GOLDEN VALLEY, Minn. - Ask any one of KARE 11's meteorologists and they'll tell you that when it comes to viewer questions, no topic is addressed more than clouds.
A photo from the skies over Lake Vermillion in late August sent in by viewer Brett Arne is a case in point. The clouds captured along the horizon look like ocean waves and are called Kelvin-Helmholtz instability clouds.
These clouds are very rare and need very specific conditions to develop. In order to form, Kelvin-Helmholtz instability clouds need a very stable layer just above the surface 'and' a less stable layer directly above.
The best way to think of how these clouds are formed is to think of a wave in the ocean (which they look like). The atmosphere is related to the ocean more than most think, the only big difference between the two is that one is liquid water (ocean), and the other is water vapor (atmosphere).
Here's a quick explainer: An ocean wave forms as the current travels towards land. As the current brings water towards land, the depth of the water becomes gradually shallower until it reaches the beach. The water is forced to slow down as it gets shallower since the ocean floor can't move more water is flowing in than there is room for. The water near the ocean surface is less affected by the slow down and still moving at nearly full speed and at the same time, the flow at the bottom of the ocean reaches a standstill.
It's this scenario that causes the water to trip over itself and form a wave.
Now think of that same process except with water vapor instead of liquid water. This is what is happening when a Kelvin-Helmholtz instability cloud develops.
A stable layer of air near the surface is not moving, just like the water at the bottom of the ocean. But a higher layer of atmosphere is less stable and therefore is moving faster with a stronger wind than the layer below it, just like the water at the ocean's surface.
The cloud forms when one layer of air is moving over another, just like the current pushes the surface water over the stationary ocean floor. This is why the Kelvin-Helmholtz clouds look almost identical to an ocean wave.
A big thanks to KARE 11 Weather intern Klint Skelly for the explainer.
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