Photo Collection: Kelvin-Helmholtz Instability Clouds

As anyone who knows me will tell you I am passionate about the sky.  I love clouds, especially odd, rarely seen ones, and from an early age I have learned all I can about their names and what makes them form.  Today I will highlight my favorite "rare" cloud:  The Kelvin-Helmholtz Instability Cloud (or KH cloud, or wave cloud).  Its really only rare because if you aren't looking for it you probably won't see it.  It only lasts a few seconds to a minute (if you are lucky) and must be photographed "in the moment" or you will probably miss your chance.  As I have found its not so rare because I have quite a lot of pictures of them, and have also seen them when I haven't been able to take a picture.

First, what makes them form?

From what I have gathered from reading books and internet articles about them they form when wind shear moves past a cloud layer (liquid) going either faster than the speed of the cloud (liquid)or in the opposite direction.  A great example is wind blowing over water, creating waves (source).  This site also has a good explanation and a computer simulation so you can see how the instability works.

What do they mean for weather?

As the name suggests they indicate an instability in the atmosphere.  When you see these clouds it is very windy up there.  Airplane travel will be turbulent.  Generally when its really windy up there the weather will be changing.  I often see these clouds about 24 hours before a good storm rolls in when its summer.  Look around at the other types of clouds to see what's coming.  Most of our weather travels from West to East.

How did they get that funky name?

These clouds are name for Lord Kelvin and Hermann von Helmholtz.  Lord Kelvin, a Scotsman, was a physicist and a mathematician.  Hermann von Helmholtz was a German physicist, physician, and philosopher.  Both contributed to the discovery of the instability wave and therefore both are included in the nomenclature.

Here are my personal photos that I have taken over the past three years from Vermont.  Most in my hometown of Milton.  I hope you enjoy them!

June 24, 2010 Milton VT

June 28, 2010  Burlington VT

August 18, 2010 Milton VT

Bands of KH instability at sunset August 18, 2010 Milton VT

July 22, 2011 Milton VT

July 31, 2011

September 9, 2011  Williston VT

July 25, 2012 Fairfax VT

April 16, 2013 Westford VT

The next 3 picture are also from the same date, but later in the afternoon!

Just beginning to form...

This is what it became!

This was another one on the same day in a different part of the sky.

May 22, 2013 Milton

June 28, 2013 Burlington VT

June 28, 2013 Burlington VT

That is what I can find in my archives, of all my most dramatic and favorite ones!  Next post I will highlight Pileus caps on growing cumulus clouds :)  Any comments or questions are welcome!