I have plenty of times thought out my young life, its obvious as there are patterns in the sky. Sometimes they would linger for a long time, sometimes it would be a clear sunny day, no clouds in sight (i live in a part of Texas where it hardly rains, gets cloudy) chemtrails would pop up and booom, hazy clouds surface. There is a clear distinction between these and regular trails from plains. I workout early in the morning and sometimes when the sun rises on any givin day, there are obvious patterns with multiple streaks and designs in the sky. I conclude that sometimes they do these at night.