What Caused This Rare Cloud Formation in Western Iowa Yesterday?

It was, as my dad would say, "Windier than hell," yesterday in Iowa.

It was one of those winds that make your hands and head cold enough to where it hurts. It's one of those classic, 'Why did I choose to live in Iowa again?' winds.

Though there are plenty of negatives that come along with the drastic gusts and temperature drops, one cool thing did happen in the skies of western Iowa on Monday.

About 75 miles southeast of Sioux City resides the small town of Denison, population 7,988. For those who grew up in northwest Iowa, typically this city is known for being the closest place with a McDonalds, Pizza Ranch (sign can be seen below), and a multi-screen movie theatre. On Monday, it was home to another point of interest.

A natural phenomenon known as Kelvin-Helmholtz clouds appeared in the skyline of Denison, showing their rare, wave-like formation.

What caused them to show up in Iowa, though?

According to metoffice.gov.uk,

They occur when two different layers of air in our atmosphere are moving at different speeds (a phenomenon known as shear). When the upper layer of air is moving at a higher speed than the lower-level air, it may scoop the top of an existing cloud layer into these wave-like rolling shapes.

Kelvin Helmholtz instability is a scientific phenomenon not exclusively associated with clouds. It can occur wherever there is a velocity difference across the interface between two fluids. The most obvious example is wind blowing over water, in which fast-moving air can create the waves on the slower-moving water.

How did this unique formation get its name, you may ask? According to earthsky.org,

Kelvin-Helmholtz clouds are named for Lord Kelvin and Hermann von Helmholtz, who studied the physics of the instability that leads to this type of cloud formation.

Photos were captured by Danys Betts, Skywarn Storm Chaser CR438. Per weather.gov, "SKYWARN is a volunteer program with between 350,000 and 400,000 trained severe weather spotters. These volunteers help keep their local communities safe by providing timely and accurate reports of severe weather to the National Weather Service."