed that climate change is making heatwave events more intense, frequent and widespread.

A previous heat dome event in June 2025 in Europe could be linked to climate change and its effects on heatwaves, according to a Reuters report.

Climate change is not only increasing heat extremes but is also contributing to more intense storms and other weather events.

Europe is also warming at more than twice the global average, according to WMO, making such prolonged heat episodes increasingly likely.

Meteorological experts said the trend is likely to continue.

In a 2025 interview with Time magazine, Gordon McBean, professor emeritus at Western University, said that as the climate warms, the number and intensity of heat domes could increase, and the temperatures trapped beneath them could become even hotter.

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Source: Agencies/fh(rj)