Here's something the ski industry and farmers might want to know more about: Planes can cause rain. Maybe you've seen it. A jet or turbo-prop airplane passes overhead, creating a hole-punch cloud, caused by supercooled droplets from other clouds freezing, in turn causing rain or snow to fall toward the earth below (but not necessarily reaching the ground), explains Discovery News. The effect is being studied by the National Center for Atmospheric Research in Boulder, and 9News takes a gander at a satellite image showing multiple holes---or tracks---in the sky made by planes, some 200 miles long and 10-20 miles wide, which last for several hours. "We might understand a little bit more about how we're interacting with our environment by understanding how these clouds are generated and how they affect their environment," says Andy Heymsfield, a senior scientist at NCAR. Here's what they know: If a propeller plane goes through a mid-level cloud, the thrust causes air behind the propellers to expand, cooling it. For jets, the air expands over the wings and is cooled (via Boulder's Daily Camera).