Mammatus clouds in Porto Alegre before the arrival of the cold front

Mammatus-type clouds could be observed and were photographed by MetSul Meteorologia in the early afternoon of this Saturday in Porto Alegre. The clouds were in the northern sector of the capital of Rio Grande do Sul, which has had a day so far with lots of clouds and muggy weather before the arrival of the rain, which is expected later today.

Mammmatus clouds are rarer in winter and usually appear in the warm period of the year between spring and early autumn, especially in summer. This type of cloud is commonly associated with clouds of great vertical development formed by heat and humidity that bring convection, that is, the upward movement of air that generates clouds of great vertical development of thunderstorms.

The term “Mammatus” derives from the word “mamma” due to its association with the shape of breasts or breasts. They are formed by descending air, in contrast to most clouds that are generated by ascending air currents.

This type of cloudiness tends to occur more frequently under the anvil associated with a Cumulonimbus cloud (Cb) and is generally observed after the passage of a severe storm. This was not the case earlier this afternoon, when there was neither a storm nor a huge cloud of the Cb type, although vertically developing clouds of the convective type were observed.

There are several documented cases of spectacular appearances of Mammatus, such as in November 2021 in Argentina. As a rule, Mammatus appear at the bottom of a thundercloud, however they can also be seen next to other types of clouds.

They have been observed in the upper, middle and lower atmosphere associated with Stratocumulus, Altocumulus, Altostratus, Cirrus and Cirrocumulus. In exceptional cases, Mammatus can occur in “condensation trails” generated by airplanes in the sky and even in volcanic dust clouds.

Here’s a tip! If you see Mammatus clouds in the sky, don’t be alarmed. Despite the appearance that is frightening and impressive at the same time, when they appear in the sky it is an indication that the storm with which they are associated, when present in a storm, is in the process of weakening.

But today’s Mammatus clouds cannot be interpreted as a sign that the instability has passed or is abating. On the contrary, a cold front is advancing from the south of the state and will bring rain over the next few hours to the capital region. There is even a risk of storms in the next few hours and heavy rain later this Saturday, especially between tonight and early Sunday.

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