https://www.washingtonpost.com/weather/2019/11/23/florida-cloud-becomes-fallstreak-hole-after-encounter-with-airplane-friday/

Natalie Keller Reinert looked up to an unusual sight Friday
morning in the Central Florida sky. The clouds above her appeared to have holes
in them.

What were the bizarre disappearing clouds? They’re known as “fallstreak holes,”
or more commonly “hole punch clouds.”

They typically form on stable days, when a blanket of altocumulus or
cirrocumulus clouds stretches miles overhead. These are generally fair-weather
clouds. But the secret to producing a fallstreak hole comes from what the clouds
are made out of — not ice, as would be expected, but water.

The clouds are high enough that temperatures are well below freezing. But
there’s nothing for the water droplets to freeze onto. So they remain
supercooled, suspended in the atmosphere with no place to go.

Until a plane flies through them, that is.

It’s believed that commercial aircraft — which eject water vapor, aerosols and
soot — can play a role in “seeding” the clouds. The newly introduced nuclei give
the supercooled a surface to freeze to.

The result? The cloud “disappears” into a trail of newly minted ice crystals.
Once in a while, a rainbow-like patch of color can appear in the diaphanous,
wispy tail.