A Royal Canadian Air Force CF-18 Hornet makes a near-supersonic speed flyby at the Cleveland National Air Show.
::geek speak follows::
As an object nears supersonic speeds, areas of low pressure form at various points around it due to the shedding of sound waves. If there's enough humidity in the air and/or the temperatures are right, clouds of vapor can be seen. These are known as Prandtl-Glauert singularities.
The speeds at which this CF-18 Hornet was traveling is in the range of what is known as transonic (between Mach 0.8 and 1.2).