Each day, members of the Cloud Appreciation Society post photographs of intriguing clouds seen throughout the world. One day last month, the skies of southeastern Idaho were featured for an elegant cloud display resembling a spray of long eyelashes.
Meet cirrus fibratus, a cloud species you probably didn’t learn about in grade school when big puffy cumulus clouds got all the attention. Long, thin filaments arranged in rows, cirrus fibratus cloud formations are more ethereal than boisterous.
Even so, they’re a favorite among cloudspotters. On the early evening of Oct. 20, they attracted plenty of gawkers about 25 miles northeast of Idaho Falls near the town of Rexburg. Judging from comments posted on Facebook and Instagram, many people had no idea what the silky strands of clouds were called.
“Eyelash clouds,” one observer wrote. It didn’t take long for a global village of seasoned cloud watchers to solve the riddle: Cirrus fibratus, a species of the cirrus cloud elongated by the wind into a unique pattern.
Characterized by slender white parallel lines that fan out on the horizon, they’re composed of ice crystals that form above 20,000 feet, which translates to almost 4 miles away. At that altitude, temperatures run below minus-30 degrees and winds travel at very fast speeds.
It’s those strong, continuous winds that form the distinctive, orderly pattern of cloud filaments that resemble “hair run through a comb,” according to the Cloud Appreciation Society on its website. The strands align with the direction of the wind, the organization added.
Even though the fibratus species is common among cirrus cloud types, it’s not commonly seen. Why is that? For one thing, they don’t take up a lot of sky, so we’re less likely to look up and see them. Also, depending on the time of year, they may not be visible from the ground. Due to their high altitude, lower-level clouds can easily obscure them, especially during winter when we have more cloud cover.
Luckily for us, autumn is a good time to see cirrus fibratus – including here in the Inland Northwest. Compared to wintertime, there are fewer low clouds this time of year and also more daylight. That little-noticed backdrop overhead? Every now and then, look up. What you see may surprise you. Cirrusly.
Nic Loyd is a meteorologist in Washington state. Linda Weiford is a writer in Moscow, Idaho, who’s also a weather geek.