I received a half-dozen emails this week about some strange clouds visible on Wednesday.
A few asked (perhaps in jest) whether they were connected to UFOs or some paranormal phenomena.
Picture by James Robers
Picture by Kathleen Millen
They are not natural. Something artificial caused these strange cloud holes.
Aircraft.
These features have several names: hole-punch clouds, fallstreak holes, and punch hole clouds are some examples.
They are generally associated with a middle-level cloud deck, such as an altocumulus layer, in which the clouds are supercooled, which means liquid water clouds below freezing.
Typically, supercooled cloud water can occur when the air temperature is between 0C and -15C (32F to 5F).
Here is a satellite picture around the same time as the first picture was taken....you can see the extensive cloud layer.
It is fascinating that clouds can be made of liquid water that is below freezing.
However, things can change fast if such a cloud deck is disturbed by an aircraft that is either ascending or descending through it. Such aircraft passages can cause some of the supercooled liquid water to freeze. How?
One way is that the wings can cause pressure to fall, and that leads to cooling, cooling the air enough so that the water freezes.
Once one gets some ice, water vapor rapidly moves to the ice crystals causing them to grow and fall out.
This is a very fast process that quickly causes the liquid water droplets to evaporate and ice crystals to fall out.
A cloud hole is born!
You can often see the ice crystals falling out, and that is why they are called fallstreaks.
Don't like this explanation. Don't worry....there is another one.....
