Air normally moves significantly more horizontally than vertically. When moist air is forced upwards over a high geographic feature like a mountain or volcano, lenticular clouds can form as the air cools and water moisture condenses.
Visual characteristics of lenticular clouds
A type of wave cloud, the word lenticular originates from the Latin word Lenticularis which means lentil-shaped. Because they appear to cap or hang over mountain tops, these clouds are also often referred to as “cap clouds” or “UFO clouds” (after the cloud’s flying saucer-like shape).
How Lenticular clouds form
As fast moving horizontal air meets a topographic barrier like a mountain, the air is forced up and over the mountain, creating atmospheric waves. The rising air cools at the top of the mountain and condenses water vapor in the air, forming the curved and layer shapes typical of a lenticular cloud.
What sets lenticular clouds apart from other cloud types is their relative immobility. While most clouds are carried along by winds, lenticular clouds tend to remain in place. Lenticular clouds seem to remain stationary, even for extended periods, despite being subjected to strong horizontal winds. However, this appearance is somewhat deceptive. In actuality, these clouds are in a constant state of formation and dissipation. They form around the peak of an air wave and then disintegrate shortly after passing that point.
Where are lenticular clouds found in the United States?
Lenticular clouds are common in the mountainous regions in North America like the Rocky Mountains, extending from Canada through the United States to New Mexico, due to the region’s particular topographical and atmospheric conditions. The mountainous terrain creates the necessary conditions for air to be lifted and cooled, leading to the formation of these distinctive clouds. The Rocky Mountains act as a barrier that disrupts the horizontal flow of air masses.
In western part of the United States, lenticular clouds tend to form when the atmosphere above the mountain is stable, typically around 10,000 feet. For example, The Sierra Nevada mountain range in California and Nevada also provides ideal conditions for lenticular clouds. The high peaks and the surrounding landscape cause air to rise and cool, contributing to the development of these clouds.
New Zealand’s named lenticular cloud: Taieri Pet
The skies over Middlemarch, Otago on South Island in New Zealand are home to a unique lenticular cloud that has its own name: Taieri Pet. Taieri Pet typically occurs when northwestern winds move over and down the cliffs of the Rock and Pillar Range. The lenticular cloud forms at the peak of those descending winds, where the air is coldest, leading to condensation.
The resulting lenticular cloud is long and elongated, a result of the prevailing northwestern winds flowing perpendicular to the Rock and Pillar Range. This Landsat 8 satellite image shows the formation of New Zealand’s most famous lenticular cloud on September 7, 2024.
Using lenticular clouds to study gravity waves
As air rushes over mountains, gravity waves can form under the right conditions. Lenticular clouds can form at the crest of the gravity waves if the conditions of cold air and water vapor are present.
Jim Peaco, NPS, November 2014, public domain.
Satellite imagery captured this lenticular cloud forming over the top of Mount Michael, an active stratovolcano in the South Sandwich Islands.
References
Hansen, K. (2021, January 19). Curious clouds in the Transantarctic mountains. NASA Earth Observatory. https://earthobservatory.nasa.gov/images/147772/curious-clouds-in-the-transantarctic-mountains
LeFevre, K. (2020, December 28). The case of the missing waves. Earthdata. https://earthdata.nasa.gov/learn/sensing-our-planet/the-case-of-the-missing-waves
Millar, C., & Oakley, N. (2013). Lenticular Clouds Revisited. Mountain Views Newsletter, 47.
Worthington, R. M. (2002). Lenticular wave cloud above the convective boundary layer of the Rocky Mountains. Weather, 57(3), 87-90. https://doi.org/10.1002/wea.6080570303
This article was originally written on December 6, 2021 and has since been updated.
