Tropical “soft serve” Cumulonimbus clouds sneak up on Catalina, deposit substantial morning rains

Maybe they sneaked up because I wasn’t looking.  After posting yesterday just after 5 AM, went out side and looked at the Catalina Mountains, that is those parts I could see through the thick rain shafts, and said, “WHAT!!!?”  I was STUNNED to see them; had not even looked at the radar imagery for a couple of hours.   Really was asleep at the keyboard.

And then the hour or so of rain that followed, with no lightning!  Rain is so rare here om the morning in the summer, and it was so substantial.    If there was a disappointment, a slight one, it was that Cargodera Canyon (NE corner of Cat State Park) with 0.87 inches, and the bridge at Golder Ranch Dr and Lago del Oro (0.71 inches) got  so much more than we did here in Sutherland Heights in the past 24 h (0.38 inches).  They were hit harder, too, by that late afternoon Cb that drifted off Pusch Ridge, again, a heavy shaft of rain with no lightning–how often have you seen that in a summer afternoon?

For a roundup of Pima County rainfall totals, go here.

It was, with its high concentrations of drops, a rain reminiscent of coastal Washington State in the early fall when offshore waters are still pretty warm, or Hawaii, for that matter, the latter location where most of the rain forms without ice.  Our high concentrations of rain drops was also likely due to forming, at least partly, through the “warm rain” process, one that does not require ice, and is VERY rare in Arizona.  Requires really warm cloud bases, and we had them yesterday, with bases around 60 F, 15-16 C, not too much cooler than you would find hovering over you in New Orleans or Miami, or Merida, Mexico, etc., places where warm rain develops routinely along with ice in the deeper clouds.

Here are some scenes from our huge, and low based, soft-looking, “soft serve” Cumulonimbus clouds, ones that looked that way because updrafts are weak for such deep clouds.  You will see that updraft weakness in these photos.

This will seem strange, but I thought yesterday, with its absence of thunder until around dark to the NE, was one of the most unusual days I have experienced here in the summer, so reminiscent of the clouds in the Marshall Islands near the Equator that we (the U of Washington’s research aircraft)  flew into during a ’99 field project down there; low, warm bases, high visibility under them, and clouds with weak updrafts and little lightning (the plane was only struck twice during the program):

11:44 AM. After the rain, this gentle giant.
11:44 AM. After the rain, this gentle giant.  No anvil, frosty glaciated slides that kind of slope upward, all indicative of relatively gentle updrafts, a situation that limits the amount of electrification that can build up in them.  I was in awe of how pretty this was, and how unusual its appearance was, too.  Had to stop, jump out in the mud and grab a shot.

 

11:46 AM. A closer look. I am just beside myself at how tropical this scene is, so I took another shot. Took too many photos, too.
11:46 AM. A closer look. I am just beside myself at how tropical this scene is, so I took another shot. Took too many photos yesterday, too.
2:31 PM. Another tropical looking scene on the Samaniego Ridge. Coulda been taken in the hills around Luzon, Phillipines. Note itty bitty rain shaft. Without doubt from drops colliding and sticking together, no ice needed in those clouds yesterday to do this.
2:31 PM. Another tropical-looking scene on the Samaniego Ridge. Cloud bases are running about 15-17 C here, 59-62 F.  Coulda been taken in the hills around Luzon, Phillipines. Note itty bitty rain shaft. Without doubt that from drops colliding and sticking together (“warm-rain process), no ice needed for those clouds to start raining yesterday.  I hope you enjoyed this unusual day as much as I did!  It was like being transported to a REALLY warm and humid climate, and yet, here we are in a desert!
3:06 PM. Maybe the "Dump of the Day". It was beginning to fade at this point, and as it approached Catalina, I listened intently for thunder, but none was heard. This, too, made it so "tropical oceanic" since those huge clouds with their weak updrafts, hardly ever have lightning. But I have never seen a shaft like this in the afternoon here sans thunder, making the day that bit more unusual.
3:06 PM. Maybe the “Dump of the Day”. It was beginning to fade at this point, and as it approached Catalina, I listened intently for thunder, but none was heard. This, too, made it so “tropical oceanic” since those huge clouds with their weak updrafts, hardly ever have lightning. But I have never seen a shaft like this in the afternoon here sans thunder, making the day that bit more unusual, and special.  I will never forget you, August 29th, 2013.
6:43 PM. Just the condensation of the water, and the accompany release of a little heat was enough even in the evening to send small clouds shooting upward, another sign of warm based clouds. The warmer the base, the more water is contained in the droplets that first form, and the more heat that is given off to the air next to the droplet. Those clouds were magnificent last evening on the Catalinas!
6:43 PM. Just the condensation of the water, and the accompany release of a little heat was enough even in the evening to send small clouds shooting upward, another sign of warm based clouds. The warmer the base, the more water is contained in the droplets that first form, and the more heat that is given off to the air next to the droplet. Those clouds were magnificent last evening on the Catalinas!  There was yet another Cumulonimbus beyond the mountains, too.
6:45 PM. Just two minutes later, I was thinking about that curry dish with mushrooms. I guess it shows how flexible the human mind is, going from this to that.
6:45 PM. Just two minutes later, I was thinking about that curry dish with mushrooms. I guess it shows how flexible the human mind is, going from this to that.

Well, that’s about all we have time for, kids, and the hour of the exede.com choke hold, 5 AM approaches, and its too frustrating to be on the Web after that. May dredge up a Kwajalein shot at some later point, for comparison purposes, though.

——Today——-

Dewpoints are still running very high, even several 70s in the state (68 F here in the Heights). And so, with luck and no drying and no appreciable changes evident, we’ll have another day in the Phillipines, or the Marshall Islands, or Puerto Vallarta, New Orleans, Miami, Panama, etc. Enjoy.

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.