Yesterday’s awful Cumulus clouds; better ones today!

From the University of WY Cowpokes, this awful sounding from yesterday afternoon at Tucson.  Where the two lines first pinch together, around the “500” label, is where the Cumulus cloud bases were yesterday afternoon (marked by the oval)!  To see why those Cumulus were awful ones with too much ice, check the temperature lines, the ones that slope upward to the right with the labels on the bottom, “0”, -10, -20, etc.   Yep, that’s right, the bottoms of those clouds were at 500 mb, and -20 C!  The Weather Cowboy sounding algorithm, the one that produces all the numbers in the column at right, thinks the bottoms of Cumulus clouds were even HIGHER, at 428 mb and nearly at -30 C (that “LCLP” number)!

So, the awful looking, dried out, Cumulus clouds have been explained.

Too high, too cold, too much ice.  Reminded me of the old days in Durango, Colorado, in the early 1970s.  Charming town, but awful place if you wanted to see Cumulus clouds without much ice.  Too high, too cold, and too much ice there, too.

What’s wrong with too much ice?

Too many ice crystals completing for itty bitty amounts of “condensate” (yes, Virginia, even at those temperatures, cloud begin as liquid droplets).  But when they are so cold to begin with, so many of the droplets freeze, that they all try to take the water from the ones that haven’t frozen (cause them to evaporate, the water molecules rushing to the nearest ice spec.

So when nearly ALL the droplets freeze, the ice crystals are all itty bitty as well, and can’t fall out, even though individually they may have a bit more mass in them than the droplets.  They just float up there and gradually die.

Stories from the field interlude

OK, gotta get this out…   In the domain of cloud seeding, where ice-forming nucleants are put into clouds, the phenomenon of having too many ice crystals would be called, “over-seeding”.  Believe it or not, deliberately “overseeding” clouds to make them look like the ones we had yesterday, and so that they wouldn’t rain has been tried!

Yikes.  Why?

The Coors Brewing Company, in the early 1970s,  did not want their hops in the San Luis Valley of southern Colorada (around Alamosa) spoiled by having rain fall on them at the wrong time.  The program was ended when alfalfa farmers in the same area, ones that WANTED RAIN, terminated the program prematurely with sticks of dynamite;  they blew up the seeding contractor’s radar, used to direct aircraft into the clouds to seed them.  Mr. Cloud-maven person, the writer,  was working in Durango in those days, on the other side of the mountains from Alamosa, on a scientific cloud seeding project (a randomized one) to see if seeding could cause more snow to fall from winter storms, so he was close to the “action.”

Yes, everyone gets excited about clouds and weather, especially alfalfa farmers!  Its so great.

Below a few shots of yesterday’s small, ice-ed out Cumulus.

The haze below this little Cumulus fractus cloud is due to ice having formed in it! Bad news from the get go if you're hoping for virga and rain later in the day.
Merely a Cumulus humilis, center, and having a bit of puffery. But its mostly ice. Quite awful-looking, really.

About today’s “better” clouds

Overnight there was an invasion of air from the east carrying increased lower level humidity. How cold will the bases be today after yesterday’s -20 C or so? Around 0 C our TUS morning sounding suggests. While that’s still cold, it should mean rain to the ground here and there in the fatter Cumulonimbus clouds that will be around even though they will be dominated by ice again. With these higher base temperatures, it means more water condensing in the clouds BEFORE ice forms. When that happens, you are likely today to get “graupel” forming in areas of the clouds where the condensation is greatest, and the ice just beginning to form. “Graupel” or soft hail, falls rapidly compared to ice crystals and aggregates of ice crystals (i.e., “snowflakes” to get away from jargon) and those graupel up there are likely to be what MAINLY gets to the ground today, melted of course, into raindrops. This because the “free air” freezing level is about 7,000 feet above us here in Catalina (3,000 feet elevation). Should be a fun day, reminding us of out upcoming summer rain season.

And, what do we think about when we think about graupel/soft hail forming in the clouds overhead?

Electricity, lightning!  Yes, these clouds will be getting “plugged in”, so to speak, this afternoon here and there.  Be watchful.


Nice display of Cirrus uncinus in the late morning as Cu began to form.

BTW, if you want a really expert discussion for today, go to Bob’s page here.  (He may weigh in on this later…) And,  of course,  our NWS here.  They seem to be getting pretty worked up and excited about today’s weather and all the wind that might blow out of our afternoon thunderstorms.

BTW, nice flowers out there in the desert now days; this on our “Arizona rose” (took about nine attempts to upload this!  Bad WP!)


The End.

By Art Rangno

Retiree from a group specializing in airborne measurements of clouds and aerosols at the University of Washington (Cloud and Aerosol Research Group). The projects in which I participated were in many countries; from the Arctic to Brazil, from the Marshall Islands to South Africa.