Commercial airliners have a strange ability to create rain and snow when they fly through certain clouds. Scientists have known for some time that planes can make outlandish 'hole-punch' and 'canal' features in clouds. A new study has found that these odd formations are in fact evidence that planes are seeding clouds and changing local weather patterns as they fly through. In one case, researchers noted that a plane
triggered several inches of snowfall directly beneath its flight path.
This is a phenomenon I have witnessed empirically since the jet age took hold at O'Hare Field. Because of the exhaust gases (condensation trails) and pollution of unburned fuel, a microclimate has formed at O'Hare which is apparent to even a casual driver approaching on one of the expressways or tollroads which radiate through the region. On one side of the airport the weather will be sunny, then for about a 2 mile radius from the airport boundary the weather changes to gloomy and misty, then clear again once beyond the 2 mile limit. The total microclimate is an ever-changing shape (because of winds) ranging from 5 to 10 miles across at its largest diameter.
This microclimate effect (from other causes than plane pollution) is documented in places as disparate as Muir Woods in Marin County or Hawaiian rainforests.