Δαφνη Ευτυχια Αρθουρος

What causes really short contrails? I just looked out the windows (police helicopter caught my attention so I went upstairs and OOH! REALLY COOL SUNSET!) and noticed four jets to the west, none of which had a contrail longer than a degree or two of arc. They look like apostrophes, except for the one close enough to see twin trails, which looks like quotation marks. I'm used to seeing contrails stretch at least a quarter of the way across the sky, and some days clear from horizon to horizon.

Is it simply a humidity/temperature thing?

(Interestingly, the tiny contrails are very brightly lit in gold by the setting sun. Gotta go load some colour film, since the camera I grabbed has BW in it.)

In other news, the police helicopter was hovering when I first got upstairs. It almost never hovers; it usually circles. It did move after several seconds though. (Someone explained to me why hovering consumes many times as much fuel as even slow forward motion in a helicopter, which I suppose is why the Baltimore police so seldom hover.