Cumulus humilis (Cu hum)
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Cumulus humilis (Cu hum)

Summertime is turning into autumn in central Virginia. This picture was taken in September 2019 on a warm, fair-weather afternoon. No chance of rain in sight. Just a few lingering clouds scattered across the sky.

Summary: The main clouds pictured are examples of a low, puffy clouds that are wider than they’re tall, classified as cumulus humilis (Cu hum).

Cloud Type. When you hear the weather report for the day and you’re expecting mostly sunny skies with some scattered clouds, highs in the low 80s, this is the kind of an afternoon scene you’d expect.

There’s no beating around the bush here. These are the kinds of clouds that you’d draw in grade school. The clouds here are a classic example of fair-weather cumulus clouds.

Cloud Species. When determining the species of a cumulus cloud, know that cumulus clouds can be associated with a total of four cloud species: congestus, fractus, humilis, and mediocris. You can visualize the height progression of cumulus cloud species as such: humilis are wider than they are tall, mediocris are as wide as they are tall, and congestus are taller than they are wide. Fractus are fractured, broken up cumulus shards.

A cloud identification tip while we’re on the subject: the humilis, mediocris, and congestus cloud species are only found as cumulus cloud species. No other cloud type can be classified as these species.

In this instance, the majority of the clouds pictured have a wide base and have no vertical growth, particularly the clouds closer to the horizon. You could make the argument that some of the clouds are of the fractus cloud species, but in this case, it’s totally appropriate to classify these as the humilis cloud species.

Cloud Varieties. Of the nine cloud varieties, cumulus clouds can only be of the radiatus cloud species. The radiatus cloud species are identified as clouds lined up in rows, sometimes referred to cloud streets. But this variety doesn’t apply in this case.

Supplementary Features. Cumulus clouds are associated with five of the eleven total cloud features: arcus (shelf cloud), fluctus (Kelvin-Helmholtz waves), praecipitatio (precipitation) , tuba (funnel cloud), and virga (evaporating rain strips). Inspecting the clouds in the above photo, none of these features apply.

Cloud Accessories & Other Clouds. Cumulus clouds are associated with three accessory clouds: pannus (scud clouds), pileus (cap clouds), and velum (horizontal cloud veil). These three cloud accessories are almost always associated with cumulus congestus clouds, so none of them apply here.

Finally, cumulus clouds have three other clouds associated with the cloud type: cataractagenitus (formed from a waterfall), flammagenitus (formed from a fire), and homogenitus (formed from human activity). None of these classifications apply here either.

That’s it! We determined the cloud classification starting from the cloud type and working our way down through cloud species, varieties, features, and accessories taxonomy. With that, we’ve arrived at our official classification: Cumulus humilis (Cu hum).

A graphical illustration of a cumulus cloud

Cumulus (Cu)

Low, puffy, fair-weather

A graphical illustration of a cumulus humilis cloud

Humilis (hum)

Flattened, wider than it is tall

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