Asperatus Clouds Form

Asperatus Undulatus: The Wavy Canopy

The choatic, wavy canopy of clouds is known as asperatus undulatus, Latin for "agitated waves."

This cloud species, not yet officially recognized by the World Meteorological Organization, is sometimes seen after a thunderstorm's gust front has passed you. 

Ahead of either a single thunderstorm or line of storms, you may first experience a strong gust of wind, which denotes the gust front.  Look skyward – from a safe place in a thunderstorm, that is – and you may see these undulatus asperatus clouds. 

Similar to lenticular clouds, what you're seeing is turbulent wave motion. According to Graeme Anderson, from the Department of Meteorology at Reading University, winds at cloud level lead to sufficient wind shear to produce the wavy motion.

This wavelike motion akin to flapping one end of a blanket or bed sheet up and down can be seen most demonstrably in a timelapse of undulatus asperatus, such as what was captured by the National Weather Service in Columbia, South Carolina, on Monday morning.