Murus Cloud Feature: Wall Cloud, Cloud Lowering

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Definition: A dark cloud feature that protrudes from a base of a cumulonimbus more popularly known as a wall cloud

Description & Characteristics. Translated from latin meaning wall, the ‘murus’ cloud feature is found only in the cumulonimbus cloud type. No other cloud type besides a cumulonimbus cloud can be paired with a murus cloud feature. Murus, more popularly known as wall clouds, are cloud lowerings forming below the updraft base of a cumulonimbus cloud. The proper cloud classification abbreviation for this cloud type and feature is ‘Cb mur’.

Through wall clouds come in different shapes and sizes, they can all be recognized as an organized cloud lowering from the rain-free base of a larger cumulonimbus and are generally a good sign of a strong updraft and a powerful thunderstorm. Wall clouds are considered areas of interest amongst storm chasers as they’re usually associated with areas where tornadoes can potentially form if the storm is strong enough.

Because both cloud features appear to hang towards the ground, shelf clouds (arcus cloud feature) are sometimes mistaken for murus cloud formations, and vise versa. The best way to tell the difference between the two is to recognize that shelf clouds are found at the leading edge of a thunderstorm, where a wall cloud is a more localized cloud lowering beneath the base of the thunderstorm. It’s uncommon find a cumulonimbus cloud that has both murus and arcus cloud features (it’s usually one or the other).

The murus cloud species isn’t very common. Sometimes they’re paired with tail clouds (cauda cloud feature) and are often accompanied by scud clouds (pannus cloud accessory). If you happen to come across one, keep your eyes peeled and stay safe.

Cumulonimbus murus pannus (Cb mur pan)
Cumulonimbus murus praecipitatio (Cb mur pra)
Cumulonimbus murus (Cb mur)
A photograph of a cumulonimbus murus pannus cloud (Cb mur pan) over a dirt road in eastern Colorado

Murus Cloud Types

The murus cloud feature is only associated with the cumulonimbus cloud type.

A graphical illustration of a cumulonimbus murus cloud

Cumulonimbus (Cb)