Hole punch clouds in SoCal
© Jake Epstein
An unusual cloud formation drew the attention of many Southern California residents Saturday, with some taking to social media to share the rare sight from all over the area.

It was a so-called "hole punch" cloud, or fallstreak hole. These clouds are created by airplanes — specifically the propellers of airplanes, not engine combustion. Here is how they form: The first requirement is the clouds have to be vertically thin. Then a plane must fly through, which creates a big temperature difference. The temperatures beneath the wings of a C-130 airplane, for example, are 14 degrees warmer than the surrounding environment.

This temperature difference and propeller motion creates a dry punch of air falling from the sky, evaporating the clouds beneath. This is always the case, but if the clouds are too thick or the plane is above 20,000 feet, a hole will not occur.

Comment: Fallstreak holes are formed when the water droplets in clouds turn to ice crystals. The water around the crystals evaporate leaving a large circular hole in the cloud. These holes can be formed by passing aircraft, but there isn't much evidence that propellers caused these rare clouds to form over Southern California.

This is why hole punch clouds are fairly rare to see. But when you do get to see them, like Saturday, it's an incredible sight. Here are some of the photos sent to us from NBC4 viewers.

Hole punch clouds in SoCal
© NBC viewer

Hole punch cloud in SoCal
© Tony Belmont