Airplanes taking off and landing at airports may be affecting the very weather around them. When a plane flies through a cloud containing supercooled water, which is liquid despite being below water’s freezing point, the plane triggers the water to turn to ice crystals and fall out as snow or rain. Such supercooled clouds might exist around U.S. airports some 5 to 6 percent of the time, scientists led by Andrew Heymsfield of the National Center for Atmospheric Research in Boulder, Colo., report in the July 1 Science. —Alexandra Witze
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