Residents of the Gippsland region in Australia were lucky enough to witness a meteorological phenomenon where a hole appears in a cloudy sky. As part of the cloud freezes, these particles fall but do not reach the ground, leaving a hole that is quite different to normal. This is commonly known as a virga.
http://www.nawcinc.com/photopages/SeedingEffects.htm
https://www2.ucar.edu/news/weather-modification-and-cloud-seeding-fact-sheet
http://corpau.blogspot.fr/2014/07/chemtrails-in-victoria-since-1967.html