Cloud types and what they mean for pilots

Cloud types

It is important for pilots to have a good knowledge of meteorology and existing weather conditions. Cloud formations will give pilots a clear indication of the weather.

So it’s important to know how to identify the various types. To help you become a meteorological expert, we’ve picked 3 important cloud types to understand.

  1. Low-level clouds (cumulus, stratus, stratocumulus) that lie below 6,500 feet (1,981 m)
  2. Middle clouds (altocumulus, nimbostratus, altostratus) that form between 6,500 and 20,000 feet (1981–6,096 m)
  3. High-level clouds (cirrus, cirrocumulus, cirrostratus) that form above 20,000 feet (6,096 m)

1. HIGH-LEVEL CLOUD

The high-level cloud refers to clouds with a base above 20,000 feet. There are three important high-level clouds to watch out for.

  • Cirrus – a thin fibrous cloud.
  • Cirrocumulus – a thin granular layer of small lumps of cloud.
  • Cirrostratus – a thin uniform cover of cloud.

These cloud types vary in thickness and the sun can easily be observed through all three, with only the intensity of light varies. These clouds can consist of several thin layers.

Cloud types

Cirrus

Like their name suggests (which is Latin for “curl of hair”), cirrus are thin, white, wispy strands of clouds that streak across the sky. Because cirrus clouds appear above 20,000 feet (6,096 m)—an altitude where low temperatures and low water vapor exist—they are made up of tiny ice crystals rather than water droplets.

Cirrus typically occur in fair weather. They can also form out ahead of warm fronts and large-scale storms like nor’easters and tropical cyclones, so seeing them can also indicate storms may become.

NASA’s Earthdata site quotes a proverb that sailors learned to warn them of coming rainy weather, “Mares’ tails (cirrus) and mackerel scales (altocumulus) make lofty ships to carry low sails.”

Cirrocumulus

Cirrocumulus clouds are small, white patches of clouds often arranged in rows that live at high altitudes and are made of ice crystals. Called “cloudlets,” the individual cloud mounds of cirrocumulus are much smaller than that of altocumulus and stratocumulus and often look like grains.

Cirrocumulus clouds are rare and relatively short-lived, but you’ll see them in winter or when it’s cold but fair.

Cirrostratus

Cirrostratus clouds are transparent, whitish clouds that veil or cover nearly the entire sky. A dead giveaway to distinguishing cirrostratus is to look for a “halo” (a ring or circle of light) around the sun or moon.

The halo is formed by the refraction of the light on the ice crystals in the clouds, similar to how sundogs form but in an entire circle rather than just on either side of the sun.

Cirrostratus indicate that a large amount of moisture is present in the upper atmosphere. They’re also generally associated with approaching warm fronts.

2. MID-LEVEL CLOUDS

If you think of clouds as cake layers, a mid-level cloud is the medium layer of chocolate filling. This set of cloud types has a base above about 6,500 feet. Developing in the middle layers of the atmosphere, they are much brighter and less fragmented in appearance.

The fragmented appearance occurs due to their distance from the ground and their higher composition of ice crystals. There are two important mid-level clouds to watch out for. Altocumulus – a thin layer of lumps of heaps of cloud, and altostratus – a thin uniform layer of cloud.

These middle-level clouds vary in thickness from flat sheets to a cumuliform appearance and tend to move slower than lower-level clouds, in the direction of the wind at that level, usually a different direction to surface winds.

Cloud types

Altocumulus

Altocumulus clouds are the most common clouds in the middle atmosphere. You’ll recognize them as white or gray patches that dot the sky in large, rounded masses or clouds that are aligned in parallel bands. They look like the wool of sheep or scales of mackerel fish—hence their nicknames “sheep backs” and “mackerel skies.”

Altocumulus and stratocumulus are often mistaken. Besides altocumulus being higher up in the sky, another way to tell them apart is by the size of their individual cloud mounds. Place your hand up to the sky and in the direction of the cloud; if the mound is the size of your thumb, it’s altocumulus. (If it’s closer to fist-size, it’s probably stratocumulus.)

Altocumulus are often spotted on warm and humid mornings, especially during summer. They can signal thunderstorms to come later in the day. You may also see them out ahead of cold fronts, in which case they signal the onset of cooler temperatures.

Nimbostratus

Nimbostratus clouds cover the sky in a dark gray layer. They can extend from the low and middle layers of the atmosphere and are thick enough to blot out the sun.

Nimbostratus is the quintessential rain cloud. You’ll see them whenever steady rain or snow is falling (or is forecast to fall) over a widespread area.

Altostratus

Altostratus appears as gray or bluish-gray sheets of cloud that partially or totally cover the sky at mid-levels. Even though they cover the sky, you can typically still see the sun as a dimly lit disk behind them, but not enough light shines through to cast shadows on the ground.

Altostratus tends to form ahead of a warm or occluded front. They can also occur together with cumulus at a cold front.

3. LOW-LEVEL CLOUDS

The low-level cloud refers to clouds with a base below about 6,500 feet. Developing in the lower level of the atmosphere, these clouds vary in shapes and sizes. There are five important clouds to watch out for.

Nimbostratus – a thick layer of rain-bearing cloud. Stratocumulus – a layer of relatively small lumps and heaps of cloud. Stratus – a layer of uniform cloud. Cumulus – cumuliform clouds, and cumulonimbus – thunderstorms!

These clouds are of most interest to pilots and controllers as they cause the most impact on safe flying conditions, particularly with regard to poor visibility, turbulence and structural damage, icing, and runway contamination.

Knowing the difference between cloud types is very important when it comes to aviation. More in-depth research on types of cloud will strengthen your meteorological knowledge and help you become a better pilot.

If you found this blog interesting, why not check out how to handle a radio failure mid-flight

Cloud types

Cirrus

Like their name suggests (which is Latin for “curl of hair”), cirrus are thin, white, wispy strands of clouds that streak across the sky. Because cirrus clouds appear above 20,000 feet (6,096 m)—an altitude where low temperatures and low water vapor exist—they are made up of tiny ice crystals rather than water droplets.

Cirrus typically occur in fair weather. They can also form out ahead of warm fronts and large-scale storms like nor’easters and tropical cyclones, so seeing them can also indicate storms may become.

NASA‘s Earthdata site quotes a proverb that sailors learned to warn them of coming rainy weather, “Mares’ tails (cirrus) and mackerel scales (altocumulus) make lofty ships to carry low sails.”

Cirrocumulus

Cirrocumulus clouds are small, white patches of clouds often arranged in rows that live at high altitudes and are made of ice crystals. Called “cloudlets,” the individual cloud mounds of cirrocumulus are much smaller than that of altocumulus and stratocumulus and often look like grains.

Cirrocumulus clouds are rare and relatively short-lived, but you’ll see them in winter or when it’s cold but fair.

Cirrostratus

Cirrostratus clouds are transparent, whitish clouds that veil or cover nearly the entire sky. A dead giveaway to distinguishing cirrostratus is to look for a “halo” (a ring or circle of light) around the sun or moon.

The halo is formed by the refraction of the light on the ice crystals in the clouds, similar to how sundogs form but in an entire circle rather than just on either side of the sun.

Cirrostratus indicate that a large amount of moisture is present in the upper atmosphere. They’re also generally associated with approaching warm fronts.

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