Punch hole clouds are circular or oval openings in supercooled cloud layers that can persist for long periods of time as they drift with the clouds. These holes are thought to be caused by interactions between air traffic contrails and thermal inversions or pockets of cold air sinking through uniformly layered high-altitude clouds. Rare photographs show examples of these circular cloud holes from locations like Colorado, Alabama, Australia, and Tennessee that intrigued observers with their perfect shapes resembling celestial footprints or the work of UFOs.

1. Rarely Seen Cloud FormationsThere seems to be no end to strange cloud formations! From Punch hole clouds to cloud vortices, enjoy these rarely seen cloud formations!

2. Punch Hole Clouds may appear as a circular or oval holes in a layer of supercooled clouds; sometimes they assume a form of a perfect circle and persist for quite a long time, drifting together with the cloud layer. One explanation seems to blame the air traffic (the jet contrail intersections) combined with a thermal inversion (a circular motion of a rising warm air). Here is one, observed over the Gunnison Valley in Colorado:

3. Another strange hole in the cloud, reported from Mobile, Alabama USA, Dec. 2003 (and covered by BBC Photo taken in Melbourne, Australia in 2003

4. It seems both rising and sinking air currents can create the same effect. Sometimes a very stable, uniform layer of high-altitude clouds can get "punched though" by a pocket of cold air, which sinks toward the ground - creating the circular hole formationThese "cloud holes" can look like the footprints of some celestial being (UFO enthusiasts rejoice!) or can be amazingly round, like this pair observed in Gallatin, Tennessee by Wayne Carter

5. Cloud formations taken by NASA satellite

6. More Incredible and Fascinating Clouds