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Hole Punch Clouds are simply high clouds that look like somebody punched a hole in them. The name is not scientific and sometimes you hear it as Punch Hole Clouds but they look unusual. If you look you could probably see them fairly often when we have Cirrus clouds but usually they are not too dramatic. On December 11, 2003 the sky was dramatic over Mobile County, Alabama. Washington County, Alabama later saw a similar event on January 29, 2007.
In the 2003 event, first a layer of Altocumulus clouds moved in from the west. Even though these clouds were made of water droplets they were actually supercooled water. In other words, the temperature of the water was below freezing. These clouds were just below airplane condensation trails (contrails) indicating that the humidity was high at that level of the atmosphere. Then close to noon, within minutes, the blanket of Altocumulus clouds developed a hole. The hole turned out to be crystals of ice, transformed into regular Cirrus clouds, and then falling. By definition this was precipitation and since Cirrus clouds are made of ice crystals, you could call it snow, fallstreaks, or Virga. It evaporated well before hitting the ground. All of this is common but what was uncommon was the perfect circular shaped that grew within a matter of minutes.
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Depending on where you were, it may have been hard to tell that the clouds in the middle of the hole were falling lower than the other clouds. For this phenomenon to occur you only need to do one thing- increase the relative humidity fast. There are several ways to do this.
An easy way to artificially raise the humidity is to fly a jet plane through the cloud. As the engines burn fuel, they release water vapor to increase the relative humidity. Ice crystals that are already in the air will pull as much of the vapor as possible and then grow larger, and heavier, to fall. This is one of the reasons we see condensation trails behind jets that fly high. Jet engines also release tiny particles that serve as a base for ice crystals to form on.
Other ways that relative humidity is raised naturally is when waves in the atmosphere cause the air to rise and sink, just like water waves near a beach. Rising air cools and that can cause the relative humidity to rise and produce precipitation. Even if the air sinks, it's possible that ice crystals may fall into a region of high moisture that is not frozen and immediately form big crystals.
Take a look at this high resolution satellite image of the central Gulf Coast. It shows natural clouds, condensation trails, and several areas where likely, a jet passed through the clouds and caused the clouds to precipitate in its wake. Here's a closer picture centered on southern Mississippi. Click on either picture for the original image.
The process is pretty simple but there are details. For example, It's possible to have water droplets when the temperature is way below freezing. We called them supercooled. It's also possible for the relative humidity to be over 100%
Pictures below are from NASA Terra satellite
on January 29, 2007
An even closer view in Texas south of the Red River. You can also see
ripples in the clouds. Some of the holes are up to 10 miles across.
In weather, there's an exception to every rule. See more cool pictures in our Photo Gallery.
