A picture of a cloud formation in Virginia that resembles rolling waves is going viral.
Weather experts say this type of cloud formation, which was spotted in over Smith Mountain Lake near Roanoke, is very rare.
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The formation occurs when different layers of the atmosphere have differing wind speeds.
The clouds are known as Kelvin-Helmholtz instability waves and are named after the scientists who studied the physics behind them.
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The formations are most common near mountain ranges and usually last only about 10 minutes.