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Spokane, Washington  Est. May 19, 1883
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Weathercatch: Take a look at the wave-like cloud so rare that it didn’t get named until five years ago

These rare asperitas clouds spotted over Pullman on the evening of May 26 resembled upside-down rippling ocean waves.  (Courtesy of Eric Loz)
These rare asperitas clouds spotted over Pullman on the evening of May 26 resembled upside-down rippling ocean waves. (Courtesy of Eric Loz)
By Nic Loyd and Linda Weiford For The Spokesman-Review

A formation of clouds that appeared above the Palouse on May 26 is so rare that it was only officially named five years ago.

Resembling dark, choppy ocean waves, asperitas, meaning “roughness” in Latin, roiled across the sky about 7:30 that Thursday evening. A number of onlookers captured the dramatic cloud display in photographs they shared on social media, including the one accompanying today’s column.

Asperitas is among the most recently recognized cloud types, so think of it as the new cloud in town.

The Cloud Appreciation Society petitioned to have it officially named in 2009. Eight years later, that’s what happened, when the Geneva-based World Meteorological Association added asperitas to the International Cloud Atlas in 2017. When published, it became the first new classification of a cloud in 54 years, according to cloud society founder Gavin Pretor-Pinney in his book “A Cloud a Day.”

The global cloud atlas describes asperitas’ appearance as “if viewing a roughened sea surface from below,” adding that its chaotic, wave-like configuration forms at the base of stratocumulus or altocumulus clouds.

It’s not as if asperitas formations suddenly started to appear in the new millennium. They’ve always been around. However, because they’re so rare, it took photographs shared on social media by citizen scientists and lobbying by the Cloud Appreciation Society to get the cloud type officially recognized.

Although asperitas clouds don’t produce rainfall, their presence often means a storm or weather front is nearby. Research suggests they are formed by complex and turbulent air currents at lower levels of the atmosphere, according to the journal Weather, published by Britain’s Royal Meteorology Society.

Sure enough, when they appeared overhead on May 26, a minor weather disturbance that had moved into the region interacted with low-level atmospheric instability. And yes, a brewing storm was nearby, but nothing like the system that drenched the Inland Northwest on Sunday and Monday of this week. That dramatic downpour was fueled by a strong atmospheric river, considered highly unusual for the month of June.

Conversely, the asperitas clouds on display three weeks before are highly unusual any time of year. If you’re lucky enough to spot these fleeting dark waves one day, snap some pictures before they churn from sight.

Nic Loyd is a meteorologist in Washington state. Linda Weiford is a writer in Moscow, Idaho, who’s also a weather geek. Contact:

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