Mr. Cloud-maven person hasn’t said much about clouds lately, which is kind of ironic since he deems himself a “cloud maven” and not much more. Rather, he has been obsessing about POSSIBLE storms in AZ 15 days away which is kind of futile anyway.
So, as an excuse to show more cloud photos from that gorgeous day of snow and cloud shadows on the Catalinas yesterday, will go into a cloud lecture, a post-mortem so to speak. Here are some cloud shots from yesterday, most below the one at left. Note, not one cloud shows any virga yesterday, and some of them got, at least moderately humped up. A promiscuous cloud maven person might have called one or two of the cumulus clouds, a “Cumulus congestus” (though they would be WRONG). Well, maybe not that wrong–see the 1987 World Meteorological Organization International Cloud Atlas that I can’t stand because they goofed up on their cloud designations as you will see if you could only find one of those yourself. Still kind of bummed out by that atlas, but one member of that cloud selecting panel told me they were too busy in their Paris meeting going to the Eiffel Tower and such rather than paying attention to getting the cloud photos they had properly named. Now, where was I?
Right, I was talking about yesterday’s clouds…. Well, here are some cloud shots, ones that I was going to post 15 minutes ago before getting upset again over the 1987 WMO cloud atlas. (Really, I could have done a better job than the WMO all by myself; it was a real boondoggle, that meeting of “cloud experts”, yeah right.) OK, photos!
Now looking at ALL of these, you see no fibrous material falling out, even though some of the clouds look pretty dark in these perty scenes. I was so happy to be alive and live here yesterday, feeling very, very lucky. So, remembering the University that Bullwinkle Moose went to play football as the “Frostbite Flash”, “Whatsamatta U.”, we might say the same thing to these clouds, “Whatsamatta U?” How’s come there no precip falling out, and those who read this silly site will answer immediately, “Them clouds ain’t got no ice in’em”, which would be correct.
But why? It was awfully cold yesterday, and even Mr. Cloud-maven person, who does not even have the Master’s Degree, was wondering. So, off to the TUS “99 Luftballoons” sounding data for yesterday afternoon, posted by our great U of A Weather Department below (where the lines come together are where the clouds were located). Didn’t seem possible to me, but those cloud tops were hardly as cold as -5 C (23 F). Ice does not form in clouds, even though they are below freezing, at this temperature in the natural state except in very special circumstances. Ice formation in clouds, still not WELL understood, is known to be a function of drop sizes AND temperatures. Over the oceans where cloud drop sizes are large, it happens. Usually, someone can get a whole scientific paper out of a cloud that formed natural ice when the top has never been colder than -4 C!
Here in Arizona, what we would call a continental cloud forming environment. Cloud drops “is” smaller because there are so many more particles for the drops to condense on, and so the concentration of drops is higher, meaning the drops have to be smaller to condense out the same amount of water as over the oceans where the air has fewer particles for clouds to form on. In a nice cumulus off the Washington coast of the sizes we had here yesterday, the cloud drops would be as large as half the diameter of a human hair (“wow”, huge, he sez, 30-50 microns in diameter, for the sake of a number) here in AZ in those clouds yesterday would be lucky to have drops in them as big as 20-25 microns, too small to activate ice forming processes, known to be related to drop sizes. Oddly, the bigger the cloud drops, the HIGHER the temperature at which ice forms, especially if drizzle drops have formed. The drops in our clouds yesterday were too small to have an appreciable fall speed, so they don’t fall out either.
Since I have published a lot of critical work on cloud seeding, one might ask if these clouds could have been made to snow by artificial means? Even as a long time critic, the answer is an unambiguous “yes.” With a small plane, and a little dry ice, you could have made a little snow fall out of these clouds because the tops were cold enough for that. Dry ice, the substance you would have used, has a temperature of -78 C, and when pellets falling, they leave a jillion ice crystals in their path as they cool the air momentarily to -40 C and below, the spontaneous nucleation temperature. And, with ice in these clouds, the drops would be evaporating and the water molecules depositing themselves on the ice crystals. Ice crystals in clouds of water drops are like little low pressure centers; the water molecules leave the drops and goes to ice, and ice crystal gets big enough to fall out. Our natural precip here is like this most of the time.
So, summing up this little cloud-ice lesson, our clouds did not get cold enough, and at the temperature the tops DID get to, the drops weren’t big enough to trigger natural freezing. Tell your friends.