So I've seen these planes with intense seemingly permanent contrails create a cloudy sky on a sunny day, then the next day it would be hazy.
Then I've watched other planes (on the same day) at varying altitudes leave little contrails, some of them last for a few seconds and some contrails...
...conspiracy nutter)? I can't ever remember seeing any contrails do they occur in Perth, or is the weather here not right for them to appear?
http://en.wikipedia.org/wiki/Contrail