international cloud atlas

International Cloud Atlas & new cloud classifications

On World Meteorological Day (23rd March 2017), the World Meteorological Organization (WMO) released its new, online, digitised International Cloud Atlas, which is the global reference for observing and identifying clouds. It contains a number of new cloud classifications, including the eagerly-awaited asperitas, a dramatic undulated cloud which has captured media interest and public imagination.  The RMetS originally reviewed examples of asperitas  provided by Gavin Pretor-Pinney of the Cloud Appreciation Society. 

New cloud type spotted over Snowdonia

These dramatic clouds are the newest cloud type in over 50 years and were spotted over Snowdonia, UK this weekend. 

Asperitas formations are incredibly rare and look like rough, sea waves in the sky. The base of these clouds is usually between 4,000 - 10,000ft (1 – 3km) and as with all cloud names, they are derived from Latin with aspero meaning ‘roughness’.  At first glance, or when doing research, they may appear to fall into the undulatus clouds category, however they are more chaotic and have less horizontal structure compared to undulatus clouds.