Lenticular clouds, sometimes mistaken for UFOs, are in a league of their own

Lenticular Clouds Shrouding the Peaks of Mount McKinley (Getty Images/Ron Sanford)

On June 24, 1947, pilot Kenneth Arnold reported seeing multiple mysterious, gleaming circular objects along the crest of the Cascade Mountains in Washington. It was one of the most famous UFO sightings -- in fact, that was the exact moment the term "flying saucers" was coined.

An Air Force investigation later concluded that what Arnold really saw were disc-shaped wave clouds called lenticular clouds, which are not uncommon in the Cascades and on top of Mt. Rainier, the highest peak in the mountain range.

Lenticular clouds are different from other clouds because they don't form and move along but rather sit in one place, continually re-formed as air moves through them, causing them to morph slightly over time. They are the result of air rising to its condensation point over and downstream of an object, typically a mountain; however, they can also result from waves generated in the atmosphere itself.

A mysterious lenticular cloud forms over the Owens Valley,Eastern Sierra California. (Getty Images)

Mount Rainier is famous for its frequent lenticulars, as is Mount Fuji in Japan, and all tall mountains. When more than one lenticular layer appears on top of each other, they are referred to as "stacked lenticulars." But don't believe every photo you see on the Internet -- this photo of five layers over Mount Fuji is a hoax. This one is real:

Lenticular Clouds over New Zealand on August 29, 2020. (Geoffrey Beckett via Storyful)

Not surprisingly, the state of California has a lot of lenticular clouds due to its rapidly changing landscape from deep valleys to tall mountains. This classification of cloud has been featured many times in our "Weather Permitting" Photo Blog, including sightings of the formations during a wedding near Lake Tahoe in June 2023, during a brilliant sunset in the Sierra Nevada in May 2021, near Los Angeles in spring 2022 and at sunrise in Tehachapi, California, in January 2020.

Lenticular, or Sierra Wave Clouds, by Christopher Balladarez on May 25, 2021. (AccuWeather Photo Blog)

After Arnold's report, the UFO craze began to sweep the nation, sparking hundreds of copycat sightings. On July 8, 1947, as many as 30 residents of Montreal, Quebec, Canada, reported "a very large and dark object which consisted of two superposed discs which seemed to move close to each other if not to merge every few seconds."

Rénald Fortier from Ingenium, Canada's Museums of Science and Innovation suggests that the Montreal sighting might have been lenticular clouds as well. The description of superimposed large discs that merge certainly does sound like the wave clouds, perhaps a similar occurrence to lenticular clouds that recently scared residents over a South African town at night.

The cloud's form takes its name from the Latin word lenticularis, according to Merriam-Webster, meaning lentil-shaped. They are often saucer-shaped but can take many forms, including oblong and jellyfish-shaped.

From above on weather satellite images, they look like smooth blobs, as seen over Mount Etna below, or long smooth streaks.

A satellite image showing a lone lenticular cloud hovering above a snow-covered Mt. Etna in early December 2021 (AccuWeather Photo Blog)

Lenticular clouds don't necessarily portend any specific weather conditions. Although the clouds look like gentle giants, the wind is actually speeding quickly through them, rapidly moving up and down, and pilots may want to avoid the area around them because of turbulence.