While you are passing through a cloud with your seat back upright and your tray table in the locked position, your airplane could be triggering a freak snow shower. Last June microphysicist Andrew Heymsfield from the National Center for Atmospheric Research in Boulder, Colorado, showed that planes can punch holes in clouds, like the one at right, and change the weather below.
Ice crystals do not form easily, so water droplets can persist in the atmosphere even at temperatures far below freezing. Airplanes entering such supercooled clouds just after takeoff or before landing can cause disruptions that instantaneously freeze those droplets, Heymsfield says. When turboprop aircraft force air behind the propeller blades, or when jets cause moist air to flow over the wings to provide lift, the air expands and cools. Either one of those aircraft effects can drop the air temperature by more than 35 degrees Fahrenheit, flash-freezing the water vapor. That frozen vapor quickly forms ice crystals that drop out of the cloud as snow. Heymsfield thinks this might explain some of those winter travel delays. “The main effect will be locally induced precipitation,” he says. “Around airports, especially during wintertime, more snow is generated.”