-- Jeff Nelson, flight instructor: A jet engine is very simple. It sucks in air, compresses and combusts the air, then blows it out the back as thrust. When the hot air exits the tailpipe the contrails occur because of the very cold air at flight altitude. Water vapor in the exhaust (produced by the combustion of the fuel) turns to ice crystals, and that's what you see as a white stream behind the plane. Those ice crystals quickly dissipate through sublimation and mixing with the surrounding air, and the trail disappears. "It never lasts more than a minute, usually [only] seconds. . . . What we're seeing now, and I first could not believe it . . . these are not normal, they're not natural. . . . It's got to be some outside influence doing that."

Ted Aranda
https://www.raftd.org/