Clouds of the Day - Cirrus and Ice Crystals - Sunday, October 22, 2023

All of the clouds in these photos are types of Cirrus clouds with fall streaks - bands of falling ice crystals precipitating from the clouds. The cirrus are in thick clumps (spissatus) that may include both ice crystals and water cloud droplets. As the top of the cirrus precipitate the dense head dissipates leaving only remnants of the original cloud as fibers or thin streamers that appear to be falling out of clear air.

Cirrus spissatus are dense clumps of high clouds usually above 20,000 feet. It has been estimated that about 50% of Cirrus spissatus are formed from the debris of past thunderstorm anvils. The other 50% form when convective rising motion forms dense localized convection at high levels. The convection cloud precipitates ice crystals that look like fibrous streamers. As the streamers persist the clouds gradually dissipate. See the several examples below.

Cirrus spissatus

Cirrus spissatus with fall streaks of ice crystals

Cirrus fibratus

Cirrus spissatus and Cirrus fibratus formed by convection intermingled with fall streaks of ice crystals.

Cirrus spissatus with fall streaks. Note the three birds circling at the left center of the photos. They appeared to be riding a thermal of rising air like gliders.