Finger clouds are a descriptive term for certain cloud formations that resemble fingers extending downwards from a larger cloud mass. These aren't a formally classified cloud type in meteorology, but rather a visual description applied to various types depending on their appearance. The "fingers" are typically formed by downdrafts within the cloud, causing parts of it to descend and create this unique, finger-like structure.
Types of Clouds that Can Appear as "Finger Clouds":
Several cloud types can exhibit this finger-like appearance:
- Altocumulus: These mid-level clouds sometimes form patches with distinct, finger-like protrusions. If the cloud mound is about the size of your thumb held at arm's length, it might be altocumulus. A photo example showing this finger-like appearance in Altocumulus clouds can be found at https://epod.usra.edu/blog/2011/09/cloud-fingers-over-tracy-california.html.
- Cirrocumulus: While less common, cirrocumulus clouds, which are high-altitude clouds, can also appear with small, finger-like features. These cloudlets are much smaller, approximately the width of a pinky finger held at arm's length.
The appearance of "fingers" is related to atmospheric dynamics, specifically downdrafts within the cloud. As noted in https://slate.com/technology/2014/04/weird-clouds-downdraft-causes-cloud-fingers-to-descend.html, these descending fingers are a clear result of downdrafts within the cloud mass.
