The weather system traps hot Saharan air beneath it like a lid on a pressure cooker. Directly underneath is France, where temperatures have reached 43C, prompting the country to shut schools, cancel trains and power down a nuclear reactor.

Europe is battling a deadly heatwave, with temperatures crossing 45°C and power systems under strain. Scientists say an Omega Block and climate change are driving the extreme heat.

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,

A blocking pattern will make for slow-moving weather. From a flood threat to upside down temperatures: here’s what we’re watching.

See more of our trusted coverage when you search. Prefer Newsweek on Google to see more of our trusted coverage when you search. A powerful atmospheric pattern known as an “omega block” is currently locking weather across the United States into place ...

The omega block is a weather term that describes the shape of the jet stream in the northern hemisphere: a curved upside-down "U" with two outward facing lines, which appears to resemble the 24th letter in the Greek alphabet, "Ω."