Then this, looking straight up when CMP first noticed it because he wasn’t paying attention:
A few minutes later, as it moved away:
What happened? How cold were these Altocumulus clouds?
(Answers printed upside down below).
There were more, off in the distance, too.
Here are a few more shots of this phenomenon:
Now, we’re really quitting because I have other things to do, ones that have to be done, like discovering why our attic has so many rodents in it? Well, one, every so often, dammitall. Why is life one problem after another?
Answers not printed upside down instead:
It was an ice canal created in a highly supercooled layer of Altocumulus perlucidus. How cold? Whenever you see one of these in a middle cloud like Altocumulus, you can guess that its colder than -20° C. They’re rarely seen in warmer clouds. The TUS soundings suggested this layer was between -25° and -30° C. It mostly was ice free, bur regions of some slight (natural virga) were seen,
It was probably created by a jet, though the rarer prop aircraft can’t be ruled out. Seems to be associated with cooling around prop tips or some say over the wing cooling momentarily below around -40° C, though visually I would offer that its from the water-loaded exhaust, at least in jets, rather than air cooled as it goes over the wing.