Omega block is nature's secret weapon

The mechanism that brought floods to the Ile de France and a prolonged heatwave to the American Midwest is still not fully understood

An omega block might sound like a comic-book secret weapon, but it is a genuine meteorological effect, and was responsible for extensive flooding in Europe last month.

An omega block is an extreme version of a "blocking high", an area of high pressure which remains stationary for a prolonged period. It gets its name from the way that the jet stream bends around the high and the lows on either side of it, forming a shape resembling the Greek letter omega - I(C).