Originally Posted by PHLDividends

"If a contrail is short and dissipates quickly that tells us the upper atmosphere is relatively dry and that good weather, i.e. high pressure, is likely to remain for at least another 12 to 24 hours. . . . However, if the upper atmosphere is nearly saturated, then an addition of a little moisture from a jet's exhaust will bring the upper atmosphere to its dew point (100-percent saturation) and a long and lasting contrail will form."

http://www.sailnet.com/collections/a...eid=carrmi0045