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Desert Diary
Climate/More on Contrails


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We've all seen contrails in the sky behind high-flying jets. We've also seen those airplanes without even a wisp left behind. With a little bit of background knowledge, we can have fun with contrails. They usually consist of clouds of ice crystals formed when moisture from airplane engines hits cold air, though at low elevations, they may be droplets of liquid water.

But why do they form trails from horizon to horizon sometimes and nary a bit at other times? That's where the fun part comes in. In very dry air, the moisture disappears into vapor almost instantly; in moist air, though, it lingers. In a general way, long contrails say there's moisture aloft, and a short trail that the air is dry. With a little bit of practice, you can be your own meteorologist. A bit of doubt? Start sky gazing. When conditions are right, you'll see a contrail appear only within patches of moisture-laden high clouds as a jet passes through. Contrails are just one more reason to keep an eye on our beautiful desert skies.
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Contributor: Arthur H. Harris, Laboratory for Environmental Biology, Centennial Museum, University of Texas at El Paso.

Desert Diary is a joint production of the Centennial Museum and KTEP National Public Radio at the University of Texas at El Paso.


The persistence of these contrails indicates plentiful moisture in the atmosphere. Photograph courtesy of the National Weather Service.