Clouds are formed when warm air rises and water vapor condenses into clusters of water droplets. This condensation occurs at a specific temperature, so when conditions are stable, clouds are formed at a specific height, creating a flat layer. Near a thunderstorm, however, turbulent air causes pockets of water and ice to develop, resulting in these bumpy mammatus clouds (think “mammary clouds”).
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Mammatus clouds

Mammatus clouds are some of the most unusual and distinctive clouds formations with a series of bulges or pouches emerging through the base of the cloud. These clouds do not produce severe weather. However, they are associated with big towering cumulonimbus clouds because they are usually found on the underside of an anvil cloud. The reason some people think Mammatus clouds mean severe weather is coming, is because they often appear before a strong storm moves in.

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Photo credit: ©Brett Nickeson | Nebraska, US (2011)


Mammatus Clouds are pouch-like clouds that protrude down from the bottom of a thunderstorm’s anvil cloud. They often form on the underside of cumulonimbus clouds, but are sometimes seen underneath other clouds as well. They can appear threatening, but the sinking air required to make these clouds actually indicates weakening of the storm associated with them.

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NASA Astronomy Picture of the Day 2015 October 18 

Mammatus Clouds Over Saskatchewan 

Why is this cloud so bubbly? Normally, cloud bottoms are flat. The flatness is caused by moist warm air that rises and cools and so condenses into water droplets at a specific temperature, which usually corresponds to a very specific height. As water droplets grow, an opaque cloud forms. Under some conditions, however, cloud pockets can develop that contain large droplets of water or ice that fall into clear air as they evaporate. Such pockets may occur in turbulent air near a thunderstorm. Resulting mammatus clouds can appear especially dramatic if sunlit from the side. These mammatus clouds were photographed over Regina, Saskatchewan, Canada during the summer of 2012.

Mammatus clouds | ©jedimind0421  (Chicago, Illinois, US)

Mammatus clouds are an intriguing enigma of atmospheric fluid dynamics and cloud physics. Most commonly observed on the underside of cumulonimbus anvils, mammatus also occur on the underside of cirrus, cirrocumulus, altocumulus, altostratus, and stratocumulus, as well as in contrails from jet aircraft and pyrocumulus ash clouds from volcanic eruptions.

A variety of mechanisms have been proposed for mammatus formation. Unfortunately, the serendipitous and limited observations of mammatus often lack the necessary thermodynamic and microphysical data to assess their formation and evolution, let alone adequately describe their structure.

Reference: [1]


a rare display of nacreous clouds was seen this week over scotland. nacreous clouds form high in the stratosphere where, given the curvature of the planet, they are illuminated by the sun when below the horizon. the stratosphere is also home to the ozone layer, and these clouds, while beautiful, can lead to the formation of holes in it.    

while it’s usually too cold and dry for clouds to form in the stratosphere, these wispy nacreous clouds develop from a mixture of cooled water and nitric acid, the later of which reacts with cfc compounds released into the environment from industrial processes, causing damage to naturally occurring ozone in the atmosphere.

(click link for credit x, x, x, x, x, x. see also: circumhorizontal arcs, mammatus clouds, noctilucent cloudslenticular cloudsasperatus clouds and more nacreous clouds)