Undulatus asperatus (or alternately, asperatus) is a rare, newly recognized cloud formation, that was proposed in 2009 as the first cloud formation added to the International Cloud Atlas of the World Meteorological Organization since cirrus intortus was added in 1951. The name translates approximately as "roughened or agitated waves". Although they appear dark and storm-like, the clouds tend to dissipate without a storm forming. The ominous-looking clouds have been particularly common in the Plains states of the United States, often during the morning or midday hours following convective thunderstorm activity. As of June 2009, the Royal Meteorological Society is gathering evidence of the type of weather patterns in which undulatus asperatus clouds appear, so as to study how they form and decide whether they are distinct from other undulatus clouds.
Click here to view pictures taken of the clouds on June 7th.
Do you want to learn more about clouds?
- The cloudspotter's guide : the science, history, and culture of clouds by Gavin Pretor-Pinney ; chapter illustrations by Bill Sanderson.
- Instant weather forecasting : a 24-colour photograph guide to weather forecasting from the clouds by Alan Watts.
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