FROM APOD (via Nick Doak)

Asperatus Clouds Over New Zealand
Image Credit & Copyright: Witta Priester

Known informally as Undulatus asperatus clouds, they can be stunning in appearance, unusual in occurrence, are relatively unstudied, and have even been suggested as a new type of cloud. [...] The above image, taken above Hanmer Springs in Canterbury, New Zealand, in 2005, shows great detail partly because sunlight illuminates the undulating clouds from the side.