Chicago Asperatus Clouds


Last week we kicked off the Fourth of July weekend with the most extraordinary clouds I’ve ever seen in the city, which were the talk of the Internet around here. In trying to figure out exactly what they were, I learned that the particular formation you see above—notable for looking like the underside of the surface of a rough ocean—was proposed, a couple years ago, as a new cloud variety: asperatus clouds.

There hasn’t been a "new" type of cloud officially recognized by the World Meteorological Organization since 1951 (cirrus intortus) and entered into the International Cloud Atlas, so it’s not something that’s done lightly. I was curious to see how the process was going, so I asked the Royal Meteorological Society what had happened since 2009, when it started looking into asperatus clouds at the suggestion of Gavin Pretor-Pinney of the Cloud Appreciation Society. According to Paul Hardaker, chief executive of the RMS, there seems to be evidence that asperatus clouds are sufficiently distinctive to merit their own variety, and they "hope to make a case for including the new cloud in the next update of the [International Cloud] Atlas, which we hope will be in the next 12 months." So the process isn’t over, but it’s still an impressive development in citizen meteorology.


Photograph: John Picken (CC by 2.0)