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Driving on a lonely rural highway in Northwest Missouri in late winter 2017, my vehicle topped a hill and the sky was suddenly covered in clouds I’d never seen before – symmetrical waves dotted in charcoal, slate, and dove, like an impressionist’s representation of an angry ocean. I slowed to take it all in. A few weeks later I discovered why the clouds looked so strange. It’s a rare weather phenomenon that was only officially recognized by the World Meteorological Organization in March.

The asperitas cloud (Latin for “roughness”) was first brought to the attention of the UK’s Cloud Appreciation Society in 2006 when a cloud enthusiast forwarded the group a photograph taken over Cedar Rapids, Iowa. The photograph impressed the society enough it encouraged the World Meteorological Organization to include it in the International Cloud Atlas, the “the global reference for observing and identifying clouds.” In March 2017, the WMO updated the atlas for the first time since 1987.

“The International Cloud Atlas is the single most authoritative and comprehensive reference for identifying clouds. Its reputation is legendary among cloud enthusiasts and it serves as an essential training tool for professionals working in meteorological services, and in sectors such as aviation and shipping,” WMO Secretary-General Petteri Taalas said on World Meteorological Day.

The atlas describes the cloud formation as such: “Asperitas is characterized by localized waves in the cloud base, either smooth or dappled with smaller features, sometimes descending into sharp points, as if viewing a roughened sea surface from below.”

The description is certainly accurate.

A volutus cloud in Virginia. Photo by the National Weather Service Baltimore/Washington.

The society’s website boasts the new classification belongs to the public. “It is a classic example of citizen science, in which observations by the general public, enabled by the technology of smartphones and the Internet, have influenced the development this most official of classification systems.”

Asperitas was integral to the WMO updating its atlas, but it isn’t the only new cloud entered in the volume. New entries include volutus (roll cloud), murus (wall cloud) and cauda (tail cloud) which are both associated with thunderstorms, fluctus (clouds that resemble breaking waves), homogenitus (airplane contrails) and cavum (hole-punch cloud).

Although most of the additions are new names for known clouds, the cloud formation that is most interesting in regards to paranormal phenomenon is the cavum. On 7 November 2006, multiple witnesses, including numerous United Airlines employees, claimed to see a UFO over Chicago’s O’Hare International Airport. The round, grey vehicle shot straight into the sky leaving what resembled a hole punch in the clouds, per the Chicago Tribune.

A cavum cloud over Louisiana in December 2008 submitted to Weather.com by iWitness Weather contributor jamiecg.

Air traffic controllers didn’t witness a UFO, nor was there a blip on radar. Officials, such as O’Hare controller and union official Craig Burzych, had the expected response for the Tribune: “To fly 7 million light years to O’Hare and then have to turn around and go home because your gate was occupied is simply unacceptable.”

Airport officials blamed the strange hole in the clouds on a weather phenomenon, but what causes the hole-punch cloud formation like the one over O’Hare?

Per a 2013 article on weather.com, “these rare cloud formations, called ‘hole-punch clouds,’ develop in altocumulus cloud layers and are often the result of airplanes passing through the layer of clouds.”

So, the new classification, the cavum, gives a name for a cloud formation caused by an object flying through it because, per science, something certainly did.