“A schlieren photograph showing the compression in front of an unswept wing at Mach 1.2”
The Prandtl-Glauert Singularity sometimes occurs when airplanes exceed the speed of sound.
“Prandtl-Glauert singularity effects can be readily observed on a humid day by successfully cracking a whip. A visible cloud is produced at the point where the tip of the whip goes transonic.”