Listener Question: Contrails
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Hi, I'm Dave Thurlow from the Mount Washington for The Weather Notebook and today we have a listener question about planes and weather: and this is Gordon Maclean from Atlantic Mine, Michigan.

"I listen to Weather Notebook on WNMU-FM in Marquette, Michigan. My question involves high flying jet contrails. Contrails sometimes disappear rapidly. Sometimes they hang around for hours it seems. Do contrails offer any sort of indication as what the weather might be in the near future?"

Well, yeah, they do. Here's how. When a plane flies overhead, occasionally you'll see a white trail behind it. That trail is called a "contrail", which is short for "condensation trail." And a contrail results is the condensation of water vapor onto the tiny pieces of smoke coming out from the jet engine.

Now as Gordon stated, sometimes a contrail sticks around for while and sometimes it goes away quickly. That has to do with how much moisture is there in the air already, as the plane flies through it. If the contrails disappear quickly, or there's no contrail at all, then the air is fairly dry. But if the contrail goes across the sky and stays there, there's a lot of moisture up in the air, way up at 30,000 feet where the planes fly. And if there's moisture up in the air, that means bad weather is on the way.

It's the first warning sign of a storm approaching from far to the West. So if contrails crisscross an otherwise blue sky, you can amaze your friends by making a forecast for rain or snow.

If you have a weather question, be sure to visit our website, which is weathernotebook.org, or give us a call at 1-888-RAIN-001; that's 1-888-RAIN-001. Thanks to Subaru, and to the National Science Foundation.