On Sat, 2 Jun 2007 11:07:59 -0400, "Scubabix"
wrote:

http://www.airspacemag.com/issues/20...ight_Lines.php

This is a link to an Air & Space Magazine article on contrails. It points
out the 2 main factors needed for contrails are a temperature below -38 deg
F and humidity around 100%.

Rob

That was very good, thanks!