Have never seen anything like this, shot taken about 5:50 AM LST yesterday, July 26th. My best guess is that it was a partial rainbow, made possible by the small region of rain falling out of these Altocumulus opacus clouds. Probably some bulges in those tops above where the rain is falling so that they reached the “glaciation” level, but then the precip as snow, melts into rain just below cloud base. The low sun angle produces what would be the most gigantic rainbow ever, running about from due S to due N if complete. Is that even possible? The lower the sun angle, the dimmer the light, the larger is the arc of the rainbow. Will have to research this some more.
Some further thoughts… When you see VERY localized occurrences of precip from widespread cloud sheets like this, the possibility arises that it could have been created by the passage of an aircraft. An aircraft, under certain special conditions, CAN create precipitation in supercooled clouds–there was global publicity on this phenomenon recently asserting that airports could be affected by aircraft in snow situations. A friend was flying to New Hampshire yesterday out of TUS, and I wonder if her plane left this salutation? Hahahah, sort of. Most often, a hole in the layer is observed when that happens, and so the thought that it WAS an aircraft is somewhat suspect.
Go here, if you want to really get deep in this aircraft phenomenon. (Yes, Mr. Cloud-maven himself was involved in the reporting of this phenomenomanonanon)