#2376 "Singleton Mammatus"

The heavy rain and strong winds painted in #2375 "Fire and Rain Coming" had swept south of Singleton. The time of that painting was 2:30 pm on Saturday June 6th. This view of the back side of the thunderstorm under the anvil was from an hour later.

The mammatus was more dramatic than what I usually see associated with most storms. Mammatus clouds certainly do look ominous and they do have a story to tell. Here is that tale.

Mammatus cloud are also called simply mamma or mammatocumulus. They are cellular pouches that hang under the base of a cloud. Typically this cloud is the anvil of a thunderstorm also known as a cumulonimbus. Mammatus result from the sinking of moist air into dry air. Some people think of mammatus as upside-down clouds.

Mammatus are rare for clouds in that they actually are sinking in the atmosphere. Most clouds are formed in ascending air. The pouches of cloud must be cooler than the surrounding air in order to descend in the atmosphere. The longest living and thus dramatic mammatus clouds like those I painted are comprised of large drops and snow crystals. These larger particles require greater amounts of energy for evaporation into oblivion to occur. The water droplets or snow flakes warm as they fall into higher pressures within the cold mammatus pouch. Simultaneously, the smaller particles will get to a point were they will evapourate or sublimate into water vapour. This vapourization process takes energy and cools the air in the descending pouch. The balance of subsidence warming and evapourative cooling means that these descending pouches of droplets or flakes will sink slowly. They will continue to do so but at a slower rate until the particles are all turned into water vapour and the mammatus cloud is no more.

Mammatus clouds are not an indication of severe weather or tornadoes. Thunderstorms do send moisture aloft into their anvil and the stronger the updraft, the more moisture will comprise that shelf of cloud aloft. What goes up must also come down. Large particles dropping into dry air are the mammatus pouches coming down. They are beautiful and to correspond typically with a strong thunderstorm updraft but that storm is not necessarily severe. Supercell thunderstorms are the severe type of convection and they also require the ingredient of wind shear but we will not get into that today.

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