About real clouds, weather, cloud seeding and science autobio life stories by WMO consolation prize-winning meteorologist, Art Rangno
A rare day, a rare “bird”; a day in which rain only due to the collision-with-coalescence process operateddeveloped; hold the ice
Yesterday was as rare a day in Catalina, Arizona as seeing the marbled murrelet in Olympia, Washington.1
Why?
Our bit of rain (0.12 inches in Sutherland Heights) was only due to that formed by the collision-coalesence process, some times called the “warm rain” process, or more technically, non-brightband rain2.
No ice needed.
Usually clouds at inland locations like Arizona have so many droplets in them , a few hundred thousand per liter or more, larger drops that can collide and coalesce don’t form because the condensed water is spread over so many of them.
So I could feel the excitement out there as that frontal band got closer. Perhaps you saw the drizzle-mist rainbow on the Tortalitas, looked at cloud tops, and saw no ice. If you said you saw some ice yesterday you were mistaken or lying to impress your friends.
Let us review yesterday in clouds:
7:36 AM. Looking toward the Tortolitas at the line of Cumulus congestus approaching Catalina. Can you see the little piece of rainbow just below those low,low cloud bases? Go straight above the white dot marker in the road (Oracle). Cloud bases were usually hot yesterday morning, 15-17° C, and, thus. our clouds were loaded with extra water. The warmer the base, the greater the amount of water that condenses above cloud base. That means drops is bigger, and can reach sizes where bumping together leads to sticking, not rebound as is normal. The usual cloud base is around 5-10° C this time of year. Photo, of course, not taken while driving; that would be crazy. Is just “shopped” to look that way to provide an “action” setting.7:40 AM. Such a pretty scene! Can you see the little bit of lower hanging cloud below the line of Cumulus? It looked like our windshift, cold front line might be on the doorstep. Waited until afternoon to get here, though.7:45 AM. Here’s a closer look at those lower windshift indicating clouds to the NW yesterday. Now you KNOW the front and “FROPA” is getting close. Very exciting scene. But would it rain? No ice was visible anywhere around.7:44 AM. In the meantime, Stratocumulus clouds gathered upwind of Catalina with light rain visible just above the horizon SW/ Was looking for an icy top. to extrude above the Stratocu, but didn’t see one. You didn’t either.7:49 AM. In the meantime, not much is going on over the Catalinas. Notice how much shallower the Stratocu are than just over there by the Tortollitas. Really showed that the lifting zone of the front was so close!8:22 AM. Suddenly, it was raining! If you don;t believe me there are drops on the camera lens in this photo. All this misty rain developed while the author, cloud maven person, wasn’t paying attention. Did that Stratocumulus develop rain, or did that bit of rain above the horizon move in? Maybe this can be answered at the next club meeting.8:25 AM. Starting to lose photo control here, as things closed in, prettyness getting enhanced be passing rays of sun on the greenish Catalina Mountains. How can you not record this? Well, maybe you can go ho-hum, but no cloudcentric person could.8:33 AM. By this time it was all over and 0.05 inches had been logged. Here, those raining clouds zip off to Oracle State Park and vicinity over the horizon. Still looking for icy tops, but haven’t seen any, such as in those Cumulus tops, horizon left. Photos now being taken almost every minute, certainly within every five minutes. Wondering if I need a doctor….?8:47 AM. Rain begins to form on Pusch Ridge from low-based Cumulus clouds. The misty look, lack of a shaft, has you thinking “warm rain” all the way, Maybe of Hawaii, too.
Skipping a LOT of pretty scenes now…..
9:47 AM. Think how special you would think you were when this ray of sunlight bathed you for those few seconds, darkness all around.9:48 AM. Pretty much the same scenes as you’ve already seen over and over again, but this one has a bird in it for the sake of variety.10:33 AM. A little break allowed some nice scenes of the Cumulus congestus on the Catalinas. Notice how low the base is. You could have been hiking in congestus bases yesterday! Very few people get to hike in the base of a Cumulus congestus clouds. You still haven’t seen any sign of ice, either.10:44 AM. Something in the way of a shaft out there over Marana/Oro Valley probably made you start to wonder, “maybe there is some ice up there?” It dissipated quickly before it arrived dropping only a few drops. Still has hard as you and I looked, we couldn’t see any as it came and its remains went. U of AZ computer model soundings at this time had the tops way above freezing. In case you don’t believe me again here is a sample:
Valid for 10 AM, yesterday. Output was from the 11 PM AST model run, a diagram with a lot of writing on it.
11:50 AM. Major windshift line and fontral passage (FROPA) now beginning to make progress toward Catalina along with a line of deeper clouds along it. Was thinking ice might be seen somehwere up there at this time, but nope.11:52 AM. When looking for ice, you want to look at what’s ejecting from the tops of the clouds. Here, that little flat cloud above the Cumulus clouds is the “ejecta” from those showers just starting to hit the Tortolita Mountains. As you can see as a cloud maven person, it does not have a fibrous look, nor are there fine strands of ice dropping from it, as would be the case if ice was present. SO it was another piece of circumstantial evidence that ice was not involved in even those dark clouds toward the Tortolitas, ones that would eventually give us our final bit of rain here in Sutherland Heights, Catalian. This kind of cloud has sometimes been called a “water anvil.” This was a really exciting moment, though most folks would find that hard to fathom.12 Noon. A hard shower has popped up over there toward Marana. Now here’s I would have guessed these must be some ice at cloud top from the narrowness of the shaft indicating a higher cloud top than in the other nearby shower-producing clouds. Does anyone out there have an aircraft and can fly IFR? It would be great to be on standby like days like this and go take a look at cloud top heights.12:38 PM. Stratocumulus, in one of its better presentations; lumpy and widespread.
The rest of the day was overcast, cool with a period of light rain around 2 PM, with the temperature dropping to a remarkable 58° F here in Catalina.
The last TUS sounding seemed to confirm this unusual rain day, indicating that the stratiform tops near and over the site were at 0° C.
Here’s pretty much what the balloon went up through: The TUS rawinsonde, launched around 3:30 PM yesterday. Cloud tops would be where the two lines, temperature and dewpoint temperature, separate.4:04 PM. Looking toward Pusch Ridge and Tucson.
Our final rain total in Sutherland Heights was a respectable 0.12 inches from a rarely observed event. 0.47 inches fell on Ms. Lemmon for the highest amount around.
Might add more later, but am quitting now to go “lunge” and ride a horse..
PS: I have added more, re-written some not so great “formulations”…
The End
1If upon reading that sentence you would like bail on reading about clouds and rain here in Arizona and read about that bird, please consult:
2When steady rain is occurring, returns have a bright band, or a augmented return from the layer in the atmosphere where snow is melting into rain. On days like yesterday, throughout the Tropics, along the West Coast, among many places, non-brightband rain is fairly common. Typically it falls from clouds with tops warmer than -5° C. Ice usually onsets at temperatures between -5° and -10° C in such clouds. Hawaii is a good example where “warm rain” produces most of the prodigious rain totals there on the windward slopes, such as that at Mt Waialeale on the Island of Kuwai where the average rainfall is more than 450 inches!
Author: 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.
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