Is it possible to observe contrails as indicators of changing weather?
If a contrail is persistent or persistent spreading, then the upper atmosphere contains large amounts of moisture. If a contrail is short-lived, then the upper atmosphere is relatively dry. This was used by sailors and can be used today to somewhat predict the weather. Short-lived contrails may indicate fair weather, and persistent contrails may indicate an approaching change in the weather or precipitation. The weather signal is somewhat analogous to that of natural cirrus clouds. Q: There were two planes in the sky. One was flying north/south and left a persistent contrail. The other plane was flying east/west and did not leave a contrail. Why did one plane leave a contrail, but the other did not? A: The two planes were flying at different altitudes – air traffic control has rules for spacing flights in different directions – so that the north-south flight path contained more moisture or was at a lower temperature than the east-west flight-path. The amount of moisture in the atmosphe
