This photo composite shows the development of a hole punch cloud and its attendant fall streak, during a time span of approximately twenty minutes, over Piberbach, Austria on August 17, 2008.  Photographer: Herbert Raab

Hole punch clouds can occur following cloud seeding, but they’re almost always caused by aircraft passing through a shallow, mid-level cloud deck. They’re not often seen but can be attention getting whenever they form. If the supercooled water droplets in the cloud layer are perturbed during a jet or propeller plane transit, the droplets will instantly freeze into myriad ice crystals. When this happens latent heat is released which warms the air and evaporates the undisturbed portion of the cloud. Ice crystals falling through the hole punch (the darkened patch near the center of the hole) are called fall streaks. These crystals almost always sublimate before reaching the surface.   [epod]

Hole punch cloud over USA:

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