http://www.lazygranch.com/images/flags/r2004_1/b2contrail.jpg
[Refering page http://www.lazygranch.com/red_flag_0401.htm]

Fortunately the chemtrail nuts haven't found this photo. Sometimes the
air is stable and the vapor hangs. Sometimes it doesn't.  Anyone who
has flown can feel the bumps in the air. Personally, I am amazed at how
parts of the air have different density since you would think air would
equalize quickly. However, I bet if I had formal training in the field
(meteorology), it would not be like black magic. It is like any other
science discipline. Get a degree in it, the magic goes away.