Famed fine-arts photographer Clyde Butcher once said of Florida, “Out west they have their mountains. We have our clouds.” Butcher’s observation was spot-on, the Sunshine State is home to some incredible sights in our skies — be it the setting sun illuminating a far away thunderstorm, a wall cloud from an approaching tropical storm, or even just a regular day where the clouds take on shapes where they appear to be animals or something else familiar.

Every in once in a while, we see something incredible that looks other-worldly: “holes in the sky,” or cavum clouds — something that some folks have claimed were caused by extraterrestrial spaceships, or by “weather control” experiments by some anonymous and nefarious government agency. Apparently, alien life-forms have nothing better to do after travelling trillions of miles to Earth than make donut holes in the clouds.

No Super-Secret Government Agencies Needed

The truth is far simpler than that, cavum clouds are a natural phenomenon that is caused by “mid-level clouds are composed of liquid water droplets that are supercooled,” according to NASA’s Adam Voiland at the agency’s Earth Observatory website.

Supercooling is relatively common in our atmosphere — altocumulus clouds, for example, are supercooled and they cover at least eight percent of the Earth on the average. In simple terms, that’s when water droplets in the sky — the things clouds are made of — remain liquid even when they are below their normal freezing point.

Voiland goes on the explain further how that relates to cavum clouds, “Supercooled clouds have their limits. As air moves around the wings and past the propellers of airplanes, a process known as adiabatic expansion cools the water by an additional 20°C or more and can push liquid water droplets to the point of freezing without the help of airborne particles. Ice crystals beget more ice crystals as the liquid droplets continue to freeze. The ice crystals eventually grow heavy enough that they begin to fall out of the sky, leaving a void in the cloud layer.”

So, basically, a cavum cloud is usually created by a common airplane flying through a typical cloud structure and setting off a cascade of ice formation inside that creates this “hole in the sky.”

No aliens or super-secret government agencies needed, but a cool thing to see if a cavum cloud passes overhead.