Like giant breakers in the ocean surf, magnificent cloud waves in the sky crested and crashed above Virginia’s Smith Mountain Lake on Tuesday evening.
These rare clouds, known as Kelvin-Helmholtz instability waves, were spotted and photographed by Amy Christie Hunter around 8:30 p.m.
“It was the coolest cloud formation I think I’ve ever seen!” she wrote on her Facebook page. “It was so amazing.”
Hunter’s photo has gone viral, appearing on local and national television news broadcasts and websites.
Kelvin-Helmholtz instability clouds form from variation in air density between adjacent layers and the resulting difference in wind speeds known as shear. These clouds are extremely short-lived, and they break in the same fashion as a wave on a shore — as the bottom layer moves slower than the top layer, and the top billows over and crashes.
To initiate these wave clouds, you need a perturbation or disturbance to jostle the air flow. Usually, they last just 10 minutes or so before collapsing.
They’re most common near mountain ranges because of the stratified air above them, but they can form anywhere and show off the fluid nature of the atmosphere.
Here are two other textbook examples of these cloud formations, both from 2015:
From Breckenridge, Colo.
From the Galápagos Islands:
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