Kelvin-Helmholtz waves spotted above Virginia mountain .

A Virginia woman captured a stunning cloud formation above Smith Mountain, resembling a famous painting by Van Gogh.
Amy Hunter witnessed the Kelvin-Helmholtz waves, which usually form on windy days because of specific atmospheric conditions and resemble waves tumbling across the sky. The extremely rare phenomena occur when two different layers of air in the atmosphere are moving at different speeds - which is known as shear. When the upper layer of air is moving at a higher speed than the lower-level air, it may scoop the top of an existing cloud layer into these wave-like rolling shapes. One example is wind blowing over water, in which fast-moving air can create the waves on the slower-moving water. The occurrence is named after two meteorologists, Lord Kelvin and Hermann von Helmholtz, who studied the physics behind this cloud formation in the 1800s. The presence of Kelvin-Helmholtz waves could mean there is an atmospheric instability which often spells turbulence for aircraft. The rolling clouds have long been a point of fascination for those lucky enough to witness them and are believed to have inspired Van Gogh's 'Starry Night' painting. KDKA meteorologist Ray Petelin explained the formation to CBSLocal: 'Those are Kelvin-Helmholtz clouds. 'A very rare cloud pattern that is caused by velocity shear,' he said.' Velocity shear occurs when winds are travelling at different speeds at different heights in the atmosphere.''In the case of these cloud patterns, the winds are moving faster at the top of the cloud, than the winds at the bottom of the cloud, just like how waves are created on water. 'While these cloud patterns are very rare, the most often occurs when it is windy.'