UFO Clouds: What Are Lenticular Clouds?

five layers of lens shaped lenticular clouds over a snowy mountain top

Many people who observed this type of cloud in the winter sky have mistaken it for a UFO. Everyone who has seen these types of clouds has surly thought that nature is playing jokes on the possibility of life outside our planet.

However, this is not the case. These formations in the sky are due to the existence of lenticular clouds. These clouds have the shape of a saucer or converging lens, and they usually appear in mountainous areas.

In this article we are going to tell you what lenticular clouds are. Also, we are going to discuss what conditions should occur in order for them to form and why pilots avoid flying near them.

What Are Lenticular Clouds?

Lenticular cloud formation shaped like an UFO over a city skyline

As already mentioned, this type of clouds have a saucer or UFO shape, and they appear in mountainous areas. The fact that these clouds appear only in mountainous places gives us clues of the conditions required for their formation. Lenticular clouds form in the troposphere, that is, in the lowest layer of the atmosphere.

The characteristics of this cloud are similar to Altocumulus clouds (Ac). Unlike regular altocumulus, it is a standing lenticular cloud (ACSL). Also known as Altocumulus Lenticularis (Ac Len). It can also take the shape of standing lenticular cirrocumulus clouds (CCSL) or standing lenticular stratocumulus clouds (SCSL). These formations depend on environmental and atmospheric conditions such as temperature, wind, atmospheric pressure and humidity.

The most characteristic aspect of these clouds is that they give rise to impressive landscapes and have been confused many times with UFO sightings.

Formation Process

A staggered lenticular cloud formation over a snowy mountain

In order to answer all the questions about the exceptional rarity of these clouds, we need to explain the process of their formation first. The formation of lenticular clouds requires various atmospheric and environmental conditions to occur. The first is a relatively strong upward wind flow which encounters a thermal inversion in the atmosphere. These conditions are more likely to occur in mountain areas, where the air, once it collides with rock formations, is forced to ascend.

Mountains are mechanical obstacles to the flow of air in the atmosphere and thanks to them some events, such as the Foehn Wind occur. As air travels in an upward direction and encounters a thermal inversion, a mechanical turbulence is generated. This is basically friction between the air and the ground. Finally, air with much lower temperature than it was on or near the surface reaches the top.

As it continues to move higher and higher through the atmosphere, the temperature continues to drop further and further due to thermal inversion. If the air that has risen along the mountain is humid, it condenses as temperature decreases at altitude, and reaches the dew point. As the ascending air condenses, a cloud mass that grows to the top of the mountain is formed. Consequently, lenticular clouds are formed due to temperature inversion.

Necessary Weather Conditions

Small lenticular cloud formations that look like UFOs over a lake at dusk

Surely you are thinking that there is always a thermal inversion and that, as we are ascending in altitude, it is colder. Therefore, lenticular clouds should always form. It is true that the upper layers of the atmosphere are generally cooler than the lower ones. These lower layers are fed by the heat that is released from the ground when solar radiation falls on the earth’s surface.

But this is not always the case. There are times when the ground is colder due to a decrease in the amount of sunlight that falls on a surface. It also depends on the color of said surface – darker colors absorb heat while brighter colors reflect it. When the soil is colder, it can absorb all the heat from the surrounding air. This causes the lower layers of air to be at a higher temperature than the upper ones. Given these conditions thermal inversion occurs.

Thermal inversion areas are usually stable over time. In such zones, the air that ascends the mountain slope, is displacing the upper warm air. Then it descends while creating stationary areas that trap condensed moisture and give a cloud its lenticular shape. This is the reason why these clouds look like UFOs and have been mistaken for them numerous times.

Why Avoid Flying Near Lenticular Clouds?

A bell shaped lenticular cloud over a mountainous snowy town

Flight pilots try to avoid flying in the areas near lenticular clouds at all costs. Let’s see why this happens. Since lenticular clouds form when the wind is strong and loaded with moisture, the ascent up the mountain and condensation are very rapid. Having a high stationary layer of thermal inversion makes the wind circulate for a long time in an upward position.

Formations of these clouds can also be found when two opposing air masses collide. As a result, the warmer part rises and the cold air takes the role of mechanical obstacle. The reason why pilots do not want to fly in these areas is because the wind associated with these clouds is very strong. The upward direction of these strong winds can cause serious destabilization in flight.

On the other hand, this type of wind is highly sought after among gliders. Gliding does not require an engine. Instead, air currents are used to plan better and maintain the flight for a longer period of time. A world record for gliding has been achieved thanks to the air currents that give rise to lenticular clouds.


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