Virgae

On the Trail with Museum Scientist, Michael W. Nickell

Published Jul 23rd 2019 in Habitats


On the morning of Saturday, April 27, 2019 as I was arriving at Sibley Nature Center for our annual Nature Festival, I saw to the north an altocumulus cloud with some very impressive shafts of virgae. Altocumulus clouds are characterized by globular masses or rolls occurring in layers or patches. Altocumulus is a middle-altitude cloud genus generally forming between 2,000 and 6,100 m (6,600 – 20,000 ft) above ground level. Altocumulus clouds signify convection, or the transfer of heat, due to bulk movement of molecules within the atmosphere. Altocumulus clouds often produce virga (virgae, plural), the streaks or shafts of falling precipitation evaporating before reaching the ground. Virgae can affect the weather as liquid (Virga of higher altitude altocumulus clouds are formed of ice crystals). Virgae can also assist in seeding storm cells. Small particles from one cloud are blown into nearby areas of supersaturated air and act as nucleation particles to build a storm cell. I wish to thank meteorologist and Weather Director, Craig Steward of CBS7, for the identification of the altocumulus cloud.