Very Rare "Kelvin-Helmholtz" Cloud Formation Seen In Vermont Thursday

Rare Kelvin-Helmholtz clouds over southern 
Vermont on Thursday. 

 Hat tip to the Vermont Skies page on Facebook for capturing some very rare Kelvin-Helmholtz clouds over southern parts of the state late Thursday.  

Kevin-Helmholtz clouds resemble a series of breaking waves. And they kind of are just that, actually. These are pretty rare.  The atmosphere needs the perfect alchemy of winds to make these clouds happen.  

As the Mount Washington Observatory explain:

"Lord Kelvin and Hermann Von Helmholtz, who studied physics that lead to this wave-like cloud formations, Kelvin-Helmholtz clouds form on windy days, when two different layers of air in the atmosphere move at different speeds. The winds in the upper layer of air move at higher speeds and cause cloud tops to roll over like a breaking wave. The atmosphere is split into layers when air densities change with height, for example, during temperature inversions."

It was not windy Thursday, but the Kelvin-Helmholtz clouds in the Vermont skies posting appeared to be high and thin.  At such high elevations, probably around 20,000 feet or even higher. It was surely windy up there.

The clouds appeared to form along the outer edge of cirrus clouds associated with what was then a developing nor'easter developing off the North Carolina coast. At the same time, strong, dry high pressure was sitting over Quebec. 

The Kelvin-Helmholtz clouds developed along the border between the two weather systems. 

Planes avoid Kelvin-Helmholtz clouds because there's tons of instability and turbulence around them. 

Kelvin-Helmholtz clouds are often hidden by other clouds, which is one reason why we don't see them that often. But everyone has a phone these days, Which means they have cameras. The Vermont Skies had lots of responses with photos, all taken in southern Vermont, and in nearby New Hampshire and Massachusetts.