Cirrostratus fibratus (Cs fib)
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Cirrostratus fibratus (Cs fib)

It’s the last day of summer in central Virginia. We have an example of a fibrous, high-altitude cloud layer. This cloud layer is particularly thin. Plenty of blue sky can be seen.

Summary: This is an example of a pale, fibrous, high-altitude layer cloud spread across the sky, classified as cirrostratus fibratus (Cs fib).

Cloud Species. Here’s an example of where you might recognize the cloud species before recognizing the cloud type. You can see the cloud is fibrous, particularly in the upper-right hand portion of the photograph. It was difficult to capture the cloud’s entirely in one photograph, but the entire sky beyond what you can see in the picture had these light cloud strands spread almost from one horizon to the next.

Wispy, hairlike, and fibrous are all good adjectives to describe this cloud. This is a great example of the fibratus cloud species.

Cloud Type. Now that we’ve recognized the cloud feature, let’s determine the cloud type. The fibratus cloud species is only found in two high-altitude cloud types: cirrus and cirrostratus.

Cirrus fibratus clouds are usually thicker, individualized cloud strands that look like individual locks of hair. In this case, the entire sky is blanketed with these clouds. The strands are also very light, almost invisible.

Because of the extent of these clouds covering the sky, it’s fair to classify these as the cirrostratus cloud type.

Cloud Varieties. Cirrostratus clouds are only associated with two cloud varieties: duplicatus and undulatus. Duplicatus means there are two layers of cirrostratus clouds found at different altitudes. In our case, it appears the cloud is one fibered, uniform layer. The cloud doesn’t appear to be wavy and undulating either. No need to apply a cloud variety in this case.

Supplementary Features. You’re off the hook! Cirrostratus clouds don’t have any cloud features associated with them.

Cloud Accessories & Other Clouds. The only other kind of cloud classification that can be applied to cirrostratus clouds is the homomutatus classification, which means a cloud that takes on a more natural appearance, but was originally formed by humans.

Sometimes, the condensation trail from an aircraft can remain in the higher levels of the troposphere for hours. Instead of dissipating, they can spread out across the sky, creating a thin cloud layer.

There isn’t any indication that the clouds in the photograph were caused by an aircraft. They seem to be naturally formed. So the homomutatus classification doesn’t apply.

In this example, the cloud classification was determined from recognizing the cloud species first, and working backwards to figuring out the cloud type. Our official classification has been determined: Cirrostratus fibratus (Cs fib).

A graphical illustration of a cirrostratus cloud

Cirrostratus (Cs)

Pale, veil-like layer

A graphical illustration of a cirrostratus fibratus cloud

Fibratus (fib)

Fiberlike, hairlike

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