In March, the World Meteorological Organization added some new cloud-types to its International Cloud Atlas for the first time since 1951.
One such was Asperitas, describing “well-defined wave-like structures in the underside of the cloud; more chaotic and with less horizontal organisation than the variety Undulatus”.
Hobbyists and cloud enthusiasts have been agitating for the new type to be recognised for several years, under the name undulatus asperatus. The video above shows one formation looming hypnotically over Nebraska, USA, in 2014. The cloud base swells and melts, pinched into wavy peaks like an inverted imitation of a stormy seas.
The formations are particularly common over the southern plains of the US, often during the day, following a thunderstorm. They don’t necessary herald more bad weather, despite their thrillingly apocalyptic appearance.