with a window seat you'll also notice..
...a vapor trail coming from the wingtips and off the edge of the wing. The physics of flight creates changes to the whole water saturation equation, especially with the pressure variable...a jet makes clouds. Linear clouds. If the atmospheric equalibrium is just so, these clouds can persist for some time, or do strange things.
You're right, Tech, it's fun to watch. My neck always gets sore when I've got a window seat.