Extraordinary weather phenomenon: mammatus

When the weather is stormy, hundreds of cloud globes can appear in the sky for a few minutes. Mammatus are spectacular clouds that can easily be seen if you scan the sky at the right time.

The appearance of these strange protuberances often testifies to a stormy weatherbut despite their apocalyptic appearance, mammatus do not necessarily indicate the arrival of phenomena weather report dangerous. Their name comes from the Latin word ” mom “, which unsurprisingly means “udder” or even “breast”. Each of these globes measures 1 to 2 km in diameter and they appear under another cloud: they are therefore not a cloud in their own right, but an extension of clouds of the cumulonimbus, stratocumulus, altostratusaltocumulus, cirrocumulus and more rarely cirrus. Some have also been observed under the volcanic ash clouds.

The mammatus, upside-down clouds

The mammatus are formed during the dive of theair moist in dry air. They are actually “upside down” clouds! In stormy weather, the cumulonimbus is the seat of many ascending and descending currents. The base of the cloud is the limit where the descending air is warm enough to dry out: the juxtaposition of dry areas and waterlogged areas produces a globe whose center is a downdraft. The droplets or ice crystals of the cloud evaporate down into the dry layer. This movement is at the origin of the creation of these air pockets in the shape of breasts. Mammatus generally form in the part of the cloud farthest from the active zone of precipitation. So there is no precipitation under the mammatus, but this area is subject to strong upper winds and aircraft generally prefer to avoid it.

A spectacular phenomenon during sunsets

Mammatus clouds are actually quite common, and can be observed very regularly all over the world. In France, they are frequent during stormy degradations in spring and summer. Most mammatus are unremarkable in appearance and often go unnoticed by eyes of a neophyte. However, these globes, which are originally gray like the cloud they belong toare particularly spectacular when the Sun is low on the horizon: at sunrises and sunsets, the mammatus are illuminated in red, purple or orange, and give rise to grandiose skies.

The most incredible mammatus are observed in regions of the world with thunderstorms the most violent: in the United States during the season thunderstorms and tornadoes, Australia, South America and Italy. Most of the time, the appearance of mammatus, which you observe, indicates that the storm has already passed over you, because these globes often form behind a mature cumulonimbus.