Parts of Europe are enduring a record-breaking early summer heatwave."France has just experienced its hottest night since measurements began in 1947," said Jason Nicholls, international meteorologist with Accuweather, speaking about the evening of June 23. "That follows the hottest afternoon ever recorded nationwide 37.8 °C (100°F)."The extreme heat has led people to seek relief in cooler waters. In France, 40 people have drowned in the past few days, the prime minister said on June 23.A powerful, high-pressure heat dome has spread across the continent, trapping a stagnant mass of superheated Saharan air. This unusually intense heatwave extends from the Iberian Peninsula to major Western European capitals. Several regions are expected to break their all-time heat records, which typically occur in July, according to Severe Weather Europe.Europe is warming at more than twice the global average, according to the World Meteorological Organization, making such prolonged heat episodes increasingly likely.Areas in Europe experiencing excessive heatUnable to view our graphics? Click here to see them.European heat waves can be especially dangerous because of relatively poor ability to mitigate the heat. Just about 20% of European households have air conditioning. By contrast, nearly 90% of American homes have some kind of AC. Reuters reported that in Paris, residents were facing sleepless nights in apartments ill-equipped for heat.What's causing Europe's heat wave?Jet streams naturally shift in broad loops known as Rossby waves. When these waves grow exceptionally large, they can stretch and constrict the flow, isolating a high-pressure zone between the northern and southern branches, according to the Weather.com."The heat is due to the upper low that developed over the Azores late last week," said Nicholls. The upper low has since moved closer to Spain and France. "The longevity is due to a blocking pattern over central Asia."Atmospheric blocks keep high-pressure systems stalled over an area for days or even weeks, leading to intense and prolonged periods of extreme heat, according to the Climate Adaption Center.Europe bakes under intense heatwaveResidents and tourists seek relief as extreme Europe heatwave pushes temperatures above 104 degrees amid widespread warnings.Impact of a heat dome in EuropeThe heatwave in Europe is coming from a heat dome, which is "an exceptionally hot air mass that develops when high pressure aloft prevents warm air below from rising, thus trapping the warm air as if it were in a dome," according to the National Integrated Heat Health Information System.When will Europe see relief from the heat?"The heat should ease from northwest to southeast across Europe starting this weekend," said Nicholls.According to Weather.com, London will endure intense heat through June 26, with conditions easing over the weekend. Paris, meanwhile, will remain in the grip of the heat through June 27, with thunderstorms on June 28 paving the way for cooler air to arrive by June 29.Across Germany, the heat wave will strengthen and persist through the weekend before moderating on June 29. In the broader Central European region, peak heat is expected from this weekend into June 29, followed by a gradual cooldown arriving between June 30 and July 1.CONTRIBUTING: Reuters, Julia Gomez and Jeanine Santucci/USA TODAY