SACRAMENTO, CA - Sky watchers in Sacramento caught a glimpse of the rare hole punch cloud. It literally looked like someone punched a hole through the middle of the clouds.
The large circular gap forms in altocumulus or cirrocumulus clouds, which are high and mid-level clouds.
The clouds are filled with water that has cooled below the freezing point, called supercooled. For the hole punch cloud to appear, ice crystals need to form around the supercooled water. The water around these crystals will evaporate, leaving the hole.
Studies have shown airplanes can help create a favorable environment for the hole punch cloud to appear.
When the plane passes through the cloud deck, the lower pressure areas around the wings and propellers cause the air to expand and cool below the rest of the cloud. This starts the process for ice crystal formation. The heavier ice crystals can then fall to earth leaving the gap and circular appearance in the clouds.