ScienceDaily (July 1, 2011) — Under certain conditions, private and commercial propeller planes and jet aircraft may induce odd-shaped holes or canals into clouds as they fly through them. These holes and canals have long fascinated the public and now new research shows they may affect precipitation in and around airports with frequent cloud cover in the wintertime.
http://www.sciencedaily.com/releases/2011/07/110701121623.htm