mammatus clouds from UCARWhile Gothamist is sure most everybody noticed the cumulonimbus cloud that so drenched Leslie last evening, we wonder if anyone else saw the mammatus clouds around sunset. Mammatus clouds are so named because they are shaped like breasts. If you google for mammatus, or read their descriptions in introductory meteorology textbooks you will discovery the many ways authors avoid making an analogy with the horribly offensive b-word.

Clouds were named by Luke Howard, an amateur British weather enthusiast who would have felt quite at home on Gothamist Weather, in the early 19th century. With only minor changes, his naming convention is still used today. Howard's insight into naming clouds was twofold. First, he recognized that most clouds fit into one of four types, and that those types were related to how those clouds were being formed. Second, Howard gave the clouds Latin names. Howard was familiar with the Linnean scheme of naming plants and animals and realized that giving Latin names to clouds would, like the clouds themselves, would transcend national and language borders.

The cloud categories are:

Cumulus for heaps of clouds,
Stratus for layered clouds,
Cirrus for high, wispy, fibrous clouds, and
Nimbus clouds from which precipitation falls

The cloud names can be combined, hence cumulonimbus are big heaping clouds that produce rain.

What about mammatus clouds? Mammatus are one of the few types of clouds that don't fit into any of Howard's categories. Clouds typically form when air rises, cools, and reaches saturation. Mammatus most frequently form as cold saturated air sinks on the underside of a cumulonimbus. The saturated air warms as it sinks, the liquid evaporates and the ice particles melt in characteristically rounded shapes.