This mixing would take the form of mammatus clouds.

True to their ominous appearance, mammatus clouds are often harbingers of a coming storm or other extreme weather system.

Gravity waves are proposed to be the formation mechanism of linearly organized mammatus clouds.

Stratocumulus Mamma is a type of mammatus cloud.

This plenitude of proposed formation mechanisms shows, if nothing else, that the mammatus cloud is generally poorly understood.

Therefore, this method does not explain the prevalence of mammatus clouds in one part of the anvil versus another.

The video shows various people and a dog witness in awe, staring at a swirling mammatus cloud formation associated with a squall line.

A picture of mammatus clouds posted to Twitter by meteorologist Jeff Last.

The bobbly clouds that make this image so startling are called mammatus clouds - a name derived from the Latin word for breast.

Cumulonimbus clouds sometimes form mammatus clouds.

Mammatus clouds move over the Fredericksburg Agricultural Fair after a round of thunderstorms passed through the area on Thursday, Aug.

Hail larger than a one pence coin (20mm diameter) was reported in Somerset, and mammatus cloud on the south coast of England in Bognor Regis.

Unusual Mammatus clouds form in the sky over Iron Mountain, Wisconsin in this photo posted to Facebook by Joe Nottage.

Mammatus clouds, as smoothly pebbled as a low-water beach, clung to the underside of thunderheads while pileus clouds - the name means skullcap - clung to their tops.

Weathermen said the mammatus clouds - that appear as lobe-like clusters packed full of ice and rain - were created by thunderstorms that drenched much of the UK on Saturday.

The existence of many different types of mammatus clouds, each with distinct properties and occurring in distinct environments, has given rise to multiple hypothesized formation mechanisms, which are also relevant to other cloud forms.

In storms, air moves in rapid "up draughts" and "down draughts" and mammatus clouds are essentially pockets of air and water droplets which have descended in downward draughts, he says.

Graeme Anderson, a meteorologist, did a thesis on the conditions that cause undulatus asperatus to form, concluding that they were similar to mammatus clouds but with high-level winds shaping the vapour into billowing swirls.

One environmental trend is shared by all of the formation mechanisms hypothesized for mammatus clouds: sharp gradients in temperature, moisture and momentum (wind shear) across the anvil cloud/sub-cloud air boundary, which strongly influence interactions therein.