Fallstreak hole

A fallstreak hole (also known as a holepunch cloud) forms when part of the cloud layer forms ice crystals which are large enough to fall as a 'fallstreak'.

They form in clouds of supercooled water droplets, water below 0 °C but not yet frozen. These water droplets need a tiny particle, a nucleus, to freeze or to be cooled below -40 °C.

Aircraft punching through this cloud layer can cause air to expand and cool as it passes over the aircraft wings or propeller. This change in temperature can be enough to encourage the supercooled droplets to freeze and fall from the cloud layer in this distinctive pattern.

The images below have been sent in by  Met Office Twitter followers.

Fallstreak hole by Colin Hunter Fallstreak hole by Colin Hunter

Fallstreak hole by Katie di Stefano Fallstreak hole by Katie di Stefano

Fallstreak hole by Anne Muir Fallstreak hole by Anne Muir

Last updated: 5 August 2014