What is a heat dome that has left Europeans sweltering in the heat?

England, France, Germany, Italy and large parts of Europe are all sweltering at once. With temperatures approaching 40 degrees Celsius, a severe heat wave swept across the region on Sunday (June 21), coinciding with the Northern Hemisphere's summer solstice.

Meteorologists say that this heat wave is caused by a mass of hot air moving north from the Sahara. This hot air is driven by a solid high-pressure system called the "African anticyclone."

The high-pressure system is creating a "heat dome", trapping hot air over Western and Central Europe, resulting in temperatures to climb every single day.

But what is a heat dome? And how is it bringing chaos in Europe?

We take a look.

What is a heat dome?

A heat dome forms when high pressure remains over the same area for several days or even weeks. It then traps warm air underneath it, just like a lid clamped on a simmering pot. As the hot air expands, it forms a "dome" that bulges outward.

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This phenomenon drives temperatures progressively higher during the day, often pushing them beyond seasonal averages since warm air becomes compressed over a smaller region.

According to the Royal Meteorological Society (RMS), warming ground and increased moisture evaporation create conditions that allow temperatures to keep rising.

The Met Office forecasts that these conditions will persist across large parts of central and northwestern Europe in the coming days, with temperatures expected to soar by up to 10°C above the seasonal average for mid-June, the Independent reported.

Spain, France and Italy may see temperatures rise into the high 30Cs, with some areas exceeding 40C.

The United Kingdom, on the other hand, could see a varied and complex pattern. This may happen when warm air from Europe moves northward and contrasts with low pressure in the northwest. Meaning, the northern and western parts of the UK are expected to experience spells of rain due to cooler weather, whereas southern and eastern areas will heat up as temperatures rise.

How is the heat causing chaos in Europe?

Authorities in Italy issued red alerts for eight cities, including Bologna, Florence, Milan and Turin, following days of temperatures above 35°C.

In Rome, pilgrims assembled in St Peter’s Square under umbrellas and parasols as Pope Leo XIV led the traditional Sunday prayer.

In France, the transportation network is disrupted by extreme heat. Officials in some 35 departments, roughly a third of the country, are on red alert.

While speaking at Paris’ Gare Montparnasse station, SNCF chief Jean Castex said the French rail network is "strongly impacted" by rising temperatures. According to Castex, it can destroy overhead power lines and expand railway tracks, the DW reported.

Authorities cancelled 71 intercity services on major routes until today (June 22), as thousands of rail workers were deployed to monitor tracks and carry out urgent repairs, Reuters reported.

Spain's weather agency, AEMET, issued red and orange alerts across several regions as temperatures are forecast to reach 39–40°C in large parts of the Iberian Peninsula and Mallorca.

The prolonged heat is exacerbating the wildfire. A rescue centre near the Belgian city of Namur reported taking in around 150 animals suffering from heat-related distress in recent days, with young birds among the hardest hit.

CREAVES founder Romain De Jaegere told Reuters, "Nestlings prefer to jump rather than let themselves die and literally cook in their nests."

In Germany, too, heat warnings remain in place as temperatures have climbed to 38°C. According to experts, such extreme heatwaves are becoming more frequent and intense because of climate change.

Over 200,000 people in Europe have died due to heat-related causes in the last four years, with a significant number of those fatalities considered preventable, Associated Press (AP) reported.

The World Health Organisation’s (WHO) Europe office has cautioned that above-average temperatures are expected again this summer, prompting emergency preparedness measures across Europe, Times of India (TOI) reported.

With inputs from agencies