I’m glad you asked that question. Has to do with rules, cloud rules. It is true that at that altitude above the ground, 30,000 to 40,000 feet, we mostly think of cirrus or “cirriform” clouds. But those clouds, by our cloud definitions, cannot have shading during the daytime with ONE exception, Cirrus spissatus, a thick, but PATCHY ice cloud. Cirrus clouds CAN have shading when the sun is low in the sky, say, near sunset and sunrise. Widespread sheets of gray during the daytime, as we saw over Catalina two days ago, cannot, therefore, be called “Cirrus” unless you want to seem quite ill-informed about clouds. Below is an example of just plain Cirrus clouds, ones that floated overhead at about 100 mph (!) yesterday. In the first photo below, you would not be wrong, however, by referring to that thicker patch in the center as “Cirrus spissatus”, or more colloquially, “Cis spis.”
An example of “conversational meteorology” concerning Cirrus: you and your friend are horseback riding (as I do twice a week, really!) and you see this scene. The correct thing to say to your friend (in this case, “Nora”, who, interestingly, is not my wife) is; “Looks like we got us some Cis spis today. Maybe we’ll have one o’ them great sunsets again tonight.”
Well, that’s the way I would say it, anyway. And we DID have one of those GREAT sunsets last evening that make living here in Arizona so special. Below are a coupla shots of “Cis spis” at sunset yesterday. (There are some other varieties of Cirrus in these shots, but I won’t bore you with a list.) ((BTW, as an aside, a footnote, I’ve learned as a novice rider here in Catalina, that an awful lot of the guys don’t ride but their spouses do. One husband told me, “I don’t get on anything that doesn’t have a motor.”))
