RICHMOND, Va. -- Quite a few people noticed an unusual occurrence in the sky over Central Virginia Saturday.
These are not UFOs. It is a phenomenon called a fallstreak, or a "hole punch cloud." These holes in the clouds are typically caused by airplanes flying through the cloud deck.
Here is a technical definition from the National Weather Service:
High to mid level clouds, such as cirrocumulus and altocumulus, are often composed of tiny water droplets that are much colder than freezing, but have yet to freeze. [Usually, the water is the clouds is pure, and there is nothing for the water to cling to and freeze].
These "supercooled" water droplets need a "reason" to freeze, which usually comes in the form of ice crystals. Planes passing through the cloud layer can bring these ice crystals.
Once the ice crystals are introduced, the water droplet quickly freeze, grow and start to fall. A hole is left behind, which will start to expand outward as neighboring droplets start to freeze.
Sometimes ice crystals will fall from the cloud and evaporate in the air. In rare cases, the crystals do not evaporate, and this falls in the form of rain and snow.
For hole punch clouds to occur, conditions need to be ideal in terms of cloud height and temperature, so they are not seen very often.
