Cirrocumulus lacunosus in the early morning of 1 Aug 2014 (Jerry Tangren, East Wenatchee, WA)
Cirrocumulus clouds occur high in the sky, typically short-lived as the ice crystals that comprise them are carried away in the strong upper-level winds. Even more fleeting is the variety of these clouds referred to as lacunosus. This word is Latin for “full of holes” and is commonly referred to as appearing like a honeycomb.
The American Meteorology Society’s glossary defines this cloud variety as follows:
A cloud variety characterized more by the appearance of the spaces between the cloud elements than by the elements themselves.The gaps are generally rounded and often have fringed edges. The overall appearance is that of a honeycomb or net, the negative of that of clouds composed of separate rounded elements. This variety is a modification mainly of the genera cirrocumulus and altocumulus and may apply to the species stratiformis, castellanus, or floccus.
How do these form? The holes indicate areas of sinking air, while the fringed edges indicate localized areas of compensating rising motion. This can happen when a layer of colder air moves over warmer air. The cold air is more dense, creating those pockets of sinking motion. This process is relatively quick so it’s rare to see this pattern persist for very long.
Cirrocumulus are a high-level cloud (found at altitudes above 16,000 ft) that, similar to other cumuliform types of clouds, indicate instability. These consist of small amounts of liquid water that are supercooled, meaning they exist in liquid form at temperatures below freezing. Ice crystals are also present, which cause the supercooled drops to freeze and change the cirrocumulus into cirrostratus.
Here is an example of this transition from April 2013 over Seattle. You can still make out some of the individual cloud elements (the cirrocumulus), but overall, they are less defined and becoming more stratified/spread out.
Location: Seattle, Washington
Date: April 2013