AKA, Cumulus humilis virgae, or, with virga. While there were plenty of small Cumulus around yesterday, it wasn’t until after 1 PM that trace amounts of virga could be seen starting to emit from them as they got colder during the day. I think I did, too. By the end of the day, cloud BOTTOMS of those little clouds were about -20 C (-4 F)! Poor guys. Tops were likely only a little cooler, at -22 or -23 C. Those Stratocumulus bottoms topping the mountains in the third photo were about -5 C (23 F) already.
Here’s what happened yesterday. First, the tail of the frontal cloud band came by, dropped a few flakes on the Catalinas before rushing off. Here is that precip, barely detectable on the Tucson radar:
1. 7:43 AM. A haze caused by falling snow tops Samaniego Ridge. Ms.Lemmon is obscured.2. 8:43 AM. The dramatic looking backside of the frontal cloud band (looks like merged different layers of Stratocumulus) closes the book on precip. The lack of precip suggests cloud tops are warmer than -10 C.3. 9:06 AM. Final goodbye. Crenelated tops of castellanus, kind of cute, nice looking I thought. Stratocumulus clouds now top Samaniego Ridge, no precip evident, just cloud bases, but you knew that. I think its great I’ve taught you SO MUCH!4. 12:01 PM. Cumulus fractus amid the dust. Twin Peaks were obscured briefly in dust as the gusty winds developed later in the morning.5. 12:41 PM. Pancakes over the Catalinas, hold the ice.6. 1:16 PM. Then the ice! Can you find it? More educational than “Where’s Waldo”, though both are good for the brain. 15 points.7. 1:24 PM. Some more of that ice. This should be a little easier to find, but not really easy. Remember, ice means precip in these clouds! 15 points.8. 1:31 PM. Its still dusty, windy, I’ve been sitting out in it now for almost 2 h making this ice ID test up. This is the next level of detection. Can you find the ice amid a dusty sky? 10 points.9. 2:12 PM. Another tough one worth 10 points. The Catalinas are still so pretty with those cloud shadows traversing across them.10. 2:42 PM. A lot more ice, but farther away. This was part of a southward moving snow band that dissipated before reaching the Catalinas. 5 points.11. 4:45 PM. Where’s the ice? 1 point.
Extra credit:
What are the concentrations of ice particles in those clouds shown at 1:16 PM through 2:12 PM, photos Nos. 6-9? How about in the last two photos? 25 points.
Answer: Probably less than 5 per liter of those larger than, say, 150 microns in maximum dimension in 6-9, likely 10s per liter in photos Nos. 10-11.
Why know something as arcane as this?
Because it impresses the neighbors, for one thing, because then you can go on and on about the Wegner-Bergeron-Findeisen precipitation mechanism in “mixed phase” clouds, or simply impugn them, with the words from the Walt Disney Studios science song lyric in “Water Cycle Jump1“;
“Your brain is on vacation/if you don’t know about precipitation.”
Second, if you’re into “vigilante science”, as Mr. Cloud Maven person was in parts of his science career, knowing concentrations of ice in clouds by sight will help you clean up some of the messes in the domain of cloud seeding when people report concentrations of ice that are too low. But an extra low ice concentration report benefits them because it helps make the clouds seem like they need some of that seeding to make ice and then more precipitation. Then a big contract is let based on bogus cloud reports, ones that you damn well know are goofy just by looking at the clouds, or checking out rawinsonde cloud tops when its raining from them… I could go on, and on, and on….. Someday…will tell those stories.
I hope that helps explain why this is important. If not, oh well.
The weather way ahead.
Well, you all know about the hot ahead. Now some rain pixels have shown up on March 10th. Not worth showing, but will keep an eye on them.
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I am euphoric that this song is now online! I loved that song! Gritty but great, except the part where it is asserted that condensation leads to precipitation. Condensation (and the ice form of “deposition”) is only the first step. Also, if you like easy listening, boring music, don’t go to this site; it might be too much for you.
Condensation by itself can NEVER lead to precipitation. You got to have ice or those larger cloud droplets (again, let us call to mind, Hocking, 1959, Jonas and Hocking 1970 was it?) that cloud droplets do not stick together UNLESS they are around 38 um in diameter and larger, and then there have to be quite a lot of those that size and larger to “bump and stick” (sounds like volleyball) to form a true raindrop (mm sizes). You see, cloud droplets pretty much stop growing due to condensation at sizes TOO SMALL to fall out of a cloud as precip! They’d evaporate in the first 50 feet out the cloud bottom. NEVER forget that as a cloud maven junior!
I smiled seeing the groundskeepers scurrying about, sweeping and scraping snow off the courses and environs at the Dove Mountain golf tournament yesterday. I was smiling because the golf culture here is so different from that in Seattle, Washington, much more “pampering” here. Due to frequent inclement weather in Seattle, we have to toughen our skins against weather if we want to play golf. Rain? Snow? No problem.
In Seattle, golf season begins on March 1st. That’s because in March in Seattle, its only raining (or occasionally snowing) on every other day by then, not every day, as earlier in the winter.
So we’re going golfing on March 1st, dammitall, no matter what!
So shop keepers like this one below on Aurora Avenue in the north end of Seattle, knowing that Seattle golf culture, exult with big signs like this one when March 1st arrives!
The golf weather culture in Seattle, Washington, as represented by this sign. Photo by the writer, March 1st, 1990.
Inaccuracy in media re Catalina snowfall or maybe it wasn’t: a tirade
I was thinking that maybe a tirade would be a nice change of pace for you before some cloud discussions.
First, since I heard a weather presenter report that “2 inches” of snow fell in Catalina, a visual correction to that report. There was FOUR inches on the ground after settling/melting during the day and night of the 20-21st. If there is FOUR inches the following morning, it HAD to have snowed quite a bit MORE than FOUR inches! (The total depth of snow that fell was 5.5 inches here on Wilds Road).
Here is the proof, 4 inches of depth as measured by a raingauge dip stick, one tenth inch markers are 1 inch in length–I didn’t have a regular ruler. Some of the labels indicating light amounts of rain have worn off while the stick was being used in Seattle for 32 years, so you’ll have to count down from the 1.00, 90, 80 hundredths labels, ones clearly visible. For added proof I have added a second photo, and if you call now, you’ll get a third photo free plus for $75 for handling and shipping…
7:02 AM, February 21st. A raingauge measuring stick protrudes from a FOUR-inch depth of snow on a hitching post (where some snow could have even slipped off, or blew off!)7:04 AM. A slightly higher depth on a second hitching post–oh, yeah, leading the big western life here in Arizony with a horse and hitching posts.
I felt sad, though, remembering the words of humorist Dave Barry, speaking to the National Press Club back in ’91 I think it was, when he diverged from humor into a serious note, admonishing his Press Club Audience: “Why can’t we get it right?1”
Maybe in our case of the missing snow, it was because the person that called in the report was not a Cloud Maven Junior, and did not know how to measure snow. Maybe less actually fell where that person was (unlikely). Let us not forget that the snow on a flat board in Sutherland Heights, above Catalina proper, measured at nearly the same time as this, was SIX inches!
Yesterday’s clouds, and those snow-covered mountains
While it was sad to see so much snow disappear so fast, it was, overall, another gorgeous day in a long nearly continuous series of ones since the beginning of time here in Arizona, except maybe for those days of upheavals and dinosaurs and then when it was underwater, a remnant of the latter epoch as shown here in this fossil of a hydrosaurus, a precursor to grain eating critters like the Perissodactylas we have today…(horseys and such). As you can see, the teeth here were for eating something like mueslix, not for ripping flesh. I can’t believe all the information I am providing you today!
Possible hydrosaurus fossil encountered on a hike in Catalina State Park (still checking on what it is). Finding was reported to park rangers.
Here are some shots with some notes on them or in the captions. First those MOUNTAINS!
8:21 AM, February 20th, looking east from Sutherland Heights, which had SIX INCHES of snow on the ground at this time. Stratocumulus clouds top Samaniego Ridge.9:13 AM. The snowy Tortolita Mountains with some Altocumulus perlucidus above.
2:25 PM. With most of the snow already gone around Catalina, the majestic Catalina Mountains remind us of our great February 20th snowstorm and why we live here.
2:26 PM. While it was serene-looking over the Catalinas, to the southwest the sky was filling in with Cumulus and slightly higher Stratocumulus clouds. Why don’t you see virga even though we know they are at below freezing temperatures? In unison: “NO ICE!” (Tops too warm and cloud droplets likely on the small side.) This was to change in the next couple of hours.
3:24 PM. But first, another look at the Catalinas from Shroeder Ave in Catalina because I think its worth it before continuing. Golder Ranch Drive is on the far left.
5:25 PM. Clearly there has been a change in the temperatures at the tops of these clouds, likely now colder than -10 C. A trough of colder air was approaching aloft, and that likely lifted and cooled cloud tops. The cloud layer was due mostly to the spreading out of Cumulus tops (Stratocumulus cumulogenitus). The TUS sounding indicated cloud tops were about -13 C, capped by a very strong stable layer. There was a fall of sparse drops around this time, so some of it was getting to the ground.
The weather ahead
Cold then HOT. Hot when? Heat’s on already by March 1st for sure. Look at this “signal” in our trusty NOAA “ensembles of spaghetti” from last night:
Valid for 5 PM AST, March 1st. You won’t see a signal stronger than this one for 8 days from now. Likely will reach into the 80s when this ridge of warm air is fully developed.
The End, at last. Anyone still there?
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1Deadlines have a way of getting in the way of “truth.”
Three separate bands of snow in one day? Unforgettable, if not unbelievable, for Catalina, Arizona, made more so because its late February occurrence. Here at the top of Wilds Road we received a total of 5.5 inches from those three bands, with a peak amount of 4 inches on the “ground” (actually it was measured on a hitching post) just as the third and final band ended at 9 PM last night. The totals with each band, measured just about the time the snow was ending1:
Time of band Top of Wilds Road: Sutherland Heights (1 mi NE and 170 feet higher)
11:30 AM to 2:30 PM 2 inches 3 inches
4:30 to 6:00 PM 2.5 inches 2.7 inches (most fell in an hour and a half!)
8-9 PM 1 inch 2 inches (this just in), 6 inches on the ground there in sheltered locations)
Totals: 5.5 inches at the top of Wilds; 7.7 inches in Sutherland Heights. What a day, Mr. and Mrs. Catalina!
Water content in this snow here, 0.49 inches, so far. Waiting for melt down to get last few hundredths still frozen on the sides of the collector of the tipping bucket raingauge. Measured at Sutherland Heights: a fabulous 0.73 inches!
It’ll be gorgeous in the first few hours today after dawn, but with our late February sun, our great local scenes won’t last long. While more cold air is ahead, though with no precip in the few days, a HEAT WAVE has reared up in the models for the beginning of March, 8-10 days out!
Some photos for yesterday’s memorable snows2 (plural here is even amazing), From the beginning…
7:37 AM. A blustery, cool, and dramatic dawn scene, with snow showers in progress on the Catalinas from relatively shallow Stratocumulus clouds racing along them from the south.9:39 AM. A very exciting moment here! A non-preciping line of heavy Stratocumulus gets cold enough on top to start preciping over Oro Valley. Here we go! How cold were those tops getting? You want to guess, “Oh, about -10 C or so.” The TUS sounding at 5 AM AST had tops in that range already.11:37 AM. Just after the windshift and a 10 degree temperature drop from 44 F to 34 F, the snow begins to fall in Sutherland Heights.
6:11 PM. Wider angle view of that same scene after the second band dropped 2-3 more inches of snow in just over an hour. Getting pretty dark, camera or photog not doing the greatest job here.
5:59 PM. A blue palo verde tree bowing to snow.5:57 PM. “Piling it higher and deeper”, a common expression likely referring to snow and one that’s valid here.5:22 PM. How it got there… This is a shot during the heavier, second snow band during its prime S+ burst. “S+”, is “heavy snow” in weather teletype parlance, an early form of “texting.”
Will be taking more photos of course, early today!
The situation aloft (500 millibars) as S+ snow band 2 hit:
For 5 PM AST February 20th. The low center aloft is perfectly positioned for us as new precip bands are generated near its center as it sped eastward. Newer bands are heavier than older bands as a rule, and Band 2, was quite young with lightning in it. Band 3 is just forming, and it too, was mighty, though less extensive than Band 2.
Today’s clouds
Some Cu-Stratocu, patches of CIrrus and Altocumulus as a another lobe of cold air races SE from the Pac NW today. There’s a chance of snow flurries late tonight into tomorrow morning (can you imagine?) as the core of the trough goes by.
The End.
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1Measuring snowfall and snow on the ground, is one of the biggest bugaboos we have in meteorology. If there is any wind at all, forget about getting an accurate total, too much blows over the collector can. So, the precip amount reported for this storm is going to be on the low side. And, as the snow piled up yesterday, it was also disappearing at the same time on the bottom due to melting. Finally, as it piles up, it sinks down due to weight. So, the depths reported above are conservative, since if all the snow landed on a below freezing metal plate, we would only be dealing with one of those problems, settling, as with snowpacks in the high mountains.
2Hardly any of which was forecast from this keyboard. Wish there was a font smaller than ” 1 point” and this is it, in case you’ve never seen it. You don’t want to rub it people’s faces that maybe you were a little asleep at the wheel; too preoccuppied with the amount of precip which you forecast was going to be MORE than the models were predicting, and which happened, not the phase (solid or liquid) of the precip. But then, what REALLY matters to the vegies out there? The amount, of course, well, OK I guess vegies like it if more if the water sits there in a form that melts and has a lot of time to soak in.
That’s your weather forecast for today. There’s nothing you can do about it. Why go on about it?
Next, these from yesterday–was under control, only took 127 photos. Every thousand or so shots I take is NOT of a cloud, and yesterday there were two exceptions, which I will post here as an anomaly; a quirk really:
5:48 PM. Sun broke through the Cumulus and Stratocumulus clouds for this orangy foreground as the white light of the sun is burnished orange at low sun angles due to having passed through a denser portion of the atmosphere and the shorter wavelengths (blueish) are scattered out leaving reddish hues to come shining through. Banner cloud remains in the same crevice as yesterday on Samaniego Ridge like a trap door spider or a piece of lint in a corner of the room you haven’t vacuumed for awhile.2:55 PM. Horse demonstrating that the appearance of water in a tributary to the Sutherland Wash yesterday was real, not an illusion. Thanks, horse. The bit of water in the Sutherland Wash itself dried up just down from the private land fence opposite the rusty gate on the east side. (Horse people know where this is.)5:56 PM. Gritty view through wires and a telephone pole of the highlight color in Stratocumulus clouds of yesterday’s sunset. Sometimes I think you’re here only for the eye candy.
Yesterday’s rare ice-forming anomaly
I was hoping you wouldn’t read this far. Something incredible happened, rarely seen here in Arizona. Our slightly supercooled clouds, with top temperatures between -5 and -10 C, formed ice. When I first saw the indication of something falling out of those shallow clouds on the Catalinas, I was beside myself. Here’s what I saw, not taken while driving1:
11 AM. A shopped photo of the ice-fall from these Stratocumulus clouds on the Catalinas to make it look like it was taken from a car, the way you might have seen this ice fall. Note how I cleverly tilted the image to make it look like it was taken in a hurry before the light changed.Same image with writing and an arrow on it to help you out.
I thought it was some kind of fluke since it was indicated just yesterday from this keyboard, based on prior experience in Arizona, that ice rarely forms in our clouds at temperatures above -10 C (14 F). Maybe someone was nefariously cloud seeding I wondered…. Or had flown an ice-producing aircraft through these clouds upwind somewhere. (Its about what cloud seeding would do in marginally supercooled clouds like these, too, not much but something.)
———academic discussion—–
Ice appearance in clouds with tops warmer than -10 C is common in “clean” environments like over the oceans (see the works of Mossop in the Australian Pacific, Borovikov et al in the Atlantic, Hobbs and Rangno in the Washington State coastal waters and the Chukchi Sea offn Barrow, AK, or Rangno and Hobbs in the Marshall Islands) in clouds with warm bases (ones substantially above freezing for the most part) that can be anywhere even in “continental” environments far inland where cloud droplet concentrations are high due to natural and man-produced aerosols (see Koenig in Missouri, Hallett et al in Florida, Rangno in Israel) among many others). We sometimes have those warm-based clouds here in the summer, too.
——-end of academic interlude——–but not really——
These fuzzy very light snowshowers soon ended and the day went on as foretold, no ice in the clouds.While out on Old Jake, shown above, I was taking photos of particularly dark based clouds and was going to tell the story about why they looked so black, and yet did not precip–to warm and cloud top, and drop sizes near the top, too small for ice initiation. Just about every case in which aircraft measurements have been made in such clouds that form ice at top temperatures above -10 C (14 F), inside them are cloud droplets larger than 30 microns AND a few drizzle drops (liquid drops between 100 and 500 microns in diameter, or rain drops. Droplets larger than 30 microns and substantial concentrations lead to collisions where the drops that collide can coalesce into a single drop. Let us not forget Hocking or, later, Jonas and Hocking and the 38-40 micron drop size limits they found for this to happen from lab experiments. Below that 30-40 micron diameter size, the little cloud droplets act like marbles; too much surface tension.
OK, there’s that little discussion preparing you for what comes next. Continuing with the story…was there one? Well, anyway, Mr. Cloud Maven person, riding on his own forecast made that early morning for no ice in the clouds (meaning no rain), decides to also ride on his old horse, Jake, who needs some more of that exercise.
Confidently, though dark Cumulus clouds underlying a broken to overcast deck of Stratocumulus, looked even exceptionally dark in places, Mr. Cloud Maven person smiled at this darkness of the cloud bottoms, knowing that the darkness in the bases of shallow Cumulus only spoke to how high (and small) the cloud droplets were in those clouds; they had to be highly “continentalized”clouds, ones with tremendous droplet concentrations in them and because of that, all of the droplets in them have to be tiny, being so great in number. And, in being a Cumulus cloud with an appreciable updraft, even more droplets are activated in “continental” air than are at the bottom of a layer cloud like Altocumulus.
When the drops are tiny, more sunlight is reflected off the top of the cloud and the darker they get on the bottom, and the more removed they are from producing a drizzle drop, or are in having the precursor droplets to drizzle drop formation, cloud drops larger than 30 microns.
This is what a Cloud Maven person thinks before he gets on a horse….
So, as I am riding along near the Sutherland Wash, these patches of dark bases form nearly upwind…. I watch them for awhile, quite unconcerned, and smiled again, thinking about the other horseback riders, people on bikes out there that likely turned back in fear of a terrific downpour, not really having the knowledge they need about clouds.
Then suddenly I noticed ice streamers coming down NW of Catalina only a couple of miles away! It was falling from the downwind part of these darker clouds, where after a period of time, ice, if it was going to form would be. But, how could this happen?!!!! Before long, the thicker regions of the cloud began to emit stranded precip, a sure sign of graupel up top in the cloud. Graupel in clouds with supercooled droplets only 23-25 microns in size, much smaller than those required for coalescence, and the present of those droplets leads to ice splinters when they are banged by a graupel particle. A coupla graupel (soft hail) and after awhile, (10-30 minutes) a cloud can have a lot of ice, 10 per liter or more in concentration, plenty enough for precip beside the graupel-melting to rain stranded part. Here is a shot of the further, SHOCKING development:
3:06 PM. First graupel strands emit from base of Cumulus congestus. More ice aloft can be seen on the right. Horse, too, noting precipitation in the distance, is surprised by this sight. “It’s OK, Jake, its over there and moving away from us.”3:18 PM. I smiled, a sardonic one, as the drops began to fall (see smudge, lower center). A dark-looking complex of Cumulus topped by Stratocumulus had formed ice upwind of us (see upper right), and now, me and horse were going to get wet.
I had to laugh at myself on the way back, the rain drops wetting us down, when I thought about being quite confident yesterday morning about no ice would form in our clouds. When you have an occupation that tends toward error, its good to have a sense of humor. There’s nothing worse than a humorless meteorologist at a party, one whose likely obsessing over his error-filled life.
So, why ice? The TUS sounding at 5 PM AST did not suggest tops colder than -10 C Z(moisture top was about -5 C is all), but where the moisture ended, the air was incredibly dry, reported as “1 percent” relative humidity. Here is that 5 PM TUS sounding:
Arrows point to main top height, and where the highest Cumulus tops might have gotten to as they momentarily, due to inertia, mounded above the main moisture level. Normally, they plop back down because they get chilled, and the tops are cold relative to the surrounding air.
So, an overshooting top COULD have gotten to -10 C, and certainly, with that incredibly dry air just topside, those drops in those evaporating turrets would have chilled a couple of more degrees C. So, maybe that’s it, in fact, the overshooting moderate Cumulus tops DID reach to, or below, the -10 C normal ice-forming temperature here.
However, the concentrations that developed in these clouds HAD to be due to other processes beyond just the run of the mill ice nuclei since there are so few of them at -10 C, and that where drops larger than 23 microns come into play. Without those, there would never have been showers yesterday, only a very isolated drop or two. Those larger than 23 micron size drops lead to “ice multiplication” where just a couple of initial ice particles can “multiply” like rabbits in clouds because of ice splinters shed when hit by graupel. However, as we speak, the full understanding of how ice forms in clouds with these “high” temperatures has not been pinned down. Some researchers, the present one included, believe that ice splintering alone is not sufficient to explain the rapidity in the appearance the high concentrations (10s to 100s per liter) that develop in clouds like we had yesterday. You probably don’t care about what I think, but rather go with the majority opinion… Oh, well, it always safer that way.
As a test of even deeper knowledge that an aspiring cloud maven junior might have, this question:
What kind of ice crystals and other frozen particles would have been in those clouds yesterday?
No cheating; don’t get out your Magono and Lee (1966) translated-from-a-Hokkaido-University monograph on ice crystals and the temperatures and humidities that control their shape.
Answer1: What is a (hollow) sheath?
Answer2: What is a needle?
Answer3: What is a graupel (more a lump around a pristine ice crystal or frozen drop than just an ice crystal?
Answer4: What is an amorphous ice fragment?
Congratulations and adulation! You are now officially a cloud maven junior. Don’t forget to order that CMJ Tee.
Below, examples from the “ice crystal bible”, Magono and Lee 1966:
Needles, followed by sheaths, followed by “lump” graupel, and then some ice fragments in the last two panels.
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Only a crazy person would take photos while driving, like that crazy woman I once knew whose hobby was taking photos of dust devils while driving! Oh, my.
On a movie-sounding title theme again today, or this title could be the title of a bedtime story for kids, one that alludes to the Greek citizen bee keeper, Perlucidus, due to his early work in distributing hives, honey and honeycombs. Some cloud patterns resemble honeycombs, and so when Luke Howard decided to create a Latin system of names for clouds around 1802-03, he wanted to pay homage to Perlucidus1. Yesterday morning we had Altocumulus perlucidus and those clouds are discussed in detail below the lengthy “historic learning module” below.
——historic learning module————
Our Latin cloud naming system follows the tradition of Latin names first established in the hard sciences like botany and biology. After they did their naming thing, we weather folk decided, under leadership of Luke Howard, to “join the club”, to sound like the other scientists of the day when we were talkin’ clouds, that is, pretend to be on as solid a foundation as, say botanists, whom we likely envied, by creating a similar Latin naming system for clouds. That would show them!
Unfortunately, we really didn’t know what clouds had in them in those days, there were no aircraft measurements. Were they ice clouds or liquid droplet clouds, a mixture of both? And so the naming system that was developed came out a little fuzzy; flawed really. I guess “fuzzy” is appropriate for clouds. As the singer said, “I really don’t know clouds at all2.”
OK, after that “side lobe”…an example of fuzziness and flaws in our names: while Stratus and Altostratus have virtually the same name, and can look VERY similar on occasion, one (Stratus) is completely composed of droplets, and the other (Altostratus) is almost always completely composed of ice particles and snowflakes (aggregates of ice crystals, bunches locked together). No doubt Howard saw the visual resemblance from the ground, and may have thought they were composed of the same stuff.
Yet, from the name of Altostratus, you would think it is a droplet cloud like Stratus, but just located at a higher level (“alto” meaning “high” in Latin). Even our scientists confuse Altostratus in their peer-reviewed papers with something else because of this naming problem. A better name, since Altostratus is full of ice precipitation (unknown when Howard was making up his names, of course) would have been, “Altonimbostratus”. Nimbostratus, by definition, is a precipitating layer cloud, too.
Another problem in our naming system is that unlike in botany, where a redwood tree does not become a pine tree over time, clouds are always morphing into new forms.
And then we have to come up with silly expressions such as “Altostratus opacus cumulonimbomutatus”, what might pass for the remains of a Cumulonimbus cloud that has lost its base and only the heavy, higher level ice-cloud anvil (Altostratus) remains.
So, as Howard was attempting to follow the Latin scientific naming conventions of the day for clouds, up popped the descriptor, “perlucidus” for clouds patterned like a honeycomb in homage to Perlucidus1.
Two cloud genera (there are TEN3-I really like footnotes. They give a piece a really erudite feel even when its not), have the descriptor, perlucidus attached to them because they can attain a honeycomb pattern. These are Stratocumulus and Altocumulus, to repeat.
——-End of historic learning module———–
Yesterday we had some very cold Altocumulus perlucidus, some cloud elements shedding ice and disappearing because of it. The TUS morning sounding indicated these were in the range of -25 to -27 C. Here’s what these clouds looked like when they were still mainly composed of liquid droplets:
7:29 AM. Classic Altocumulus perlucidus (honey-combed pattern) with fine veils of ice crystals falling from many of the droplet cloud elements.
9:15 AM. Here, in brighter light, one can see the droplet clouds at left, while there are patchy, hazy regions in between. Those are the ice crystal remains, “ghosts” of the perlucidus cloud elements that have completely changed into ice (glaciated).
9:24 AM. Ovalized shot of the icy ghosts of perlucidus. There really is no cloud name for this grouping.
Strange Brew yesterday
There were also some very strange looking lower clouds as dry convection, associated with that little warming we had yesterday afternoon during this historic cold wave, bulged upward into a pretty moist laminar stable layer that resisted like heck being pushed up. When it was pushed up by that convection, which with greater moistness you would have seen as small Cumulus, instead you got slivers of clouds on top of where the Cumulus should have been. Those slivers of moist air that just reached the condensation level where droplets form in the air sliding over the top of the “invisible Cumulus.” The result, these odd forms shown below, resembling lenticular clouds with ragged bottoms in some cases:
12:15 PM. This dome shaped oddity. Was only there for a minute or two. Jumped out of car to get it. I hope your happy.12:38 PM. Then over the Catalinas, these strange forms of lenticularis clouds likely forced by dry convection rising up from underneath.
The last photo of a band of Stratocumulus with a ton of ice in it is worthy of a comment. A few days ago, the models had this day having significant precip, precip that would have been snow, followed by the same vast clearing we had later yesterday. Imagine last night and this morning’s cooling air augmented by a snow cover! Yikes. Woulda been 5 degree colder than what is already a pipe bustin’ cold morning. Wouldn’t have had so much afternoon melting because the ground has been chilled for several days now.
Wishing you happy pipes this morning. They’re freezing up here, temperature now 22.x here.
BTW, the list of Arizona low record temperatures will grow substantially today, as if you didn’t know it.
The weather ahead? Warmer. Can it be otherwise?
Also at 12:38 PM, looking farther down the Catalinas. Strange indeed.1:23 PM. The end of the clouds was at hand when this band heavily glactiating and higher-than-normal-based Stratocumulus clouds came over. (The elements were too large to be Altocumulus.) Some flurries could be seen falling from these clouds on Mt. Lemmon at little later.
The End
——-
1Shockingly, this part has been completely made up.
2She also said, “Ice cream castles in the air”, followed by, “Feathery canyons everywhere.” And finally, “Clouds got in my way.” (BTW, “Clouds got in my way”, too, as if you couldn’t tell!)
3The the ten are: Cumulus, Stratocumulus, Nimbostratus, Altostratus, Altocumulus, Stratus, Cirrus, Cirrostratus, Cirrocumulus, and the mighty most of the time, Cumulonimbus.
First of all, Happy New Year to both readers! Thanks for hanging in there.
The weather ahead…
before a long diatribe about drizzle, followed by some pretty pictures with explanations:
Some picaresque Cirrus later today. Looks like next chance for rain is around the 10th-11th of Jan.
A rare drizzle occurrence
Cloud maven juniors were probably excited beyond description when they went out yesterday morning between 9 and 11 AM and intercepted a rare occurrences of brief drizzle here in Arizona falling from that low-hanging Stratocumulus overcast. This happened after several very light RAIN (not drizzle) showers dropped another 0.02 inches, raising our storm total here in Catalina to a respectable 0.30 inches.
Drizzle is composed of drops barely large enough to cause a disturbance in a puddle of water1, as though a large particle of dust had landed in it. Drizzle drops nearly float in the air (should not be falling at more than about 3-4 feet a second), and in many cases of very light drizzle, the drops can float around like “desert broom” seeds. Visibility is usually lowered, things look fuzzy in the distance. Drizzle precip is so light it can’t produce even 0.01 inches except over periods of an hour or more. Drizzle drops are also more uniform in size than the drops in rain, and are usually very close together.
While drizzle is common along the west coasts of continents in coastal Stratus and Stratocumulus clouds, its much rarer at inland locations such as here in Arizona, thus, the excitement over seeing it yesterday.
The reason why its rare in AZ?
Shallow clouds that drizzle must be what we would term, “clean” clouds; they don’t contain many cloud condensation nuclei and so droplet concentrations are low, maybe 50-200 per cubic centimeter (might not sound low, but for a cloud, it is). Clean evironments are found over the oceans and for awhile, in air coming inland along the west coasts of continents in onshore flow before it gets contaminated with natural and anthropogenic aerosols (smog). Man, we are getting into a real learning module here! Wonder if any readers are left? Probably talkin’ to myself now. Oh, well, plodding on. Nice photos below…far below.
Drizzle occurrences tell you a lot about the clouds overhead. Not only are they low-based as is obvious (they have to be or the drizzle can’t reach the ground), but they are relatively shallow clouds no matter how dark they look. Furthermore, and more subtle, they have larger cloud droplets (ones to small to fall out as precip) in them that must be larger than about 30 microns in diameter (smaller than half a typical human hair diameter). When this larger size is reached in clouds, and those drops are pretty numerous, say 1000 per liter, they begin sticking together when they collide in the normal turbulence in clouds. Those collisions with coalescence result in drops that fall much faster, bump into more drops, growing larger and larger until they fall out the bottom.
In a shallow cloud, those drops can’t get larger than drizzle drops, and that’s one of the ways you KNOW that they are shallow no matter how friggin’ dark they look.
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Aside about rain not due to the ice process:
The largest drop ever measured, 1 cm in diameter, was observed in a Hawaiian Cumulus cloud that did not reach up to the freezing level! Unfortunately, the authors of this finding did not publish their results and so did not get a Guinness record like me and Pete Hobbs did when we reported a smaller 0.86 centimeter diameter drop in Geo. Res. Lett., 2004–found them in Brazil, and again in the Marshall Islands–hit the pilot’s window like little water balloons. Instead of being in a book with other famous people, like ones who can eat 47 hot dogs in 12 minutes, those researchers who encountered that larger drop in Hawaii sat on their finding! Unbelievable.
Strangely believe it, from lab experiments, drops bigger than 0.5 cm are not supposed to exist, but rather break up around 0.5 centimeters in diameter. (hahahahaha, lab people). End of aside.
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1Officially, 200-500 microns in diameter, equivalent to a couple or three of human hairs, maybe ONE or two horse’s tail hairs, to add a western flavor to the description.)
Yesterday’s gorgeous skies!:
Took more than 100 photos yesterday. Was out of control, euphoric, thinking how great this earth is, maybe leaning toward thoughts of higher being and creativity therein, thus explaining the “creative” punctuation above. Here are a few shots of those magnificent clouds and our magnificent, snow-covered Catalina Mountains. First, those drizzle-producing clouds:
10:12 AM. Last of the drizzling Stratocumulus overcast. Patchy area of drizzle to west on the Tortolita Mountains here. The Stratocu gradually broke up after this time.
11:54 AM. Stratocumulus clouds still in charge, but lift here for a peak at the new snow on the Catalinas.12:13 PM. First snow showers appear to the north-northwest as the stratocu deck begins evolving into Cumulus congestus and small Cumulonimbus clouds with large breaks.12:35 PM. Snow showers from relatively shallow Cumulus race along the Catalina Mountains. These kinds of snow showers occurred right up until late afternoon.12:37 PM. Snow and light rainshowers from shallow Cumulonimbus clouds also begin moving into Oro Valley before striking the Catalinas. Look at how similar these smaller clouds with their rain/snow shafts appear to our summer giants.12:59 PM. Shower over the Oro Valley moves onto the Catalinas. Arrow points to a filament/strand coming out that is almost certainly composed of graupel (soft hail), something that was common yesterday from these clouds.2:38 PM. HOWEVER, graupel often falls out of Cumulus congestus clouds on their way to being a Cumulonimbus without any sign of precip overhead, as here. This is because you are getting the result of the very first ice to form and fallout, usually those first ice particles are pretty rare in many of the shallow clouds as we had yesterday, and, because the updrafts are weak, they fall out as isolated little snowballs, too few to produce evidence of a shaft. But hang on, a shaft often, in the deeper clouds, imminent.Also at 2:38 PM, looking northwest. A view of smaller Cumulus with the deep blue of the winter sky we love.3:07 PM. “Congestus on the Catalinas.” You might ask, “where’s the ice?”, since yesterday all clouds reaching this size produced ice/snow/rain. Well, its on the other side (due to wind shear that carried the ice off toward the east. I think that’s the real reason why “the bear went over the mountain”, as we used to sing.
3:11 PM. Example of the medium Cumulus clouds (mediocris) that developed ice in them yesterday because it was so cold aloft, tops here colder than -12 C. (estimated). Arrows point to ice, necessary for measurable precip here.3:50 PM. Another modest Cumulus with plenty of ice (probably 10s per liter if you were guessing). Lowest top temperature likely lower than -15 C.
4:08 PM. I have no idea. This patch of ice cloud is left over, a “ghost” really, of a medium Cumulus cloud whose droplets evaporated. But what would it be called now? Altostratus translucidus cumulomediocristransmutatus? Cirrus spissatus cumulomediocristransmutatus? Silly, but I know of no name for such a patch of ice/virga4:49 PM. You knew that on this cold day you would be treated to some of our finest scenes in winter, golden scenes of cloud-capped, snowy mountains, and later, those rosy under lit remaining small Cumulus and patches of Stratocumulus. What a fine day it was!
The models are showing a lot of rain ahead over the next two weeks–see farther down. In the meantime, this:
6:44 AM: back side of last rain blob passing over Catalina now. That should be it for today and the next several days.
It was STILL raining when I got up at 3:40 AM, another few minutes of rain in a never-ending series of brief light rains over the past 24 h. The total now over the past 72 h is no less than 1.34 inches here in Catalina! Wow.
And yesterday, with its persistent overcast, dark, dull, spritzed-with-mist periods of rain (approaching the official “drizzle” precipitation category), was, with its high temperature of only 53 F, as close to am early spring day in Seattle in Catalina as you could experience.
Here are some shots of that overcast with Stratocumulus day with exceptionally long captions as well, a style I seem to have “pioneered”:
10:20 AM. “Catalina Heights” in the foreground, and the Catalina Mountains topped with snow and orographic Stratocumulus as seen from Shroeder Street, a street BADLY in need of re-paving but our priorities are so SKEWED, we think building three sound walls along Oracle in the near future is more important in this time of austerity! Sorry, got worked up here over our 3rd World streets in Catalina, in which it is deemed a “fix” of a pothole by dumping a loose clump of asphalt in it. Still upset, too, over the blockage of the CDO wash by sound wall on Oracle. Outrageous since there are no homes behind that section of the wall and beyond.1:14 PM. Another area of light rain invades Oro Valley from the Tortolita Mountains to the west. This rain, having no strong shafting, tells you that the tops were humping up like rolling hills rather than are like towers. In humping up, they have gotten cold enough to have ice form in them whereas the other areas of Stratocumulus with no precip tells you they are too warm at top to form ice. SO Seattle-like here! TUS sounding yesterday afternoon indicated main tops at -10C (marginal for ice here) but likely humped tops to -12 C to -15 C, where ice can readily form.)5:06 PM. Slight color under mainly non-preciping Stratocumulus. Oddity here is that orange, sunlit haze on the left of Twin Peaks. Seemed to be moving right to left almost like a dust episode.
And this last rain episode, not even lasting 10 min, has plumped up the rain total for the past 24 h to 0.39 inches here in Catalina at 6:45 AM, ABOVE that amount that it was deemed there was only a ten percent chance of exceeding, 0.25 inches when writing yesterday. So even as much of a precipophile as I am, I could NEVER have foreseen so much here as in the past 24 h!
So, this morning, I am humbled, but feeling great that so much more rain fell in our droughty nearby desert.
Two sites in the Catalinas have received another 0.87 inches as of 5 AM AST, 0.75 inches in the past 6 h! View 24 h totals here, though being a rolling archive, unless you go right away you’ll see slightly different totals than I mention here.
This last 24 h of our rainy spell, too, is a good example of how Catalinans get more rain than in town WHEN the flow turns from almost due south as it was on Friday, to more from the southwest and west as has been the case yesterday and continuing into this morning. When the flow is more westerly, air piles up against the Catalinas AND over us deepening the clouds, ones that begin thickening well upwind, say around I-10 to the west, and then they often start preciping soon after they thicken up as the tops of the clouds get colder and reach the ice-forming level. When the flow is from due south, we are “shadowed” by Pusch Ridge and other portions of the Catalinas to the S, and our rain can be less than Tucson and the north metro area next to the Cat Mountains.
Most of our rain advantage over Tucson (17 inches vs. 12 inches) comes from the kind of days we had yesterday and early today.
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What can we learn from these past 72 hours?
When you’re in a “trough bowl”, as we are now , good things happen; storms often turn out to be better than you imagine, being all they can be, no duds.
“Nice” days now will only be temporary breaks while we’re in the trough bowl, the collecting zone for storms. As an exciting example of how the weather is in a trough bowl, there were TEN model output panels from last night’s run showing rain for SE AZ! It can hardly be better than that! Here are a couple of early panels with rain:
The 6 h ending at 11 AM today (unbelievable to me that its STILL raining in the mod then! Its like the “Miracle in Albuquerque” yesterday when the AZCats beat Neveda but had to score two TDs in the last 90 seconds to do it, doesn’t seem possible, will turn off TEEVEE and go do something else (as a friend really did. But there it is, its still raining here this morning, and a there WAS a miraculous win:Valid for Wednesday morning at 5 AM AST. This is the rain accumulation in the prior 6 h indicated by the area of green.Valid at 5 PM AST, Christmas Day. This follows a short break of several days, a break in which people get lulled into thinking its the end of the rainy spell, but they would be so WRONG! The rain shown here (green areas) is that rain the model believes has fallen in the prior 12 h (the period of rain lowers in resolution as the model gets farther away from its starting point; 6 h has become 12 h of rain areas.)
Go here to see them all, from IPS MeteoStar again. Too many rain panels; too little space. Quite the Big Bopper at the end of the run, too, on New Year’s Eve! One now wonders if after all the drought we’ve had, the sunny, comfy days, we’ll hear, after the next two to three weeks go by, complaints about how wet and cold its been? Humans: we’re like that. Me, too. I like complaining, especially about sound walls.
In sum, we are in a “bowl game”, a “trough bowl” where storms will be collecting off and on for the foreseeable future.
Be ready! It is the author’s experience that in some cases like this, the storms over a period of weeks, intensity, kind of go through a crescendo of sorts before the pattern changes back to dry again. Hope so. This would be great as an AZ drought buster.
Heard thunder for about 12 h it seemed yesterday, but little came of it. Even the rainshafts looked anemic for the most part for the second day in a row.
Current 24 h rainfall totals from the Pima County ALERT gages here. U of AZ network here. “Coco” for Pima, here.
Got hopeful after a disappointing afternoon when an evening shelf of Stratocumulus with buildups spread westward from the northeast, shown in the first photo. Rain shafts began to appear in the upwind direction as the sun set with occasional cloud to ground lightning strokes, ones that continued until after dark. Those showers grew and then were almost dead by the time they passed over Catalina. So another disappointment. Seems you end up saying that a lot when you’re living in a desert and wanting some rain…
6:58 PM. Looking north6:59 PM. Looking NE.7:33 PM. OCNL LTGCG NE (weather texting example for “occasional lightning cloud-to- ground northeast”).4:48 PM. Got hopeful here, too, looking at this dramatic sky toward Charoleau Gap. But no; instead it went down the Catalinas, didn’t spread southwestward.5:27 PM. This is the same complex, now moving away into TUS. Dumped nearly an inch on the wealthy Catalina Foothills district where they probably don’t even need it because they can afford so much irrigation. It had missed us completely. I included this one with lightning because sometimes it seems like you are a people that enjoys fireworks more than a lecture about how graupel forms.
That Enviro Can model isn’t going to win a Gold Medal, another clever play on the Olympic Games now underway in London, with its forecast track for Hector-Ernesto. In our last episode, the Enviro Can mod had H-E drifting northward in a timely manner, and it had been that way in model run after run, so that portions of its remnant produced significant rains in southern Arizona.
The medalist in the H-E track forecast? The USA! WRF-GFS model. It had tropical storm Hector-Ernesto staying far away until it was dead, drifting glacially northward off Baja until it disappeared (as it is shown to do today) with only modest effects here. That USA forecast was better forecast all along.
We just did not get that upper level trough along and off the West Coast, required to steer H-E rapidly northward before it faded over the cool waters off Baja.
The good news is that there is no real droughty days ahead either, which means a steady diet of scattered thunderblusters for another week or so, and if we can get the cloud bases down from 14,000 feet above seas level to 8000-9000 feet (at the top of Ms. Lemmon), we could be back in the 1-2 inch rains in those scattered intense rainshafts. This morning’s sounding from TUS suggests they will be a couple of thousand feet lower than yesterday! Yay!
A quite active day is forecast for us today, beginning in the early afternoon rather than mid to late afternoon as has been the case. The first shower/Cumulonimbus cloud is forecast to form today on the Cat Mountains is by 1 PM, hours earlier than prior days. That would go along with the 5 AM sounding just in which has is more moist than previous days. Note that last night’s model run would not have had this new data.
So, chance of a hard rain in the afternoon if we’re lucky. But what could be really nice is that rain (in the model) continues here off and on overnight at a moderate rate, pretty unusual.
Fingers crossed that the “initial conditions”, the starting point for lat night’s run, are accurate, one of the biggest bugaboos in our models.
For a few minutes yesterday afternoon, it looked like some unexpected rain was trucking over the Cat Mountains from the east-northeast late yesterday afternoon. No one could blame you for getting your hopes up and misleading your neighborhood by saying it might rain in half an hour. Those clouds rolling in from the Catalinas (shown below) were great sights for soaring eyes, ones that look to the skies all the time for rain.
5:16 PM. What’s this! Looks like the old Charoleau Gap storm is coming.5:16 PM. Good base all along the Catalinas, nice and solid-looking5:57 PM. Bottom of those weak Cumulonimbus clouds have evaporated, leaving moslty virga, and a sprinkle that reaches the ground over there by those mountains but not here.
But within the hour, the clouds had broken up, and the shower they produced was reflected by a faint rainbow. Rainbows to the east and northeast are often precursors of rain and wind moving into Catalina. Here is the sad remnants of those albeit weak, Cumulonimbus clouds with their feint rainbow, one that was not followed by one drop of rain here.
A big patch of Cirrus kept the temperature down some during the first half of the day, and so our Cumulus were behind in development compared to areas around us. Here is that bad Cirrus spissatus in case you missed it, that which hung over us so long.
It was quite visible even in the visible satellite image all morning. When it shows up there, you can bet that the Cirrus in that image is thick enough to produce shading and mess up the development of Cumulus under and around it, particularly on marginal rain days like yesterday.
Much Cirrus is virtually invisible in visible satellite imagery; get it? You can see it from the ground (i.e., its visible), those thin wisps of Cirrus, but try to find it in a visible satellite image! This whole line of reasoning and befuddled exposition here reminds me of that Science knee-slapper of a few years ago; that article entitled, “Where are the invisible galaxies?”
1:49 PM. Cirrus spissatus, sitting there doing nothing, but wrecking out Cumulus clouds.
Today?
Raining lightly now at 5:25 AM! Yay. A night stalker mass of rain is moving into TUS now as I write. They don’t usually like the daytime and fade as the sun rises in the sky. Sprinkles, very light rain showers (and as always pointed out here, quite emphatically I might add, “sprinkles is not DRIZZLE, dammitall”, to be a little colloquial there!).
Let’s hope this heavy cloud cover we have now (5:30 AM), which you could call, Altocumulus opacus and castellanus due to its height above the ground (its at about 11-12,000 feet above the ground and has turrets here and there). But, to get a little pedalogical you could label it in your log book as Stratocumulus, perhaps with the appendage, castellanus, since turrets are present–those are what’s causing the sprinkles/light showers.
Sunset was nice….
U of AZ mod shows this is our best day for a significant rain, some of that this morning, and some arises later with those afternoon and evening giants we get around here. Hoping so. Tomorrow is supposed to be drier.
Of course, alluding today in the title to the great western movie with John Wayne…
Every which way you looked yesterday afternoon, there was a great rainshaft. 1.85 inches fell in one hour at Picture Rocks Community Center yesterday afternoon, 2.01 inches total. Several stations around the county had another 1-2 inches yesterday. You can see the Pima County rain lineup here. Seems the great amount in the Catalinas was about half an inch in a gage at Samaniego Peak. Probably twice that between gages up there in the hot spots, where the best columns of rain fell. Also, it would be good to examine our U of A rainfall network today, too, for some jumbo totals. Values are being added during the morning hours as a rule.
Catalina? Well, a measly 0.05 inches fell here after 7 AM until this morning from side-swiping Cumulonimbus clouds, though Sutherland Heights did receive a more respectable 0.28 inches–just measured it. . So, if you were outside yesterday, you saw heavy shafts of rain all around, but none developed over us (the best kind), or moved in here.
But, then, 1.85 inches in an hour, probably most in a shorter time than that, might be “counter-productive”; might make Catalina into a news story, and not a good one… So, I’d better watch what I wish for.
Here are some views of yesterday’s “clouds and columns” of rain yesterday. And, as has been the case, the day started with heavy layer clouds, Stratocumulus and Altocumulus, and a nice, but very brief sunrise “bloom” shown below:
Once these clouds thinned by late morning, Cumulus began to surge upward over the Catalina’s, and reflected an usually strong east-southeast wind just above mountain top levels by trailing over Catalina from Mt. Lemmón. These reached the ice-forming level (read, began to produce rain at the ground) in a series of showers and thunderstorms by 11:30 AM (2nd photo).
Looked, too, like another tube (funnel cloud) at 3:48 PM yesterday off in the direction of Marana, but I’ve posted so many of late I thought I would just post it at the bottom of these more interesting photos.
11:03 AM. Cloud “street” off the Catalinas.11:31 AM. From Mt. Lemmon to us, straight overhead!1:01 PM. Repeated showers STILL trailing off the Catalinas! But not over us.
1:01 PM. First major-colossal dump occurring N of Park Links Road. Note bit of rain falling from overhang cloud from the prior photo. Tops shearing off; rain-producing part (top of photo) has no underlying cloud for the drops to grow in as they fall, so no collosal-major dump. Did start thundering about then, though
1:16 PM. This is so pretty! Now, one of those turrets has leaped upward, more or less straight above the bottom of the cloud, and now, though a small one, a major-colossal dump on the Cats. I love these scenes here!
2:36 PM. Its gonna miss Catalinans, BUT, this is where you want to be under. Look at that downspout! That whole cloud is loaded with precip, and the Big Boys are dropping out now, and just before this, the largest ones able to overcome the updraft so its especially great and exciting to be under a cloud like this just as those strands of rain/hail drop out. Also about the time such clouds get “plugged in” and send light daggers to the ground, as in this case.
2:41 PM. Its just FIVE minutes later! You probably haven’t even gotten in your car yet to try to get over there. Its too late. This was a one dumper and gone. Faded away into just a residual ice cloud.
2:57 PM. Done, cooked, fried. Without the flanking clouds piling up into new turrets that reach the ice-forming level, all you have after just 20 min or so, is this sad sight of a dying, once proud Cumulonimbus cloud. Rain here likely due to aggregates of ice crystals called snowflakes if you up there flying in them.
3:04 PM. What was truly remarkable about yesterday was that those smallish Cumulonimbus clouds just kept on generating over and over again off the Catalinas. Very unusual, and was a measure of how unstable, how easy it was, for the clouds to surge upward yesterday.
3:47 PM. Another one! Unbelievable. Like the bunny, going and going and going.4:01 PM. Its practically nighttime, cool, overcast, not good for Cumulus, and yet look how this little group was trying so hard to be a rain cloud. Sadly, they didn’t make it. Have never seen such tall thin clouds like this here in this kind of environment, that’s why I posted it.3:38 PM. Likely funnel cloud just above bright spot, the longer filament, not the nub from the cloud base in the foreground, but from the next base farther away.
Moisture continues to revolve into Arizona from the southeast and so it would appear a similar day is in store for us. Oh, goody.
