No NWS sounding from the U of AZ Weather Department yesterday afternoon, so’s we can’t really tell with solid data what the temperatures of yesterday’s frosty clouds were.
However, with a max here in the Heights of Sutherland of 71°F, and with a dry adiabatic lapse rate to the bottoms of the clouds (as is always the case on sunny afternoons with Cu), if we estimate how high the bottoms were with any accuracy we can get that bottom temperature.
You already know as a well-developed cloud maven person that they were WELL below freezing which could see by noticing how far the snow virga extended below the bases of the Cumulus, at least 3,000 feet. and more from the larger clouds later on. So we have something,
Let’s say bases were at 14,000 feet above the ground over Catalinaland–they were way above Ms. Mt. Lemmon at 9,000 feet which you could probably tell. That would make the bases at about 16,000 to 17,000 feet above sea level in the free air, pretty darn high above us.
From a ground level of 3,000 feet, and with the dry adiabatic lapse rate of 5.4°F per 1000 feet, that would make the cloud bottoms a cold, cold, -2°F, or about -17° to -18°C! COLD! Then, tops, of clouds only 3,000 feet thick (about 1 km), would be -28° to -30°C (assuming a mix of the dry adiabatic rate with the “moist adiabatic” rate, given yesterday’s conditions, or about 4° per 1000 feet, “plus or minus.”
Addendum–corrections, hope nobody see’s ’em:
Later analysis and the next morning’s NWS sounding from the U of AZ suggests that bases were closer to -10°C because they were not as high as CMP estimated. Rather they were closer to 12,000 feet ASL. Tops would not be quite as cold, too, more like -25° C and colder in the deeper clouds, plenty cold enough for ice in even the small clouds, and for the long snow virga trails.
Below, some samples of Frosty the Cumulus (Cumuli, plural):
1:22 PM. Small Cumulus (humilis and fractus) begin to form.
3:40 PM. By mid-afternoon, the slightly fatter Cumulus clouds (mediocris) start showing ice crystals coming out the downwind side, which is what that bit of haze is above the cloud outline.3:41 PM. An ice haze is seen here, too, in the dissipating remnant of a humilis-sized Cu on the left edge, center.4:10 PM. Ice is appearing just about everywhere now as the air aloft cools a little more, and the Cumulus deepen upward some. The clouds are likely no deeper than about 3,000 feet or about 1 km. Tops, using the in-cloud lapse rate, typically a little less than the dry adiabatic rate, would be a frigid -27° C (-17°F) or so, which readily explains the ice-behaving nature of yesterday’s shallow Cumulus. Even deeper clouds formed later in the afternoon and evening hours. This image not left “blank” but has explanatory writing on it.5:23 PM. Raindrops from heavy virga were beginning to reach the ground in several areas as evening approached. Overnight, a few fell on Catalina! These Cumulus complexes were likely more than 2 km thick, 6600 feet) topping out at temperatures well below -30°C (-22° F)
Not much ahead now. Maybe a few more frosty Cu will form today… before things dry out and heat up.
No, this is not about Bonanza, the TEEVEE show, “Hoss”, or any of those ranching people, though that might be more interesting than a blog about clouds, gray ones. First of all, the word, “bonanza” would be capitalized (its not on my view of this edit, FYI) if this was a blog about it. Second, there was no “Bonanza” episode about Stratocumulus and drizzle, another clue.
Your cloud diary, for those of you still reading this blog:
8:34 AM. An orographic layer of Stratocumulus tops Sam Ridge while a separate higher layer covering the whole sky sits on top of it. Neither one seem to be able to produce precip, ice or “warm rain”–precip without ice.8:34 AM. Stratocumulus. Light rain is falling from them on the horizon. What does it mean? Those clouds over there are just that bit thicker, tops higher and colder. Could be a warm rain (no ice involved) or a case of “ice multiplication”, a still continuing mystery in the cloud and precip domain where more ice forms in clouds than we can explain. Mostly occurs when the cloud top temperatures are higher than -14°C to about -4°C. Ice crystals can be in tremendous concentrations in such clouds but we don’t know quite why yet. So, models that forecast rain and snow, as good as they are today, could be that bit better if they could accurately the ice in clouds in that cloud top temperature range I just mentioned a few paragraphs ago. That’s probably the biggest payoff for really understanding how ice forms in clouds. At the University of Washington, me and Peter Hobbs were reporting that the consensus theory on how ice formed in clouds was not capable of explaining what we were finding in the clouds we sampled with our aircraft. There was too much ice in clouds, and it appeared too fast. We were on the outside looking in and our whole body of work was criticized as being wrong by two of the great professors of ice-formation in clouds, Alan Blyth and John Latham in 1998. They used our names in the title of the article, too, “the glaciation papers of Hobbs and Rangno.” I sent a copy to mom. This is what happens when you’re not part of a consensus, you eventually get criticized royally because no one believes you, they think without commenting about it that your work is bogus. At the same time, it was truly GREAT that Blyth and Latham took time to look into all of our work since we scientists don’t do enough of that kind of thing, look into the work of others we suspect might be wrong. But over the years, the concensus about how ice forms in clouds has weakened and new factors are being touted as important players like drizzle drops that fragment or explode when they freeze because at certain temperatures an ice shell develops on the outside of a freezing drop, and then when the water farther in freezes and tries to get out because it wants to expand, it breaks the ice shell, and maybe spicule or ice splinter comes out helping to produce extra ice we call secondary ice particles since they didn’t form on an “ice nuclei”, something we have a though time measuring anyway. Fragmenting drops as they freeze has been known about for decades, but now its being thought that maybe a lot fragments result, not just a few as was thought before. So those extra ice crystals end up creating concentrations of ice crystals we can’t quite explain in clouds here even in 2018, such as those ones over there that were raining north of Saddlebrooke to bring us full round in this photo. Caption too long? Let us not forget that this site originated the practice of novella-sized captions. I think many of you forget that a picture is worth a thousand words of caption, too. Here, we’ve only managed a few hundred.10:13 AM. Still raining way over there NE of Saddlebrooke and Bio2 if you look carefully, lower right. Can there be a better “classic” photo of Stratocumulus? I don’t think so. Cloud bases still running about the level of Sam Ridge, or about 3,500 to 4,000 feet above the ground.10:05 AM, maybe. Stratocumulus clouds spewing drizzle precip roared out of the west in a band, now enveloping the Catalinas toward Pusch Ridge. Drizzle is pretty rare in Arizona, so I hope you noted it in your diaries yesterday. Means the clouds overhead have low droplet concentrations, and the larger drops are greater than about 30 microns in diameter, which are those sizes that when they bump together they can coalesce into a much larger drop that collides with more and more drops to form ones that can fall out of the cloud instead of just hanging around up there not doing much. We call that process the “collision-coalesce” process of rain formation, or “warm rain” process, one that doesn’t involve ice. The formation of ice almost never results in drizzle, hence (is that still a word?), why CMP thinks it was a warm-rain process yesterday over there. Also, drizzle is often think enough to make it look like its a snow shaft, which is what we see over there, too. But we know the freezing level was really high yesterday, so it can’t be snow over there. Nor are the clouds Cumulonimbus ones that CAN produce dense shafts.
Well, let’s move ahead to sunnier conditions, those pretty scenes we see on the mountains when a storm begins to clear out.
12:27 PM. As the Stratocumulus broke up, you got a glimpse of the deeper clouds north of Oracle that had been, and likely were still raining. Estimating depth here at about 2 km, or 6600 feet. With bases at 4,000 feet above ground, that would put the tops at only around 11,000 feet, too warm for ice since it would barely be below freezing at that height. Will check now to see if that statement is true. Actually, the soundings from the U of AZ make it a little more ambiguous than what I was thinking about too warm for ice formation, and so there’s no point in showing those soundings where people might question what you just said.1:19 PM. So pretty. I am a lucky man to see scenes like this so often.1:29 PM. A cloud street with this fat boy formed off the Tortolita Mountains and it passed overhead of Catalina! I wondered if some big drops might fall out since it would be a Cumulus congestus if you could see it from the side, and with “warm rain” having fallen earlier, there was still a chance that the drops in this guy, toward the tops, would reach sizes where they coalesced into drops.1:29 PM. Nice. One of our photo niches is cloud bases, and here’s one of the best. Am waiting outside for big drops, not Godot. Can’t go inside because they might only fall for a few seconds or minutes, it surely won’t be shaft. And what if no rain had fallen earlier? I might need to report a trace.1:41 PM. It wasn’t too much longer the drops began to fall, finally thinking to get a photo in case no one believed me that rain had fallen from that cloud.2:11 PM. Cumulus humilis and Cu fractus are all that remain of the gray skies of morning.3:59 PM. Just enjoy.6:37 PM. The sun, completing its weary journey around the earth, finally goes down.
The End
PS: The agonizing delay from typing then seeing words appear 5-10 s after you stopped typing, disappeared when I jettisoned Firefox for Safari. So, all these months of agony, were due to a Firefox bug, not a WordPress or GoDaddy hosting service problem. Unbelievable. This problem I think began when I downloaded the latest version of Firefox, which also came loaded with pop up ads and web site diversions it previously was free of. Dummy me never connected it to the venerable Firefox web browser. So, Firefox has been trashed from this computer!
10:56 AM. Things looked promising except clouds like this over the Catalinas moved away from us. And no Cumulonimbus clouds formed over them, but rather downwind toward and beyond the town of Oracle late in the afternoon.3:30 PM. Not much going on; a very thin veil of ice was dropping out of these clouds, once the tops of the Cumulus cloud to the right and out of view. Hope you caught it. There weren’t very many ice displays until later.5:31 PM. That blasted haze/smoke layer is still evident! at the center is a glaciating turret, giving hope this whole cloud cluster could erupt into something. The model from the overnight run suggested just such an event!6:09 PM. Hah! A shower at last! And the movement is in the general direction of Catalina!6:36 PM. Stupendous sunset view, and this cluster is getting closer!6:42 PM. Zoomed view near last light. Portions of this complex consisting of a weak thunderstorm did pass over, but no shafts, just a few drops for a “trace” of rain. By this time bases had risen to about 14,000 feet above sea level, or about 11,000 above Catalina and near the freezing level, so a lot of evaporation on the way down for those poor droppies.
Last call for Cumulus clouds today, maybe a distant Cumulonimbus top off to the north. Then one of those long clear and dry spells of fall gets underway….
One passed over at 9:19 AM with a hard multi-second, surprise rain shower. One person reported a couple of graupel, or soft hail particles. Tipped the bucket, too; 0.01 added to our Sutherland Heights storm total. Its now at 0.23 inches. Of course, there was no damage, but putting that word in a title might draw “damage trollers”, increase blog hits….
The rest of the day was clouds withering, getting mashed down on tops as bases rose and tops settled back, then suddenly, about 3:30 PM, small areas of ice crystals began to show up in a couple of spots, and, boy, did things take off after that. Tops were lifting to higher temperatures, likely due to an approaching trough, one that otherwise is too dry to do much else.
Honest to goodness cold, wintertime Cumulonimbus clouds formed, though not very deep ones. Probably of the order of 2-3 km thick is all (eyeball estimate).
But with our cold air aloft, tops were well below -20° C (4° F), lots of ice formed in them and produced streamers of ice and virga across the sky, and in tiny areas, the precip got to the ground.
And with “partly cloudy” conditions, there were lots of gorgeous, highlighted scenes around the mountains.
Let us review yesterday’s clouds and weather and not think about the future too much, starting with an afternoon balloon sounding temperature and dew point profile from IPS MeteoStar:
The Tucson balloon sounding (“rawinsonde” in weatherspeak) launched about 3:30 PM yesterday. Takes about an hour to reach 60,000 feet, but goes higher. Cloud bases were just about at the top of Ms. Mt. Lemmon. Tops were only around 18,000 feet above sea level, but were extremely cold for such small clouds. Hence, they were only about 9,000 feet thick at their maximum.
So what do clouds look like when they have tops as cold as -28°Ç?
Well, I really didn’t get a good profile shot of those clouds, they were either too close, obscured by other clouds, or too faraway, so instead let us look at two dogs looking at something as a distraction:
4:11 PM. Dogs observing a plethora of glaciating Cumulus clouds, transitioning to Cumulonimbus.
Well, let’s start this when the ice first appeared in a cloud, much later in time than what was thought here yesterday morning. If you logged this “first ice” you are worthy of a merit, a star on your baseball cap:
3:24 PM. FIrst ice of the day, finally, spotted on the SW and WSW horizon in two little areas. The file size is huge so that you can see it for yourself. I had just about given up on ice in clouds, Notice, too, how small the clouds are at this time.
Well, while flawed from a cloud profile sense, here’s what they were looking at, it was the best I could do:
4:19 PM. Note sunlit shower reaching the ground. The hazy stuff is ice crystals, a lot of them all over the place.4:22 PM. A close up in case you don’t believe me that the rain was reaching the ground. I sometimes find that credibility is lacking here.4:39 PM. Eventually a cluster of precipitating clouds developed near the Catalina Mountains and here are dropping snow and graupel trails.
Let us go zooming:
4:39 PM. Shaft up close. That dark, narrow line in the middle is without doubt a soft hail (graupel) strand. THere might be others, but this one is obvious. The “verticality” is due to faster falling particles comprising that strand, which graupel are because they are ultimately snowflakes that have captured cloud droplets on the way down, making them much heavier than just a snowflake.4:45 PM. Just light snow falling out here on the Catalinas, no real “verticality” in this shaft, which would be a sign of graupel falling out.4:46 PM. An opening allowed this zoomed cross section of a cold, wintertime Cumulonimbus (capillatus) cloud streaming a shield of ice and virga downwind. On the left sloping-upward part, the Cumulus turrets still contain liquid droplets (have that ruffled, hard look associated with the higher concentrations that go with droplet clouds compared to all ice clouds). Sometimes, in spite of the low temperature, here, from the sounding the top is likely approaching the minimum temperature of -28°C, droplets can still survive for a short time before freezing, giving way to lower concentrations of ice crystals. That appears to be the case here at the tippy top. of the cloud in the back What is interesting here, an enigma, is that the foreground cloud in front of the cloud I was just discussing, is clearly all ice from the smallest element to its top and mimics the cross section of the background cloud. Could it be that its simply older and ice generated in the colder regions has permeated the whole cloud?
Below, diagrammed:
Same photo with writing on it since the written explanation didn’t seem very satisfactory.5:07 PM. Graupel in the Gap (the Charouleau one). Well, maybe its a little beyond the Gap, but it sounded good to write that.. This started to fall out of a Cumulus congestus transitioning to a Cumulonimbus. The first particles out the bottom are always the heaviest, hence, graupel or hail.
Looking elsewhere, there are snow showers everywhere!
5:08 PM. Nice shafting over there near Romero Canyon. Pretty straight up and down, so likely has a lot of small graupel in it.5:08 PM. Looking down Tucson way, this is NOT a graupel shaft, but rather gently falling large snowflakes.. Sure the particles are large, but look at how they’re just kind of hanging there getting mixed around by a little turbulence, almost forming a mammatus look. There are likely aggregates of dendrites, fern-like ice crystals that grow like mad around -15° C, and because of being complex forms, often lock together when they collide. Its not unusual to have 20 or more single stellar. dendritic crystals locked into a single snowflake. Where the bottom disappears, likely around 3000 feet above sea level, is where those big aggregates are melting into rain drops.5:10 PM. Interrupting the tedium with a nice neighborhood lighting scene as a sun poked between clouds. We’re not completely cloud-centric here, but close.5:26 PM. This strange scene of a very shallow snow cloud, completely composed of ice and snow, obscuring the tops of the Catalinas, but being very shallow, hardly above them may explain the cross section enigma. The snow cloud here is all that remains of a much deeper cloud that converted to all ice, then those crystals just settling out, the whole cloud dropping down as a snow flurry. It may well have been as deep as the cloud top on the left or higher before converting to ice and just falling to the ground “en masse.” Or is it, “en toto“? What makes this odd is that there is usually some “cloud ice” (ice particles too small to have much fall velocity) at the level from which the precip fell from. You don’t see that here; just a belt of light snow. Maybe this is why there was that shallow, glaciated cloud in the Cumulonimbus cross section shot….. That shalllow cloud was not a new portion, but rather a tail dragger like this stuff, once having been much higher and was actually ice settling out, not new rising, glaciated cloud. From the back side, you can see that this ice cloud would appear to slope up if viewed from the east instead of the west like our cross section iced out cloud. Setting a record for hand waving today. IS anybody still out there? I don’t think so. Maybe I need another dog picture….5:34 PM. Here’s the last of that unsual snow cloud as its last flakes settled to the ground.
The day concluded with a very nice sunset:
5:53 PM. Sunset color with shafts of snow turning to rain down Tucson way.
Now, the long dry spell… Break through flow from the Pacific under the “blocking high” eventually happens about a week away now, but more and more looks like that flow might stay too far to the north of us, rather blast northern Cal some more, and not bring precip this far south. The blocking high needs to be in the Gulf of AK, but now is being foretold to be much farther north…
The End, gasping for air here. More like a treatise than a quick read!
3:55 PM. Rainbow fragment and solar home, an extraordinary combination.. It was yesterday’s visual highlight. Yours for $1995.95. And, if you order now, we’ll throw in a second, exact copy of this extraordinary, magical scene FREE!
Here’s a nice one from the day before as the clouds rolled in, starting with Cirrus and Altocumulus, lowering to Stratocumulus later in the afternoon.
Yesterday’s clouds; an extraordinary day with a little drizzle amid light showers
Hope you noticed the true drizzle that occurred yesterday, namely, fine (larger than 200 microns, smaller than 500 microns in diameter), close TOGETHER (critical to the definition of “drizzle”) drops that nearly float in the air. They may make the least impression, or none, when landing in a puddle.
When you see drizzle, you have the opportunity of chatting up your neighbor by educating them informally to what drizzle really is (many, maybe most, TEEVEE weatherfolk do NOT know what “drizzle” is, btw), and 2) by telling your neighbor, if he/she is still listening to you, that the droplets in the clouds overhead must be larger than 30 microns in diameter, or better yet, “larger than the Hocking-Jonas diameter of 38 microns, at which point collisions with coalescence begins to occur” and “drizzle is not produced by ice crystals in the clouds overhead; they’re not enough of them to produce ‘fine, close together drops.'” Your neighbor has likely left the building at this point, but, oh, well, you tried.
Here, in Arizona, shallow clouds, such as we had yesterday, hardly ever can produce the broad droplet spectrum in which clouds have droplets larger than 30 microns in diameter. Its because this far inland from the ocean, where the air is very clean, the air has picked up natural and anthro aerosol particles that can function as “cloud condensation nuclei” (CCN). As a result of ingesting dirt and stuff, clouds have too many droplets here as a rule for the droplets in them to grow to larger sizes. They’re all mostly less than 20-25 microns, sizes in which even if they collide, they can’t coalesce.
In “pristine” areas, if you go to one, such as on a cruise out in the oceans, droplet concentrations in clouds are much lower, and even a little water that might be condensed in a shallow cloud can produce a broad spectrum, one that extends to droplet larger than 30 microns.
So even little or shallow layer clouds can precip over the oceans, produce drizzle or light rain showers (in which the larger drops are bigger than 500 microns in diameter). Of course, here we recall that the (whom some consider “villainous”) geoengineers want to stop drizzle out over the oceans so that clouds have longer lifetimes, are darker on the bottom, and reflect more sunlight back into space.
Those guys can be lumped into the same ilk as those who want to change the color of the sky from blue to whitish or yellowish by adding gigantic amounts of tiny particles in the stratosphere, again for the purpose of cooling the planet! Unbelievable. Please ask before doing this!!!
A Pinatubo sampler for what “geoengineering” would do to our skies, say, sunsets in particular. I took this photo from the University of Washington’s research aircraft in 1992 off the Washington coast in onshore flow. But we saw these same sunsets, sunrises, yellowed by the Pinatubo eruption of June 1991 everywhere we went, including in the Azores in June 1992.
OK, pretty boring, whiney, really, so inserting picture of a nice horse here to make people feel better if you’ve been depressed about what our scientists have been pondering to do about global warming other than controlling emissions:
8:57 AM. Zeus. Led cloistered life for 13 years; likes to bolt, now that he’s getting out on the trails.7:40 AM, yesterday, Dec. 31st. The low hanging Stratocumulus clouds, about 1500 feet above Catalina, and the mountains had a bit of an orange tinge. It was probably due to sunrise color on a separate much higher layer.
Later….drizzling Stratocumulus, same view:
10:30 AM. Stratocumulus praecipitatio, if you want to go “deep” into cloud naming. “Stratiformis”, too, covers a lot of the sky. Note misty-like view, lack of shafting.12:48 PM. More Stratocu P., an example of those clouds in the distance that kept dropping little and light rain showers on Catalina.1:01 PM. Highlighting amid the RW– , (weather text for “very light rain showers”). Stratcu P., with maybe Stratus fractus or Cumulus fractus below. The shadowed, dark shred clouds in the mddle would be Stratus fractus IMO.3:55 PM. Zooming in on that pretty rainbow. You know, this is a cloud heaven here. I hope you all appreciate it! Maybe that’s why I get upset over “geoengineering” and changing the sky anywhere.3:57 PM. Between showers, but new ones erupted upwind. This one have a shaft, implying a higher cloud top than the prior, non-shafting clouds that brought us semi-steady RW–.
The second extraordinary thing about yesterday was that the top temperatures of these clouds was around -10° C (14° F), temperatures that ice does not form act as a rule in Arizona. To get ice at temperatures that high, you also need larger cloud droplets, and they have to occur in the -2.5° C to -8° C range. In this range, it was discovered that falling ice crystals, mostly faster falling ones like “graupel” (aka, soft hail) when colliding with larger drops, ice splinters are produced. The cloud droplets must be larger than 23 microns in diameter in THAT particular temperature zone, something that would occur more often in our warm, summer clouds, but would rarely be expected in our winter ones.
Why?
Again, it goes back to clouds in inland regions ingesting lots of natural and anthro aerosols that cut down on droplet sizes in clouds (by raising droplet concentrations in them). Our recent rains have helped cut down on that process on ingesting dirt, for sure, and was a likely player yesterday. Furthermore, our winter clouds are moisture challenged relative to the summer ones with their tropical origins and high cloud base temperatures, a second reason not to expect larger droplets in our winter clouds.
Here is the TUS sounding with some writing on it for yesterday afternoon from IPS MeteoStar. (Satellite imagery was also indicating warmer than usual tops for precipitating clouds yesterday.):
The TUS balloon sounding (“rawinsonde” in techno speak) launched at about 3:30 PM yesterday afternoon. Balloon rises at about 1,000 feet a minute, FYI. Typically they pop up around 100,000-120,000 feet! Instrument package is parachuted down so it doesn’t conk somebody on the head. Sometimes they are found and returned to the NWS and re-used! How great is that?
Here’s the punchline: If clouds are drizzling, then they are ripe, if the tops get to lower temperatures than about -4° C for what we’ve termed “ice multiplication” or “ice enhancement”. A very few natural ice nuclei at temperatures between -4° and -10° C, say, starts the process, those forming “soft hail” which then leads to ice splinters. This is the leading theory of this anomaly of ice in clouds at temperatures only a little below freezing, if you think 23° to 14° F fits that definition.
There are exceptions where this process did not explain the ice that formed at such high temperatures, so standby for further elucidation about how in the HECK ice forms in clouds at some point in the future.
As usual, no time to proof, so good luck in comprehending what’s been written.
The weather just ahead:
The second main rainband is just about here at 9:25 AM. Cloud tops will be deeper and colder than in the prior rains, raising the possibility of some thunder today, and maybe another third of an inch of rain. Watch for an windshift line cloud (“arcus” cloud) might well be seen today. That’s always dramatic and exciting here in Catalina cloud heaven.
A very few small, isolated drops fell between 4:50 and 5 PM here in Sutherland Heights from what appeared to be nothing overhead. You’d have to be really good to have not been driving, and to have anticipated the possibility (by recognizing ice in upwind clouds) and then having observed it. You would be recognized, given some extra adulation, at the next cloud maven junior meeting if you did observe it, that’s for sure.
So, a long blog about anticipating and observing a sprinkle of rain (RW—, “RW triple minus” in casual weatherspeak or text).
We start with some nice, but inapplicable to our main story photos from yesterday.
3:14 PM. Another one of those, to me, memorable, dramatic shots just because of cloud shadows on our pretty mountains caused by Cumulus humilis and mediocris clouds; Cirrus uncinus on top.3:15 PM. Pretty CIrrus uncinus, “Angel’s hair.”3:15 PM. Looks like a cloud street off the Tucson Mountains, one that streamed toward Catalina. Hope you were “unbusy” enough to notice it. Its a pretty common one here when the lower level winds are out of the SSW, and the clouds shallow.3:50 PM. Shadow quirk. The cloud shadow follows the terrain line. Wow. Never seen that before, but I suppose if you had an infinite number of monkeys watching, they’d something like this all the time. Maybe they’d type out some Shakespeare as well in time.3:54 PM. While busy watching the cloud-sahdow dappled mountains, some honest-to-goodness Cumulus congestus arose in a line to the southwest! Not at all expected! Looks like they’re tall enough to form ice, but don’t see any. Will take too many photos to see if any develops though.3:56 PM. That poor turret that first extruded from this line (center raggedy one) is being ravaged by “entrainment”, that cloud killing process wherein the surrounding dry air gets in and kills off the droplets. Pretty sad when you think about. It also shows you just how friggin’ dry the air was just above the main tops. No ice visible here.3:56 PM. Let’s zoom in to be sure. Anyone saying they can see some ice in this is either an ice-detecting genius or just plain lying. BTW, that turret on the left, partially visible, is much taller, so its got a good chance to convert to ice.
3:58 PM. Now even little tiny babies can see the ice that formed in that now dessicated turret. This means some rain fell out of it! Wow, did not see that happening today.3:58 PM. Pulling back to grab the whole scene, those Cumulus congestus clouds converting to small Cumulonimbus clouds that will bring those few tiny drops to Catalina in an hour even as the dry air up there wasted them. Real cloud mavens would be thinking about the possibility of rain here, seeing the ice form in clouds upwind of us, that right at that time! Congratulations!4:09 PM. Doesn’t look that great now, but areas of ice visible, and its heading this way with a light shower falling out of it! Maybe we’ll pick up another trace! But what cloud name would you put on this scene? Well, its kind of embarrassing to call them “Cumulonimbus”, but we do have a suitable moniker for weakly-producing Cumulus ice clouds with a little precip, Cumulus congestus praecipitatio. Yep, that’s the name I would use here since the rain is reaching the ground (is not just producing virga).4:30 PM. Code 1 rain shaft, a transparent one. We’re going to a LOT of trouble for a trace of rain here! But, you should have been really excited by this time. The possiblity of rain is just minutes away, but you’ll have to be outside to notice it!4:40 PM. Drawing back to look at the whole scene, which is not that great. Bottom of sprinkle cloud has evaporated leaving that big patch of ice, left side of photo. Can the sprinkle heading toward us survive? Your heart probably was really pounding at this point since you wanted to see some drops so BAD, report that trace the next day, one that maybe only you would have noticed.4:47 PM. Three minutes to first drops, though here no drops would be reaching the ground from the condition the cloud is in now, its too high, just really anvil ice, and the ice crystals too small, The drops that are going to be intercepted are surely the last ones reaching the ground, the top of the sprinkle shaft, above which there are no more drops.4:55 PM. Drops are collecting on the windshield a few hundred yards from the house with almost no cloud aloft at this point! A trace of rain has been logged!
The End
(What about those gorgeous Cumulus congestus and Cumulonimbus calvus clouds over toward and well beyond Charouleau Gap about this time? Maybe later or tomorrow.)
Some apocalyptic cloud scenes can be Cumulus that explode suddenly into Cumulonimbus, and Cumulonimbus clouds with their foreboding (unless you live in a desert) rain shafts, and their predecessor shelf clouds like “swirly dark Stratocumulus”, and arcus clouds, the latter, a lower line of clouds just above and a little behind the wind shift at the ground, usually just ahead of the main rain shaft. While we didn’t get to see an arcus cloud yesterday, we had some dramatic swlrly dark Stratocumulus clouds to scare us. I say “swirly” because if you looked up yesterday evening as they passed over, you would have seen rotation in them.
These can combine, as they did yesterday, to make you think someone might drop out of the clouds and fix the world1. See those scary photos below, way below as it turns out.
This monster collection of Cumulonimbus clouds (“mesoscale convective system” or MCS in weather lingo) with swirly shelf clouds preceding it barged over Catalina later yesterday afternoon after it appeared that not much was going to happen all day. Heck, there wasn’t even a decent Cumulus over the Catalinas until after 2 PM!
The result of this system slamming Catalina was the usual strong preceding winds roaring down from Charouleau Gap way and points north or northeast. The winds were not as damaging as three days earlier.
Then the rain! So nice! Got 0.55 inches of rain here in Sutherland Heights, an inch and half on Samaniego Ridge, and 1.65 inches on Ms. Lemmon.
Worth watching is the U of AZ weather departments time lapse video, especially beginning at 2 min 50 s into it. That’s when the big group of Cbs begins to make its presence known from the east. What is interesting, and what I have not seen before, is that you will see the tops of a thunderhead farther west, that icy part up around 30,000 to 40,000 feet, shoved backwards (back toward the west) by outflow at the tops of the huge incoming system. Very dramatic.
Yesterday’s clouds
1:30 PM. Yawn. Its 103 F, dewpoint 60 F. Baby Cu begin dotting the Catalina Mountains.2:14 PM. Cumulus congestus finally arises within the local cloudscape. Looks like the top is high enough to convert to ice.
Detour: detecting ice in clouds….some practice shots
As the burgeoning cloud maven junior person you, of course, know how important the appearance of ice in our clouds is. You got ice; you got precipitation, which is snow up there, soft hail, hail, frozen drops.
2:19 PM. The declining right side of this cloud has ice in it, but its hard to detect for most observers. Only the BEST of the cloud-mavens could scream out, “there it is!”, before its more obvious to the less gifted CMJPs.2:22 PM. Well, too easy now to see that there’s ice in those little fingers extruding out from the body of the cloud; evaporation of the cloud drops has left the slower evaporating ice “naked” so-to-speak. It also in the higher turret, and would be termed a “calvus” topped Cu, properly, Cumulonimbus calvus, though not much fell out of this one, close to Saddlebrooke.3:31 PM. In the meantime while I wasn’t looking, Mt. Lemmon erupted sending a plume of cloud droplets, higher up, ice, skyward to at least 35,000 feet ASL. Indicated a phenomenal amount of instability afternoon, instability that was about to be realized in a line of mammoth Cumulonimbi.3:49 PM. “Eruption” just about over. Notice how skinny the root is now, AND that the top of the stem of convection is now only about half as high as in the first shot. Like a wild fire plume that has cooled off, the plume height goes down. Still formed ice on the right side, as you SHOULD be able to see. You should also be guessing that those were likely warmer habit crystals, like needles and sheaths. I did, if that’s any help.4:38 PM. Another cloud jack (Cumulonimbus eruption indicating a whole lotta instability), tops probably far above 40,000 feet. A lower portin of the anvil drifts southward toward Catalina. This one was dumping somewhere near the Biosphere 2 landmark. Note that anvil, lower right. That was our incoming major complex of Cum5:17 PM. WOW! This was magnificent, and just one of the many large Cumulonimbus clouds racing toward the Catalina Mountains. This is the one that in the video, the crown of it can be seen forcing the air over us in the opposite direction. Still, it was not certain at this time these storms would make it here. And, this is looking ESE, while the storm movement was from the ENE.5:25 PM. The “Menace of Charouleau Gap”. Many of our worst storms roll in from the ENE, toward Charouleau Gap, and many who have lived here will tell you and this is the archetypical seen for those storms. A sudden blackening of the sky beyond Charouleau Gap. These darker clouds are rarely the ons producing the storms, but are riding a strong NE wind surging toward Catalina, about to produce some mayhem. The winds always arrive before the rain. And, as a few days ago, there are times when ONLY the wind arrives, there is not enough instability aloft to allow the storms to drift past higher terrain without falling apart. On this day, they will make it.5:48 PM. I am going to work this scene over because it is associated with one of the more spectacular storm sequences here in Catalina, one that comes up usually a few times every summer. The anvil outflow aloft is thickening and lowering, and the outrider shallow Stratocumulus are racing out and along the Catalina Mountains. Things are changing incredibly fast and the NE wind is about to hit.6:05 PM. Walking the dogs to beat the rain, The NE wind has hit, the power line wires are howling. The sky continues to darken and look ominous, but….no rain shafts have come over the mountains, a cause for concern.6:21 PM. The shallow clouds ahead of the rain area continue to spread down and out from the Catalinas. A small opening in the clouds allows this dramatic highlight. I like highlights.6:22 PM. Let’s look a little closer at this spectacular highlight. Wow! This is just as good as a bolt of lightning.6:33 PM. Maybe time to get the Good Book out, cram for the finals…. This was really quite the sight, considering it had been so sunny just a couple of hours before. Again, these are fairly shallow clouds riding the outflow winds, now gusting 35-45 mph in Sutherland Heights. The mottled bases here indicate that there is no organized wide updraft to launch them into deep Cumulonimbus clouds at this moment, anyway.6:34 PM. Finally, a major new rain shaft emerges over Samaniego Ridge, upstream of Catalina!6:35 PM. Looks like more and more people are dropping off Word Press as these files are going in pretty easy now.Here, the apocalyptic cloud formation rolls down and out across Oro Valley, with heavy rain just to the left.6:43 PM. A rare sight, wind driven rain streaming off the tops of the foothills of the Catalinas. The winds were likely hurricane force (>64 knots, 74 mph) to do this. Samaniego Peak received 1.50 inches during this storm.7:21 PM. Sunset in Catalina, July 29th. The sun does not have a sharp disk, is rather blurry, because the light from the sun is being scattered by large particles like rain drops which bend the light so that we can’t see the disk’s outline. When its smog, the particles are of the order of micrometers and a sharp disk will be seen because the sunlight is not bent around large particles. I think Einstein said that…7:21 PM. Orange and rainy as sunset procedes as usual.
Only the largest hailstones up there can make it to the ground as such here in Arizona due to our high summertime freezing levels. The rest melt into raindrops, some of which are large enough to reach the ground. Those downpours that suddenly emit from cloud bases were always hail or graupel (soft hail) aloft.
Sometimes in deep stratiform clouds attached to clusters of Cumulonimbus clouds, and with especially moist air from the base of the stratiform layer to the ground, clusters of ice crystals we call snowflakes make it to the ground without evaporating as steady light or very light rain.
Last night as our storm was coming to an end, it is likely that THOSE drops were once snowflakes rather than soft hail or graupel.
The End (finally)
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1Huh. Maybe that wouldn’t be a bad thing. I am very concerned about microplastics (particles 5 millimeters and smaller) in our oceans, resulting from the breakup of larger plastic items we’ve been throwing in the oceans for decades. Seems those tiny particles are getting into everything, including the fish out there! It would be great if someone could get rid of them.
Lot of great scenes on the 18th, but, ultimately with hopes raised for appreciable measurable rain in Catalina, it was a disappointing day. Nice temperatures, though, for May if you’re a temperature person. Only a sprinkle fell (4:15 PM), and if you weren’t outside walking the dogs you would NEVER have noticed it.
Here is your full cloud day1, as presented by the University of Arizona Weather Department. Its pretty dramatic; lot of crossing winds, as you will see, and an almost volcanic eruption in the first Cumulonimbus cloud that developed near the Catalina Mountains.
That blow up was indicative of an remarkable amount of instability over us yesterday morning, one that allowed really thin and narrow clouds to climb thousands of feet upward without evaporating. Usually the air is dry enough above and around skinny clouds that even when its pretty moist, they can’t go very far without the drier air getting in and wrecking them (a process called, “entrainment”). Here are a few scenes from your cloud day yesterday.
5:45 AM. Gorgeous grouping of Altocumulus castellanus and floccus. They’re coming at you. (If you thinking of soft orchestral music here, you may be remembering well-known orchestra leader, Andre Castellanus.7:37 AM. Here a castellanus turret rises five to six thousand feet above its base. Had never seen one this skinny and THAT tall before. Was really pumped about the mid-level instability at this time. It wouldn’t last. The great height is indicated by the luminosity of the top,Also at 7:37 AM, another amazinging tall turret rises up from quiescent bases, ones not connected to ground currents. The bouoyancy in these clouds is due to the heat released when moist air condenses (latent heat of condensation). When the temperature drops rapidly with increasing height, that bit of heat released is enough to allow weak updrafts to rise great distances, sometimes becoming Cumulonimbus clouds and thunderstorms. These clouds, due to their size, would no longer be considered just Altocumulus andre castellanus, but rather Cumulus congestus. Here’s where our cloud naming system falters some. Later, a couple of these grouping did become small Cumulonimbus clouds with RW- (light rain showers).7:11 AM. The great height of these tops was also indicated by the formation of ice, that faint veil around the edges. Stood outside for a few minutes, thinking I might experience some drops, but didn’t.7:38 AM. The top of this Cumulus congestus has just reached the level where ice will form in the top.10:22 AM. Cumulus congestus clouds began their transitions to Cumulonimbus clouds early and often over and downwind from the Catalinas. Can you spot the glaciating turret in the middle, background? Pretty good skill level if you can.10:23 AM. Here’s a close up of that turret in rapid transition to ice. It was this kind of phenomenon that led Hobbs and Rangno and Rangno and Hobbs to reject the Hallett-Mossop theory of riming-splintering as THE major factor in ice production in Cumulus to Cumulonimbus transitions like these. The high concentrations of ice particles happened faster than could be explained by riming and splintering, or so it was thought. Still think that, but am in the minority, though there have been reports of inexplicable, fast ice development like that Stith et al paper (with Heysmfield!) in 2004 that for a time appeared to put the “icing on the career cake.” Incredible ice concentrations were found in updrafts of tropical Cu for which there was no explanation! That finding hasn’t been replicated by others, casting doubt on the whole damn paper! “Dammitall”, to cuss that bit.11:04 AM. Nice Cumulonimbus capillatus incus (has anvil) pounds up toward Oracle way. Tops are not that high, maybe less than 25 kft.3:41 PM. The air aloft began to warm and an inversion capped most of the convection causing the tops of Cumulus clouds to spread out and create a cloudy mid to late afternoon. Nice, if you’re working outside in mid-May. Since the tops were colder than -10 °C (14 °F) the ice-forming levels, some slight amounts of ice virga and sprinkles came out of these splotches of Stratocumulus clouds. One passed through the Sutherland Heights, but if you weren’t outside you would never have known it!4:38 PM. Isolated rain shafts indicate some top bulges are reached well beyond the ice-forming level. Note grass fire in the distance.7:22 PM. Pretty nice sunset due to multi-level clouds, some Stratocumulus, Altocumulus, and a distant Cumulonimbus anvil.
More troughiness and winds ahead during the next week as has been foretold in our models, and reinforced by weather “spaghetti” plots, after our brief warm up today. No rain here, though. Seems now like rain can only occur at the very end of the month where weaker upper troughs coming out of the Pac appear to be able to reach down and fetch some tropical air.
The End
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1Its gone now because I couldn’t finish yesterday. Went off to Benson for horse training with Zeus.
I was really happy for everyone out there when the skies were dotted with so many perfect examples of Cumulus humilis. It was like a numismatist finding a perfect Indian head penny. If you were like me, and I suspect you are, you were just going CRAZY taking pictures of those flat little pancake clouds. Those clouds were pretty much limited to about 1,000 feet (300 m) thick at most
Not cold enough for ice in them, of course, since the temperatures at Cumulus cloud tops were only around -3 ° to -5 °C (28 ° to 23 ° F, respectively). Around here, ice USUALLY does not appear in clouds until the temperature is lower than -10 °C at cloud top.
Yesterday began with some light snow falling on Mt Lemmon…well, it was falling downward TOWARD Ms Lemmon, actually. Fell out of some thick Altocumulus clouds up there around where the cloud top temperature is… what? OK, silly question for you, probably lower than -15 °C (5 ° F).
Let’s check the sounding to be sure, remembering that the launch site (University of AZ) was downwind of air flowing from the NW yesterday that went over the Catalinas, so a sounding at the U of AZ might suggest higher temperatures than this cloud was actually at since the air was probably descending before it got there.
Indeed, as just seen by me, the TUS sounding indicates that layer, up around 14 kft above sea level, 11 kft or so above Catalina, not a city, but rather a Census Designated Place or CDP, was “only”at -10 ° C.
I reject that as the temperature of the virga-ing cloud over Ms. Lemmon! Its a little too warm IMO.
8:41 AM. That white haze under the Altocumulus clouds is composed of ice crystals, concentrations probably a couple or less per liter of air. Likely stellar or plate crystals, ones that form at temperatures less than -10 ° C. Almost certainly no aggregates of crystals; concentrations too low to form “snowflakes” which are aggregates of single crystals. Snowflakes form when higher concentrations of crystals collide and get locked together, as in stellars, and their cousins, dendrites, that grow in a similar temperature regime. Dendritic crystals are usually seen in deeper clouds than these because those crystals have time to grow extensions in various directions, are not just “planar” ones. If the cloud is thin like this one, not much growth can take place in the droplet cloud and simpler crystals like hexagonal plates and stellars (Christmas card crystals) fall out. There is a lot of hand-waving here….10:20 AM. A horse named “Zeus” looks to see if any Cumulus clouds are forming over the Mogollon Rim to the NE, or, maybe he’s fixated on the horses in that corral below…
By afternoon, the skies over Catalinaland were spotted and dotted with spectacular Cumulis humilis examples. (The littlest shred clouds are Cumulus “fractus.”)
I’ve left the time of the photos off today. After all, there was only one true time yesterday, “perfect humilis time!” or as we like to say, “PHT.” Immerse yourself.
Yesterday was a great day both for airborne researchers studying the onset of ice in clouds, and for my followers to test their “ice” Q detecting abilities, to come up with a clever play on words there.
What was so great about yesterday’s clouds?
Well, they were real cold, bases up around 9,000 feet above Catalina (about 12,500 feet above sea level) at -7° C (19° F). Excellent. Nice data point.
Cloud tops?
This is what was pretty great for you and me; they didn’t overshoot much, the clouds were pretty flat, not very deep, not a lot of flight time needed climbing to cloud top to see what it was around here. That means that if you are flying around up there sampling clouds for ice content, that the tops you smashed with your aircraft were pretty much the ones at the temperature that the ice crystals you ran into later formed at. Remember, when cloud tops first rise up, they usually have little detectable ice (the ice crystals are too small for your instruments, or, they haven’t formed yet, takes a little time.
When there are big overshooting tops, an inexperienced, well, crummy researcher in an aircraft finding the ice, as it is usually found, lower down in the cloud, might put the origin of the ice at the temperature of the collapsed top, not at the lower temperature where it formed and the original top reached up to.
So, the lack of much overshooting made it a great day to assign the ice you found to the right cloud top temperatures.
What else was great?
It was a marginal day for ice formation here in the Catalina area, so you get a good data point on when ice starts to form in clouds given that base temperature. As the cloud deepens upward, more ice would be expected with the lower temperatures.
And, as noted by Ludlum way back in the 1950s, and by Prof. Battan right here at the University of Arizona which I did not attend, btw, that level at which ice and precip onsets changes from day to day (largely related to how warm (crazy isn’t it?) the cloud base temperature is. On days with warmer cloud bases, the ice onset temperature is also higher. For example, in summer here, its not unusual to have ice onset between temperatures of -5° and -10° C (23° and 14° F) when bases are warmer than about 10° C.
Anybody still out there?
So, yesterday, with the deepest Cumulus clouds around 2,000 to three thousand feet thick right in our area (they were deeper elsewhere), tops were running around -15° C, this temperature, as you know, leads to the formation of plate-like crystals, hexagonal plates, stellars (Christmas card crystals), maybe some spatial dendrites (stick out in different directions) if the latter crystals were in the Cumulus cloud long enough. If the concentrations of ice get high enough, you’ll get “snowflakes”, interlocking dendritic crystals. A single, good-sized snowflake might have 20-50 individual dendritic crystals.
Is anybody still out there?
Below some shots from yesterday afternoon when there were traces of ice spewing out of local clouds. Did you see those regions and note them in your cloud diaries, that’s the important question.
3:23 PM. A nice view of the overall scene around here with our small Cumulus clouds (Cumulus humilis and mediocris). You see a house in the distance off this dirt road. Pretty say when you think that in America some people still live on dirt roads.3:49 PM. Oh, there’s a nice little Cumulus toward the Charoleau Gap. Doesn’t seem to have any ice…. Let us look closer, and, of course, we look for ice to appear at the downwind edge where cloudy air has been in the cloud the longest, see if anything is falling out.3:49 PM zoomed view. Oops there it is, a little ice, single crystals, concentrations likely lower than 1 per liter of air. You wouldn’t expect to find any “aggregates” here, since they require higher concentrations of ice to bump into each other and lock together. Wow, this is an incredible amount information based on a little hazy spot in a photograph!4:13 PM. Lets look over here toward the south. OK, there’s an obvious ice haze beyond the Catalinas, but what about the cloud in the middle? See anything coming out the downwind (right) side?4:13 PM zoomed view of the fall of ice crystals out of this cloud. This patch of ice haze is so obvious it would have been pretty embarrassing for you not to have noticed it, made a note about it. Of course, we care so much about ice because that’s where nearly all of our rain here in Arizony comes from, as you know, recalling the work of Wegner, Bergeron, and Findeisen, where it was shown that an ice particle in a water cloud will grow at the expense of the droplets around it. For a time, it was thought that all precip of consequence was due to that process, but not so. Ask Hawaiians. Or powder snow lovers about storms consisting only of little dry ice crystals, no water drops in those clouds.
Stormy weather still ahead as noted here I don’t know how long ago. April looking more and more to be a generous month of rain here in Catalina. But will those showers be too late for May flowers?
