Contrails and the Weather

Against a clear blue sky, a silver dot ahead of a contrail reveals a jet plane on its way between airports. Burning kerosene in compressed air provides the thrust to move the plane, its cargo, and passengers at over 500 miles per hour. Each pound of jet fuel combines with oxygen in the compressed air to produce carbon dioxide and water, about 1.2 pounds of water for each pound of burned fuel.
A short while after the water vapor leaves the engines, it condenses into visible droplets of water and ice, depending upon the air temperature way up there. A bit after that, the relatively dry air absorbs the water and the contrail disappears.
When the upper air is dry and cold, as it is when air descends under a high-pressure area, contrails will be shorter than when the plane flies though rising moist and warm air in a low-pressure area. The length of contrails thus can tell an observer something about likely weather conditions for the next 12 or so hours. Short contrails suggest good weather, and long and persistent contrails suggest an approaching warm front, or storm. While not infallible, contrails can reveal more than the presence of a jet plane hurrying between airports.