Jan Bolinger (Member 65,050) was on the bike trail near her home in Plano, Texas, US when she spotted a cavum (the hole) and a distrail (the line) punched out of the Altocumulus clouds above. Both of these features formed in the wake of passing aircraft as they flew through the blanket of clouds.

This Altocumulus would have been composed of supercooled water droplets. These are droplets that have remained in liquid form despite being well below 0°C (32°F). It turns out that cloud droplets often remain in a supercooled liquid state like this, even at tens of degrees below water’s usual freezing temperature down at sea level. The vortices around an aircraft passing through the cloud can kickstart the freezing process, causing the droplets in the vicinity to freeze into ice crystals that grow large enough to fall below. Jan’s cavum and distrail features may have very different shapes, but they’re both just the gaps left behind as her cloud’s droplets froze and dissipated as they fell away into warmer, drier air below.