As severe thunderstorms become more widespread midweek this week, sights of mammatus clouds will become more commonplace, especially associated with the supercell thunderstorms that sometimes produce tornadoes. Sunday evening, there were isolated, supercell thunderstorms that formed late in the day in the Northern Plains, and the National Weather Service in Rapid City, South Dakota were lucky enough to capture the amazing photo below of mammatus clouds, as seen from their often.
These mammatus clouds are not the most common type of clouds, but are often found under the anvil of thunderstorms, especially supercell thunderstorms. This kind of thunderstorm is a discrete, spinning storm and is known for producing large hail, damaging winds, and tornadoes. They are also known for their photogenic displays of amazing clouds, such as the mammatus clouds.
These clouds form due to sinking air in the cloud, often on the backside of a thunderstorm that has passed through. Thunderstorms contain rapidly-rising air, or updrafts, in their center, and once they reach equilibrium where the air can’t rise any further, the air spreads out and that speeding effects allows an anvil to form. These thin anvils can be located over 50,000 feet in altitude, and contain ice crystals and water droplets. Since that saturated air is heavier than the surrounding air, it sinks back down toward the surface. Heat energy is required to evaporate the precipitation particles in this sinking air, but if more energy is required than what is generated by the subsidence, the sinking air will be allowed to sink down even farther because it is cooler than the surrounding air. This subsiding air will eventually allow for the formation of rounded pouch-like structures, which are known as mammatus clouds, under the cloud base. Once the water droplets in the clouds evaporate, these mammatus clouds will disappear but can last for several hours before this happens.