Undulatus asperatus

Undulatus asperatus (or alternately, asperatus) is a cloud formation, proposed in 2009 as a separate cloud classification by the founder of the Cloud Appreciation Society, Gavin Pretor-Pinney. If successful it will be the first cloud formation added since cirrus intortus in 1951 to the International Cloud Atlas of the World Meteorological Organization.

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The cloud looks a little like the surface of the sea on a choppy day, which is why it is called asperatus from the Latin verb ‘aspero’, meaning to make rough. The term was used by Roman poets to describe the sea as it was roughened by the cold north wind.

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 but have also been spotted in the Chicago, England and Scotland. These clouds are not considered a precursor to severe weather, rather appear to form following rain or thunderstorm activity. They looks very stormy, but reports have shown that they tend to break up without actually turning into a storm.

The Royal Meteorological Society issued a statement outlining that a new classification could only be introduced if it were acknowledged by the World Meteorological Organisation in Geneva, who publish a thorough bible of cloud classification, The International Cloud Atlas.

The Royal Meteorological Society is now gathering detailed weather data for the days and locations where the asperatus clouds have been seen in an attempt to understand exactly what is causing them. We will keep you updated and see if the Undulatus achieves the status it deserves!!