NEW ORLEANS — The cool cloud seen across New Orleans yesterday is called a fallstreak or hole-punch cloud.
It forms in High to mid-level clouds that are made up of tiny water droplets that are much colder than freezing but have yet to freeze.
These supercooled water droplets need something to come along and help them freeze. Typically planes passing through the cloud layer can disturb the supercooled droplets by adding ice crystals.
Once ice crystals are added the droplets freeze and then start to fall and evaporate. A hole is left behind, which will start to expand outward as surrounding droplets start to freeze.