I often see jet vapor trails as I sit eating grapes and
enjoying warmth of morning sun. At first the trail is very
narrow, but well behind the invisible plane, it sometimes becomes two parallel columns, and then one side only because broadened with tiny parallel barbs perpendicular to the one that stays a column, each gradually widening further
and fading, but looking like a mile long pinnate plume. I cannot imagine what the mechanism is that changes only one of the columns. Bean, where are you?

Here is a URL to a very large number of pictures of contrails. Some of them are of old prop driven planes at
lower altitudes.I couldn't find any that showed clearly what
I see here in Los Angeles area.
http://www.astro.ku.dk/~holger/IDA/S/choise.html

Apparently the conditions of air temp and humidity, and
difference in altitude make a lot of difference.