[John H K]

You seem to be victim of the FR sydrome, common on science threads, of people babbling about things they know nothing about.

Contrails routinely form persistent cirrus clouds under the right atmospheric conditions.

There are atmospheric conditions, of course, where you don't even get a contrail, much less a persistent one that spreads out into a cirrus cloud.

At times you'll have waves where an aircraft flying level will have a "dashed line" contrail" as it moves into and out of areas favorable for forming one.

However, in many situations aircraft form persistent cirrus in areas that would otherwise be cloud free.

[capt. norm]

To set the record straight, I am and have been a professional meteorologist for 34 years and operate the WeatherLab at Panama City (Florida) where we study such as that on a daily basis. It is you who have been fed a load of almost-fact.

Contrails form at a level where the dewpoint is below the freezing point of water. The dewpoint at upper levels of the atmosphere is cheked twice daily by weather balloons launched from NWS sites and is displayed on a plot known as a SKEW-T.

We study this day-in and day-out and you come along with something you have picked up somewhere that flies in the face of the actual facts.