On watch in my favorite cloudspotting hammock over the weekend, these strange clouds covered a patch of the sky. Judging by their height, I figured they were cirrus, but couldn't figure out what variety. I grabbed The Cloud Collector's Handbook, by Gavin Pretor-Pinney and flipped through it--quickly for what I hoped would be an instant match between sky and page. I found it under lacunosus. "This variety of cloud is identified in terms of the gaps between cloud elements, rather than the clouds themselves," Pretor-Pinney writes. "It is when a cloud layer is composed of more or less regular holes, around which fringes of cloud form, like a net or rough honeycomb."
So the cloud pictured here is a cirrocumulus undulatus lacunosus. These cirrus because they are high-elevation clouds formed of ice crystals; cumulus because they appear in patches or layers of cloudlets (not wisps like plain cirrus); undulatus because they appear in waves which form when the air above and below the cloud layer is moving at different speeds or in different directions; and lacunosus because of the holes formed by sinking pockets of air.
Apparently, this variety of cloud is short-lived (and earns bonus points on the cloudspotter's scorecard). In fact, about ten minutes after I photographed them, they disappeared.
While collecting points for spotting clouds is geeky, it was oddly gratifying to be able to name clouds I would have described as "white" a year ago.