What Are Lenticular Clouds?

How Lenticular Clouds Form

• Lenticular clouds are formed by stable, warm, moist air that rapidly flows over mountainous terrain. As the airstream passes over and around the elevated terrain, it forms a wave on the downwind side. These atmospheric waves, called mountain waves or standing waves, are the source of lenticular cloud formation. As the wave rises, the warm, moist air condenses into water droplets, forming a cloud. As the wave then descends, the moisture evaporates back into water vapor and the cloud disappears. These clouds are like a conveyor belt, flowing in the direction of the airstream, while remaining fairly stationary in terms of geographic location. A new cloud forms on the leading edge, moves toward the trailing edge, and then dissipates.

Types of Lenticular Clouds

• Lenticular clouds are broken down into three types: altocumulus standing lenticularis, stratocumulus standing lenticularis and cirrocumulus standing lenticularis. Often, the airstream will produce a series of diminishing waves, creating a string of lenticular clouds. Furthermore, multiple waves can form at different atmospheric levels, producing layered lenticular clouds that are stacked on top of each other. In addition to the lenticular cloud itself, a rotor cloud can also form. These clouds develop below the waves, caused by atmospheric eddies.

Location of Lenticular Clouds

• Lenticular clouds can form anywhere there is rugged terrain; however, the largest and most complex lenticular clouds form over large mountain ranges, such as the Himalayas, Andes and Rocky Mountains. These clouds form perpendicular to the direction of the wind, along the crest of the atmospheric waves. While the airstream is moving at a high rate of speed, the lenticular cloud will remain fairly stationary, riding the peak, or crest, of the wave, much like a surfer. Lenticular clouds generally form between 6,500 and 16,500 feet, depending on the height of the terrain.

Dangers of Lenticular Clouds

• While lenticular clouds can indicate high surface winds, the greatest danger is to pilots flying in the mountainous regions where they form. These clouds provide a visual warning to pilots, indicating the presence of mountain waves. These waves produce wind-shear, a rapid change in the vertical motion of the atmosphere, and turbulence. Pilots flying through these waves can experience strong updrafts on the leading edge of the wave, followed by strong downdrafts on the trailing edge of the wave. The most dangerous area is the swirling and turbulent eddy that forms below the lenticular cloud, in the rotor area. Pilots avoid these areas like the plague.