Have you ever looked up at the sky and spotted a curious gap in the clouds? These fascinating formations are known as fallstreak holes or "hole-punch" clouds.

Typically, these are circular or elliptical in shape. They form in middle-altitude clouds such as cirrocumulus or altocumulus. While these clouds are filled with supercooled water droplets that are below freezing, they don't become ice due to the lack of particles. But when particles do show up, they initiate the creation of ice crystals. This sets off a chain reaction where nearby droplets evaporate, leading to the large gaps we see.

What's more, these clouds can also form at lower altitudes, especially due to the movement of jets and airplanes. Andrew Heymsfield from the National Center for Atmospheric Research found an interesting cause.

As airplanes fly through these clouds, the sudden air expansion and cooling makes water droplets freeze and drop. This results in a widening fallstreak hole. While these occurrences are somewhat rare, keep an eye out for them near airports!