Altocumulus Undulatus

Above: Altocumulus Undulatus

Altocumulus Undulatus

These clouds form in the mid atmosphere level this is typically from about 8,000 to 20,000 feet, when you observe altocumulus undulatus clouds they appear like a type of white carpet with ridges and valleys that cover a large amount of the sky. Their presence can indicate that you could expect bad weather to be moving in, but this may not happen and the result will only be a cloudy day.

What are altocumulus undulatus clouds?

Altocumulus undulatus are a type of cloud. The genus name, altocumulus, means that these clouds occur at an average altitude above sea level when compared to other clouds. Indeed, the altocumulus undulatus can be found at around 6,000 to 16,000 feet above sea level. These clouds normally contain some sort of precipitation such as water, ice or snow. Most of the time, they release this precipitation. Altocumulus undulatus can therefore be thought of to be predictors of precipitation, but this is not a constant finding. It’s very common to find that the sky has lots of altocumulus undulatus, but it doesn’t mean that it’s going to rain or snow.

Altocumulus undulatus clouds are a mid-level cloud formation that is either white or grey depending upon the clouds thickness. They can appear either as a solid sheet of cloud covering the sky or they can be seen in patches. You will observe that edges of the undulations will seem darker as they are normally thicker than the rest of the cloud formation.

Altocumulus undulatus clouds are normally darker than cirrostratus clouds and they are not as large as stratocumulus clouds. The altocumulus undulatus clouds are not thick; they are typically about 300 feet thick. They look like waves or ripples of water in the sky and they can be turned from pink to purple by the rising or setting sun should it be able to shine on to them from below the horizon.

How are altocumulus undulatus clouds formed?

Altocumulus undulatus clouds are formed just like any other clouds: by condensation of water droplets which is being carried by air. The moisture content in air can be acquired through several methods such as:

•             The air could move over a large water body such as an ocean. In the process of doing this, it could pick up water droplets, which then saturate the air.

•             The heat from the sun could cause water on the surface of the earth to evaporate.

Whatever the means of acquiring the air, what has to happen next is that the air and moisture combination has to be transported to the upper reaches of the atmosphere. In such an environment, the lower temperatures force the moisture within the clouds to condense, which leads to formation of the clouds. The condensation could comprise water in super cooled liquid state, or it could also be in solid form such as ice crystals or even snow.

Altocumulus undulatus clouds are formed by water moisture at ground level being sucked to higher altitudes from between 6,000 to 20,000 feet. The fact that these clouds can form at this level indicates that at the moment they are forming up there is no risk of cumulonimbus clouds forming that could cause a storm or heavy rain burst to occur. However should the cloud continue to expand and thicken, it may be the early warning that bad weather is on its way in normally within 20 hours of them being observed for the first time.

What height are altocumulus undulatus clouds found?

Altocumulus undulatus clouds are a mid-level cloud formation, which means that they can be found normally above 8,000 feet and as high up as 20,000 feet, it is possible that they can be observed with the higher level cirrostratus clouds above them. Should they be observed at higher altitudes, such as 18,000 to 20,000 feet in winter, they will be made up of ice crystals rather than water particles and the altocumulus undulatus clouds will appear a more brilliant white color as the ice crystals reflect the sunlight.

The altocumulus undulatus clouds form at an altitude of 6,000 to 16,000 feet above sea level. This height is normally measured from the base of the cloud to the sea level. Of course, one would expect that these clouds would have considerable height, so finding that the distance from the base to sea level doesn’t mean that you can’t find more cloud above this height.

Classification of altocumulus undulatus clouds

Altocumulus undulatus clouds usually form at an altitude of 6,000 and 16,000 feet, and can thus be termed as middle level clouds.

What do altocumulus undulatus clouds look like?

Altocumulus undulatus clouds normally look like gently rolling waves in the sky. The undulating bases of these clouds normally results from local eddies at the base of the clouds, forming bases which are wave like in pattern.

How common are altocumulus undulatus clouds?

Altocumulus undulatus clouds are able to be seen all year round across the world, you will notice:

  • They are visible all year round


  • They can appear in patches or cover a far wider area, blankets of altocumulus undulatus clouds have been observed over an area of between 100 to 200 miles


  • They indicate a worsening of the weather that will happen within the next 20 hours


These clouds are considered harmless to planes, they are not particularly thick and normally of not more than about 300 feet. In the southern US states they can indicate a tropical airstream moving in, in the western US states they can indicate monsoon airflow is arriving.

Altocumulus undulatus clouds are very common. They usually form and dissipate many times during the day, and this means that if you pay attention you may be able to spot them. Of course, they are more common in areas that have the right kind of humidity, such as in the temperate regions.

Where can I see altocumulus undulatus clouds?

Altocumulus undulatus clouds can be seen in areas which normally have cold air fronts converging with warm moist air, causing the water in the air to condense and form the clouds.

Back to Top