Weathercatch: When a cloud mesmerized the Inland Northwest

On the morning of Feb. 18, 2015, a cluster of “punch hole clouds” wafted overhead. Scientifically known as cavum clouds, they are distinguished by giant circular or oblong holes that appear punched through a thin mid-level cloud layer.

What causes those openings? Primarily they’re left by aircraft passing through a wafer-thin layer of altocumulus clouds made of super-cooled water molecules. As the plane penetrates the cloud layer, the disturbance causes the water droplets to freeze into ice crystals that tumble downward like snow, leaving a hole in the cloud known as a dissipation trail. The opening can expand to a diameter of 10-30 miles over a period of several hours, according to Gavin Pretor-Pinney, founder of the Cloud Appreciation Society and author of several cloudspotting books.

When the cloud formation dazzled onlookers in our region that February morning in 2015, it didn’t even have a formal name yet. That came two years later when, in 2017, the cavum cloud was added to the International Cloud Atlas, the definitive reference book established by the International Cloud Atlas in 1896.

According to the National Weather Service Spokane, atmospheric conditions were ideal that morning after moisture that had drifted in from the west helped produce an expansive layer of altocumulus stratiformus. Then, each time a plane passed through, it punched a small hole that kept widening.

“We love clouds,” the Cloud Appreciation Society proclaims on its website. The cavum cloud is one big reason. By peering skyward every now and then, perhaps you’ll see clouds in a new light and come to love them as well.

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