Altostratus opacus (As op)
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Altostratus opacus (As op)

Here’s a photo taken this past weekend (October 2019) in central Virginia. Between the cooling temperatures and changing leaves, it’s really starting to look and feel like autumn.

Summary: This mid-altitude layer is a particularly dark cloud blanket, classifying it as altostratus opacus (As op).

Cloud Type. To start, there’s hardly any detail in this cloud. It’s a flat cloud blanket extending from one horizon to the next. A good description for this cloud would be stratiform, or layerlike. The five clouds that include the latin term strato- are cirrostratus, altostratus, nimbostratus, stratus, and stratocumulus.

We’ve already determined these clouds are without detail. Stratocumulus clouds are low, puffy layer clouds. Let’s cross those off the list. And there’s no rain in sight. Not nimbostratus, either.

Cirrostratus clouds are a high, pale like layer. Sometimes cirrostratus clouds are so thin, they’re difficult to observe. You can always see the sun through a cirrostratus cloud. This cloud is way too dark to be a cirrostratus cloud.

We’re left with stratus and altostratus clouds. Altostratus clouds are higher in altitude compared to stratus clouds. Stratus clouds are low layer clouds, and capable of touching the ground. Fog would be classified as a stratus cloud. These clouds don’t seem very low to the ground. You can see reasonably far into the distance.

We’ve arrived at the cloud type. It’s fair to classify these as an altostratus cloud.

Cloud Species. Altostratus clouds are boring in relation to other cloud types. There aren’t any cloud species associated with altostratus clouds.

Cloud Varieties. Altostratus clouds are associated with five cloud varieties: duplicatus (multilayered), opacus (darkened), radiatus (parallel bands), translucidus (see-through), and undulatus (wavelike or undulating).

The cloud seems like one solid layer, so duplicatus can be crossed off the list. They’re definitely dark, so opacus would apply. The radiatus cloud variety is seldom seen in the altostratus cloud type and we don’t see them here. Translucidus doesn’t apply since we already determined that they’re dark. Finally, there aren’t any significant wavy or undulating features found in this example.

While a cloud can be classified as multiple cloud varieties, the only one that applies is the opacus cloud variety.

Supplementary Features. Altostratus can be associated with three of the eleven cloud features: mamma, precipitatio, and virga. Since there are no mammatus clouds present, no rain, and no virga (evaporating rain strips), there are no features in this case.

Cloud Accessories & Other Clouds. The only other cloud subtype that can be applied to altostratus clouds are pannus, which are scuddy cloud shards. None are present here… so we’re done!

In today’s lesson, the cloud classification was determined with the cloud type and working our way down through its subtypes. The final classification? Altostratus opacus (As op).

A graphical illustration of an altostratus cloud

Altostratus (As)

Mid-altitude gray layer

A graphical illustration of an altostratus opacus cloud

Opacus (op)

Opaque, masks the sun

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