Clouds of the Day - Mammatus

Mammatus Photo Copyright 2016 by Craig Johnson, Weather Briefing, LC

Mammatus clouds create dramatic patterns across the sky. Mammatus frighten many people because of their ominous look and relative rarity. From below the clouds appear dense but they are transparent when viewed from the cloud level. They are caused when heat released by condensation in thunderstorm updrafts reaches the stable layer of air at the top of the storm. The updraft slows and eventually sinks and rises and falls like a cork on waves in a lake. The up and down motion gradually dampens out.

The clouds are distinct and include waves and pouches that protrude down from the underside of the thunderstorm anvil. The clouds are not dangerous to us on the ground but the dramatic patterns of the clouds are often found with strong to severe thunderstorms. The coloration is due to light from the setting Sun shining on the underside of the clouds.

In this photo the mammatus are in the higher of the two cloud layers. The lower layer with the dark bases are altocumulus clouds. Mammatus are most often visible through the clear air on the back side of the anvil. They can appear elsewhere under the anvil but are often hidden by lower clouds and rain.