Fallstreak Hole Spotted in Rochester
The National Weather Service in La Crosse, Wisconsin has released some interesting information on a weather phenomenon it refers to as a fallstreak hole. It is also called a " hole punch cloud " and in meteorological terms, it is a " a large circular or elliptical gap that can appear in cirrocumulus or altocumulus clouds.
Here is more from the NWS on this event, which was noticed in southeast Minnesota yesterday, including Rochester.
How do they form?
High to mid level clouds, such as altocumulus, are often composed of tiny water droplets that are much colder than freezing, but have yet to 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.