Re: fires in california...

Have a read here:
http://contrailscience.com/broken-contrails/


--->"Same sky, same humidity, but different behaviors."

There's absolutely no way you could make that determination based on ground perspective. There are many different layers of humidity even within the same latitude. The atmosphere is a highly multivariate space. As such, you could have some planes making contrails and some making none to the onlooker, all on a so called "clear" day.

Remember, you are talking thousands of feet spacing that appear mere inches to the ground person's perspective. There is no way to measure or make judgments on RH unless you were up there in that space.

VOR