Lesson 1 of 4: The Role of Humidity
Humidity is the single most important factor determining how long a contrail lasts. It measures how much water vapor is already present in the air.
When the air at cruising altitude is humid, contrails persist and may even spread. When it's dry, contrails disappear quickly.
Ice crystals sublimate quickly
Contrail disappears in seconds
Like breath on a cold, dry day
Ice crystals absorb moisture
Contrail persists for hours
May spread into cirrus clouds