Twin fallstreak holes in Kent

This unusual sight of twin fallstreak holes, or hole punch clouds, was snapped in Kent in the United Kingdom this week.

This unusual formation appears as a gap or hole in the surrounding cirrocumulus or altocumulus clouds. In this shot from Margate, they are altocumulus clouds.

Cirrocumulus are recognizable by their bright white color and tiny puff-ball appearance, whereas altocumulus clouds are darker in shade and larger.

These clouds are high enough and cold enough to contain supercooled water droplets. These water droplets within the cloud are sub-zero but not frozen.

Regular water, like our drinking water, contains small particles, allowing ice crystals to form at 0°C. Pure water droplets within clouds have no other particles present, remaining liquid down to -40°C.

When aircraft pass through the cloud layer, it causes the surrounding air to expand and cool. The change in temperature can then cause the water droplets to suddenly freeze into solid ice crystals.

These ice crystals then fall from the sky as virga, or fallstreaks, which is precipitation that doesn’t reach the ground.

It might sound surprising, but the process of freezing actually gives off a tiny bit of heat. This heat is enough to evaporate the surrounding water droplets, leaving the sharply defined hole in the clouds that you can see in the images.