From DW:
Europe was gripped by severe weather on Sunday as a prolonged heat wave set in across the region during the Northern Hemisphere’s summer solstice. Celebrated annually on June 21, the solstice also marks the start of Europe’s three hottest months.
According to meteorologists, the heat wave is being driven by a mass of hot air moving north from the Sahara, fueled by a strong high-pressure system known as the “African anticyclone.” The high-pressure system has created a so-called “heat dome,” which traps hot air over Western and Central Europe, allowing temperatures to climb day after day.