Last week Birmingham, Alabama was treated to an amazing display of clouds in the shape of waves, moving low on the horizon.
Although this is a spectacular event, apparently it’s not as rare as we might think. The formation is known as the Kelvin-Helmholtz instability. The phenomenon occurs when less-dense air (shearing winds) pull on denser air. It does of course happen in a similar way with fluid, when waves form in the ocean.
We can be thankful that on this occasion the event occurred in a heavily populated area, so some of the lucky people who witnessed it in person were able to video it for us to see via YouTube.