What are the White Lines Left Behind by Airplanes?
Those white lines you see behind a plane flying high in the sky? They’re called contrails and no, they’re not smoke from the plane. They are “condensation trails” that occur when hot, humid exhaust from the engines mixes with the colder atmosphere at high altitude. This causes the water vapor in the exhaust to condense and freeze, forming a cloud much like the one your breath forms on a cold day.
The thickness, duration, and extent of the contrails depend on the aircraft’s altitude as well as the humidity and temperature of the air itself. A thin contrail usually indicates low-humidity at high altitudes whereas a thick, long-lasting one indicates high-humidity and the possibility of a storm.