#cloud identification

CUMULUS | CLOUD IDENTIFICATION

High-level clouds (5-13 km): cirrocumulus, cirrus, and cirrostratus.

CIRRUS

Cirrus clouds are transparent or wispy curls or filaments of cloud floating high in the sky.

This type of cloud is always made of ice crystals whose degree of separation determines how transparent the cirrus is. Besides the filament appearance, cirrus clouds stand out among other types of cloud because they’re often colored in bright yellow or red before sunrise and after sunset, respectively.

Cirrus clouds generally occur in fair weather, but they can also hearld the leading edge of a far-away storm or may mark the edge of a storm passing to the north.

They commonly point in the direction of the air movement at their elevation.

CIRROCUMULUS

These usually form at about 5 km above the surface with small white fluff patterns that spread out for miles and miles over the sky. They’re sometimes called ‘mackerel skies’ because they can sometimes have a grayish color which makes the clouds look a bit like fish scales.

Cirrocumulus clouds exhibit features from both cumulus and cirrus clouds but should not be confused with altocumulus clouds. While the two can look similar, cirrocumulus does not have shading and some parts of altocumulus are darker than the rest. Cirrocumulus cloud comes after cirrus cloud during warm frontal system.

What’s worth keeping in mind about cirrocumulus clouds is that they never generate rainfall (but can mean cold weather) nor do they interact with other types of clouds to form larger cloud structures.

CIRROSTRATUS

Cirrostratus clouds have a sheet-like appearance that can look like a curly blanket covering the sky. They’re quite translucent which makes it easy for the sun or the moon to peer through. Their color varies from light gray to white and the fibrous bands can vary widely in thickness. Purely white cirrostratus clouds signify these have stored misture, indicating the presence of a warm frontal system.

Some of the best cloud pictures involve cirrostratus clouds because the ice crystals beautifully refract light from the sun or moon producing a dazzling halo effect. Cirrostratus clouds can turn into altostratus clouds if these descend to a lower altitude.

As a nice piece of trivia, cirrostratus clouds almost always move in a westerly direction. The sight of them usually means rainfall is imminent in the next 24 hours.

Mid-level clouds (2-7 km): altocumulus, altostratus, and nimbostratus.

ALTOCUMULUS:

Altoculumus clouds are sometimes called ‘social clouds’ because they appear in groups. They have a grayish-white color with some portions darker than the others. 

Altocumulus clouds form at a lower altitude so they’re largely made of water droplets though they may retain ice crystals when forming higher up.  They usually appear between lower stratus clouds and higher cirrus clouds, and normally precede altostratus when a warm frontal system is advancing. When altocumulus appears with another cloud type at the same time, storm normally follows. Altocumulus clouds are common in most parts of the world.

Altocumulus clouds are quite common in most parts of the globe. They usually grow by convection, in most cases after damp air rises to mix with descending dry air. Altocumulus clouds may also form in combination with other types of clouds like cumulonimbus. The amount of rainfall from altocumulus is projected from light to moderate.

ALTOSTRATUS

Altostratus often spread over thousands of square miles and are strongly linked to light rain or snow. Though they’re not capable of yielding heavy rain it’s common for altostratus clouds to morph into nimbostratus clouds which are packed with moisture and can deliver a pounding.

They’re uniformly gray, smooth, and mostly featureless which is why they’re sometimes called ‘boring clouds’. You’ll commonly see this types of clouds in an advancing warm frontal system, preceding nimbostratus clouds.

NIMBOSTRATUS:

The name Nimbostratus comes from the Latin words nimbus which means “rain” and stratus for “spread out”. These gloomy clouds are the heavy rain bearers out there forming thick and dark layers of clouds that can completely block out the sun. Though they belong to the middle-level category, they may sometimes descend to lower altitudes.

Nimbostratus clouds form as a result of the gradual accumulation of moist area over a large area as the warm frontal system lifts the warm and moist area higher up in the atmosphere where it condenses. As outlined earlier, a nimbostratus cloud can form from other types of clouds, like a descending altostratus. Spreading cumulonimbus clouds may also lead to the formation of nimbostratus.

When a stratus cloud (below) produces precipitation it is called a nimbostratus cloud. Dark, heavy nimbostratus clouds can drop steady rain for hours.

Low-level clouds (0-2 km): stratus, cumulus, cumulonimbus, and stratocumulus.

STRATUS:

Stratus clouds are dull, flat, heavy horizontal clouds that lay low in the sky. They are commonly gray but can be white.

Stratus clouds often bring a drizzle or they can bring snow.

The altitude of stratus clouds indicate how fast a storm is approaching. Low stratus clouds usually mean rain will begin soon.

Stratus clouds appear as a hazy veil. They are featureless and depressing. Sometimes they are called “high fog.” They always obscure the sun.

The word “stratus” comes from the Latin prefix “strato-“, meaning “layer”.

Stratus clouds often linger for days as prolonged cloudy weather.

CUMULUS:

‘Cumulus’ is Latin for ‘heap’.

Cumulus clouds commonly indicate fair weather, though they may discharge rains sometimes in form of a light shower. Cumulus clouds are often seen on bright summer days.

Cumulus clouds are flat at the bottom and billowy above.

They are formed by a mass of unstable air, usually air warmed at the ground that is rising. As the warm air rises from the earth—often the air is rising from a patch of bare ground heated by the sun–it cools and the vapor in the rising air condenses into the visible cumulus cloud.

Think of each cumulus cloud as the top of a column of rising air.

The flat bottom of the cumulus cloud indicates the altitude at which the rising vapor has cooled to the point of condensation. Cumulus clouds commonly appear at 3,000 to 6,000 feet (914-1,828 m) but can form and rise higher.

CUMULONIMBUS

The cloud that produces showers and thunderstorms. 

When cumulus congestus clouds produce rain they are called cumulonimbus clouds. Cumulonimbus clouds often form flat, anvil-like tops. These are known as thunderheads and usually bring rain, thunder, and lightning.

It’s a vertical developing type of cloud whose base grows from one to up to eight kilometers, hence it’s commonly called a tower cloud. For the same reason, cumulonimbus is both a low-level and high-level type of cloud. At the low-altitude base, the cloud is mostly made of water droplets but the high-altitude summit is dominated by ice crystals.

The rain comes and goes with this cloud but when it does, it can come pouring. When you see a cumulonimbus, you know there’s a thunderstorm waiting to happen somewhere.

STRATOCUMULUS:

When an accumulation of warm air breaks through a higher mass of cool air it can billow up to form a stratocumulus cloud. 

Stratocumulus clouds are low-lying clouds that have a wide horizontal structure.

Stratocumulus looks like a thick white blanket of stretched out cotton. They resemble cumulus clouds except they’re far bigger. The base is well-defined and flat but the upper part of the cloud is ragged due to convection with the cloud itself.  Depending on the thickness of the cloud, a stratocumulus will have light to dark gray hues.

People often think rain is imminent when they see these clouds. In reality, you’ll be lucky to get a light drizzle out of them.

CLOUD SPECIES & VARIETIES

All of the above represents a broad classification as each type of cloud can be further grouped by species and varieties. The varieties are grouped and named based upon transparency and the arrangement of cloud elements, like so: