Altocumulus clouds – Page 25

In case you missed it-a spectacular, if odd, partial rainbow

Have never seen anything like this, shot taken about 5:50 AM LST yesterday, July 26th. My best guess is that it was a partial rainbow, made possible by the small region of rain falling out of these Altocumulus opacus clouds. Probably some bulges in those tops above where the rain is falling so that they reached the “glaciation” level, but then the precip as snow, melts into rain just below cloud base. The low sun angle produces what would be the most gigantic rainbow ever, running about from due S to due N if complete. Is that even possible? The lower the sun angle, the dimmer the light, the larger is the arc of the rainbow. Will have to research this some more.

Some further thoughts… When you see VERY localized occurrences of precip from widespread cloud sheets like this, the possibility arises that it could have been created by the passage of an aircraft. An aircraft, under certain special conditions, CAN create precipitation in supercooled clouds–there was global publicity on this phenomenon recently asserting that airports could be affected by aircraft in snow situations. A friend was flying to New Hampshire yesterday out of TUS, and I wonder if her plane left this salutation? Hahahah, sort of. Most often, a hole in the layer is observed when that happens, and so the thought that it WAS an aircraft is somewhat suspect.

Go here, if you want to really get deep in this aircraft phenomenon. (Yes, Mr. Cloud-maven himself was involved in the reporting of this phenomenomanonanon)

The End

Less color, more filling…

of raingauges wanted. It was another spectacular sunset yesterday evening after another dry day here in Catalina. You hate to see a completely dry day go by during our peak of the summer rain season, July 5th through August 20th.

Below, the best we could do over Mt. Sara Lemmon in the way of Cumulus clouds, a “medicocris” one is what I would call it, followed by a couple of shots of that great sunset. That Cumulus was pretty pathetic I thought, though it was trying as hard as it could. You really don’t want to be a Cumulus mediocris in life, but there it is, and that’s as “important” as that cloud got, to the “mediocris” stage. Really hoped for more yesterday, too, since the morning Altocumulus cloud bases were a bit lower than the prior dry day. Some remnants of the morning Altocumulus are there above that Cu med.

If you caught the remnant of the moon yesterday morning through those Altocumulus clouds, you saw something a bit unusual. You couldn’t detect any cloud movement. In fact, the relative movement of the moon toward moonset almost seemed faster than the cloud movement! That’s not good for storms either, since its better if there is a bit of wind shear, turning and speed increases with height, not virtually calm all the way up. If you want to read a little more deeply about this sort of thing from one of the world’s best experts on convection, Bob Maddox, who lives right here in Tucson, go here to Maddweather. Has a great web page on our weather, and storm structures.

Learned something, too, yesterday. I did not think you could have Altocumulus lenticular (sliver) clouds with virtually 2 kts of wind. But, there they were in these sunset photos. An old weather saw, obviously a bit flawed, is that lenticular clouds require appreciable wind.

The models are wetting it up here over the next few days, and we’re not that far from conditions that produce large storms. In this last photo. taken at 7:02 PM, you can make out a Cumulonimbus cloud on the SW horizon, and the huge gray shield to the S was the remnant of a large cluster of storms near the border. So, get ready, and dust your gauges off!

The End.

Last, after The End, is the NWS sounding (courtesy of the U of AZ Dept Atmos. Sci.) for yesterday around 5 PM LST. Where the green line pinches in toward the white line is where the two cloud layers shown in the sunset photo were located. On the far right are the wind “barbs” showing how light the wind was, less than 7 kts.

Thursday, July 21: a dry day with a nice sunset

Here’s the sunset, in case you missed it and were watching something like Entertainment Tonight and weren’t out enjoying the real world, which is so much better:

Now for some educational material. And don’t tell me, “We don’t need no education”–who were the morons who sang that??? (Of course, you all know the answer, Led Zeppelin). Whoever they were, they didn’t exactly change the world via new knowledge, did they? Still, it wasn’t a bad tune. I kind of liked it.

OK, back to clouds after that musical interlude. You don’t see any “virga” from these Altocumulus clouds (I know I did NOT have to tell you they were Altocumulus clouds, either, did I? You already knew that by now, so forgive me).

But, you see no fall out of snow, yes that’s right, up there (in this case, about 17,000 feet above us) it would be snow dropping out of these clouds if there was some fallout from them. Here’s the quiz: What is the cloud top temperature of these clouds? No help from the audience, please.

“Warmer than -10 C (14 F), and maybe even -15 C (5 F)?” Congratulations. You have won a trip to this web site; you will not be banned as some kind of cloud miscreant.

Yes, its true. Even though clouds can be well below freezing, nature makes it hard to produce ice at times. Typically, in mid-level clouds like these, the fall of snow out of them does not occur until they are at least as cold as -10 C (14 F), and every so often they can be as cold as -30 C (-22 F) with no ice. Ice formation remains a bit of an enigma in our field.

On the other hand, clouds with warm bases, like the ones we have here on our most moist days (when they are about 10 C (50 F), can form ice between -5 and -10 C. Its all about the sizes of the drops that accompany the cloud as it rises up into the freezing level; the bigger they are the higher is the temperature at which ice forms. And with warmer cloud bases, the drops are bigger when they arrive at the freezing level in the tops of Cumulus clouds.

The End.

“Groundhog Day” all over again

If you mainly focus on going to movies about weathermen, you will remember this classic along with Steve Martin’s “LA Story.” Bill Murray, the weatherman, is condemned to live the same day over and over again until he gets it right. Since yesterday was a near repeat in many respects to the failed rain day of Monday, this seemed like an appropriate title.

1. OK, morning: some really nice Altocumulus castellanus (miniature Cumulus clouds with flat bottoms) and “floccus”–raggedy bottoms^1.These indicate a nice drop in temperature as you go upward in the “middle-levels” (around 10-15 Kft above the ground) and that in turn helps the formation of thunderstorms.

2. Clouds topping Mt. Sara Lemmon again indicating a grade of “juicy” moisture hereabouts.

3. Very early thunderstorm, first thunder heard a 10:40 AM in a mountainous Cb N of the Cat Mountains (shown below in its, “Cumulonimbus calvus” stage; top is ice, but is not yet CLEARLY fibrous, striated).

Seemingly all is in place for large thunderstorms to be scattered hither and thither later in the day, rumbling and banging around, scaring cats and dogs with lightning sabres, blinding rain, puddles in the road, TEEVEES out of whack, missing your favorite show, “TV party tonight²” canceled. OK, enough dramatics and songs².

But it didn’t happen did it? Why not?

One of those very circulations foretold in the numerical models slipped over us yesterday during the day, and as these circulations do (you can see it here in this long “water vapor” loop)-you’ll need a broadband connection to see this. You’ll see a miniature low spin into SE AZ from Sonora, MX, late on the 11th-early yesterday morning. The darker area rearward of this circulation represents horrible drier air in the mid-levels especially. The whole point of this loop is to show that drier air moved in and desiccated the otherwise growing Cumulus clouds following the passage of this micro low above us. The very raggedy tops of our afternoon Cumulus clouds was an indicator of this extremely dry air that did not allow them to explode upward with the afternoon’s heating.

You could see this happening since, in a homogeneous air mass, there would be no full blown Cumulonimbus clouds just to the north semi-circle of Catalina, and only weak Cumulus with ragged tops spearing that dry air at the same time in the southern semi-circle from Catalina. I started to get depressed. Something was going wrong, the air was getting too dry upwind.

Still, the there were enough Cumulus and Stratocumulus around at sunset to produce another memorable sunset. Maybe that’s reward enough.

The End.

¹distinguishing between the two is a bit silly IMO.

²Who can forget the Black Flag tune, “TV Party Tonight”? “We’re gonna have a TV party tonight! All right!”

Invasion of the water molecules

At least more of them…. Overnight (take a look here), the dewpoint temperature, a measure of how much frost would build up in your refrigerator freezer and/or drip down the walls of it if you left the doors open and the refrigerator on, climbed a whopping ten degrees early this morning!

Yay, “mo better” humidity for storms! This will mean lower cloud bases today, and that in turn means that the rain that falls out of the thunderheads with their anvils (aka, “Cumulonimbus capillatus incus” clouds, if you want to impress your friends) will reach the ground in torrents; the rainshafts will be opaque under those clouds. This will be quite unlike yesterday, where rain fell, grudgingly it seemed, from the isolated, high-based, and rather shallow Cumulonimbus clouds seen around Catalina. This is the first day that, to focus on MYSELF for a second, I….have waited for all year! I am not one of those little babies that can’t take a little heat and humidity of the Arizona summer and have to head off to his/her mountain palaces or shacks, as the case may be.

Now, of course, if you have any photographic documentation inclinations, you’ll definitely want to get some “before” shots of dusty cacti, dust-covered mesquite trees, your car, check the amount rocks around the little hill your house is on (I don’t think we have enough, for example) and be ready to get some “after” shots once our summer summer’s rains begin and the dead desert springs to life, one of nature’s big miracles around here. In fact, it would be that bit better if you had a time lapse camera set up so that we could see this change take place over a period of a month or two. Thanks in advance for doing this! I look forward to seeing your work.

Below, an example of dead desert taken during a horseback ride yesterday. Also note in the second photo, some large black birds in formation on the top of telephone poles, wings out. Sometimes they extend for miles on top of telephone poles. They do this when the relative humidity is about to go up in some kind of homage. (OK, I made this up.)

How much rain can fall in our most intense rainshafts, the kind that you can’t see through, are virtually black, and also have just dropped down from the cloud? (In “conversational meteorology”, when this happens, you might exclaim to dinner guests, “What happened to the view of the Tortolitas? Just a minute ago there was only a dark cloud base over them, and now, 2 minutes later you can’t see them at all! Man, look at that shaft of rain over there!” A murmur develops among your guests… They’re impressed by your interest in natural events.

Well, we have our measurements here in Arizona. And once in a great while, something extraordinary like this “bottom drops out” situation hits a hi res gage. Well, Floridians, you don’t have that much on us. Our gages have indicated that a whopping 1-2 inches of rain can fall in but 15 minutes! Unbelievable! In those cases, its pretty much a whiteout inside the heart of that newly fallen shaft, and your roof will become the equivalent of Bridal Veil Falls, Yosemite.

Please note black dots on top of telephone poles in second photo. They’re birds. A close up follows, so that you can see I did not just make this up. The clouds? Center: Altocumulus opacus virgae (has some stuff falling out it) with some “perlucidus” thrown in.

The End, except for the photos below.

Sunrise and sunset heaven: Cirrus and maybe Altocumulus on the way

Yep, a cute tiny little upper air low with just a dollop of high clouds is going to be spit out of the eastern Pacific off Baja Cal today and tomorrow and toward AZ, and along with that will come some Cirrus and probably Altocumulus floccus and castellanus clouds, maybe with virga. The first Cirrus cloud is likely to get here by late afternoon or evening today, and the sky should be full of high, icy Cirrus clouds tomorrow morning. So charge your camera batteries now for some of the “everyday-but stupendous” AZ color at sunset today and at sunrise tomorrow. You’ve been warned.

Below a map of the air flow and pressure patterns at 300 mb, or about 30,000 feet, the domain where cirriform clouds like to reside, valid at 5 AM LST this morning.

“Oh so pretty….”

You know the rest of the words to this song, the punch line, “…pretty ugly.” Yes, who can forget Johnny Rotten….?

Gorgeous clouds yesterday, but no rain is going to follow them (the “ugly” part)! I had really hoped for a splotch of glaciating Stratocumulus clouds this morning after the great display of….the tongue twister, Altocumulus (Ac) perlucidus undulatus, a mid-level cloud with a honey-comb of elements (“perlucidus”), and those elements also aligned in rows (“undulatus”). If you looked off toward Twin Peaks, you saw that the the back edge to these clouds was very smooth looking and did not advance toward us. That was an Ac lenticularis cloud that started the whole shebang. That lenticular cloud, as often happens, devolved into little cloudlets and rows; its smooth lenticular form devolving into cloudlets that trailed downwind over us here in Catalina. See pretty pictures below. One has the crescent moon in it.

Now it looks “pretty ugly” here for rain since there are no clouds this AM! “Dang”, as a friend would say.

Why get excited about the chance of a sprinkle, or at least some pretty virga this morning because of the two layers of clouds yesterday afternoon? No model indicated any rain. First, it doesn’t happen often, but to HELL with models, they can be WRONG. Don’t bet against them too often, though. You will lose everything.

So, if you were just eye-balling the movement of those two cloud layers later yesterday afternoon and using the crescent moon as your fix, you saw that those mid-level Ac clouds were jetting along at a tremendous speed as they passed it.

How fast?

The NWS balloon sounding indicated that at the height of those pretty Ac clouds, about 20,000 feet above ground level, they were blowing along at no less than 80-90 mph (70-75 knots)! This is a really strong jet for May! And it indicated that the jet stream must be right over us, or darn close, and it was blowing from the SW. If you no doubt know, Buys-Ballots Law, in the northern hemisphere means that a low or trough is to the west of you, and in this case; above you, not at ground level since you’re looking at higher clouds.

Also, the small Cumulus were beginning to cluster into Stratocumulus over the Catalina Mountains. Getting pumped because there movement was showing more southerly now; the wind was more southerly at that level than it had been in the morning, also suggesting the influence of the trough to the west. Here they are. If you really want to relive yesterday’s clouds, particular in the afternoon and evening, our friends at the U of Arizona Wildcat Department of Atmospheric Meteorology have captured them

here. For the really sharpies who DO go here, you’ll see that these cloudlets were further devolving in this time lapse to “ghosts” of their former droplet selves in the form of barely visible, icy little veils as they exit the area. So, can you guess the temperature of those clouds? Piece a cake: probably -20 C or less (-4 F or less). Sounding indicates -20 C, BTW.

Perhaps, I mused yesterday afternoon in a bout of wishful thinking, that in the core of that trough heading for us, there’ll be a smidgeon of Pacific moisture left within its interior, enough for some thicker lower clouds than now, and those clouds will be cold enough, too, so that they will form ice inside them and we’ll see some virga (trails of snow fall out of them) or get a sprinkle (in spite of what the models were saying)! Many of you will remember that according to Willis and Rangno (1971–Final Report to the Bureau of Reclamation by EG&G, Inc) that rain can only fall in the wintertime here when you are in the interior of a trough. I’m sure many of you have this report, and can look it up jf you don’t remember.

Well, we should still see a few isolated Cumulus around, small ones, maybe as big as “mediocris” stage (1 km thick or so, 3300 feet). And, with the coldest air over us this afternoon and evening, I am going to stick with an expectation of some ice in those clouds! And you will here about it tomorrow if there is one crystal up there!

Finally, for cloud technicians, how cold will it have to get at cloud top to have ice in those small clouds around here in Arizona today? Well, between about -10 and -15 C (14 to 5 F)–this is somewhat higher than for those mid-level clouds. So we will check that out tomorrow, too!

“The end”, unless I think of something else later.

Footnote: It now appears that last night’s model run of the “Beowulf Cluster” at the U of A has some precip on the Catalinas, between 3-4 PM LST today. Interesting that after I had this thought based on a crude conceptual model, that the “Cluster” would now have that thought as well…. Hmmmm.

Yet another nice sunset

This shot, yesterday just after 7 PM. Light snow (virga) is falling from relatively thick Altocumulus (opacus) clouds. Just above the horizon you can see some little turrets poking up from a row of cloud bases making those clouds Altocumulus castellanus.

Bases of these clouds, according to the balloon data obtained from Tucson Int AP indicated that the bases of these clouds were at about 13,000 feet above us here in Catalina, and the temperature was about 15 degrees F (about -10 C). The tops of the clouds were about 18,000 feet above us, or at a chilly -5 F (-20 C), hence the thin, red-orange curtains of light snow illuminated by the setting sun below these clouds.

The clearing on the horizon marked the last of this “mid-level” moisture that streamed over us here in Catalina yesterday as an upper level bend in the winds, called a “trough” was passing by.

Below is a weather map of the winds (blowing along the green lines) at around 30,000 feet (300 “millibars” of pressure) and the clouds as shown on the satellite imagery. If you look closely where the TUS data is, you can see a little fluff of cloud that made our sunset. A loop of the whole sequence can be found here from our friends at the University of Washington Huskies’ Department of Atmospheric Sciences.

Speaking of the Huskies, here’s what it was like today in Seattle, my former home.

The end.

“Pretty in Pink”

Well, “tending” toward pink, anyway… But who remembers the Psychedelic Furs and what their song title alluded anyway? Of course, no one. But I liked its dark sound. Oh, well.

But here it is, that “pretty in pink” sky (2 shots) from yesterday evening in case you missed it. Again these are Cirrus and Altostratus ice clouds with an isolated exception of Altocumulus lenticularis (just above horizon in the second shot), which is composed of droplets. The second photo is a zoomed shot of the stack (several pancakes on top of one another) of a lenticular cloud off to the NW of Catalina.

Those lenticular clouds should always bring some excitement that things are changing, maybe heading toward a rain situation. Rain did fall in the northern third of AZ when these Ac len clouds were present yesterday evening.

Why the excitement?

While these clouds don’t rain themselves, they are usually precursors of rain situations in the region because they illustrate that the winds aloft are relatively strong, the air in the “mid-levels” (roughly 10 to 20 thousand feet above the ground) has some moisture, and they indicate the kind of “stable” conditions in the mid-levels in their flatness, “pancaked-ness”, that precedes fronts. Of course, we also had those moderate SW winds yesterday that also indicates that “something is going on”.

And something was going on as a cold front traversed the Great Basin yesterday. Even this morning there is still precip in NW New Mexico as of 6:30 AM LST this morning.

And how do we know a new air mass came by?

The temperature change over the last 24 hours, from yesterday at this time to today at this time is one of the best ways of keeping track of fronts and changes in air masses. Here is a plot of that 24 h change. As you can see, the drop in temperature, while it has occurred at my gravel driveway (-5 F) is not quite here in Catalina (though it really is) according to the venerable The Weather Channel’s data which does not have my data (or pressure trace which has the usual sharp rise following a cold front–that heavier, denser, cold air is pushing down on all of us this morning and on my aneroid (not a body part, but a name for a barometer, BTW.)

The last shot here is what the clouds looked like before sunset. Lots of gray indicating they are quite thick and fall into the Altostratus category even though they are very high. Cirrus, by definition, cannot have this much grayness. But, when you see this kind of late afternoon sky, you can almost always count on a great evening scene, that sky especially “pretty in pink.”

Don’t see too many misspelled words, bad sentence structure and other grammatical lapses so will post this now…

In case you missed it…yesterday morning’s sunrise

A belated post, to be sure

Yesterday morning’s sounding when the Altocumulus clouds were overhead. Bases about -18 C, tops -27 C. Lots of ice visible along with widespread virga. Whenever you see this much ice in small Altocumulus clouds like these, you should automatically assume that the temperature at the top is less than -20 C.

Usefulness of this information in everyday conversation, a module I call, “Conversational Meteorology.”

The scene: you’re walking/hiking with a friend on a warm morning when sunrise occurs. You see these clouds. The conversation has died off since you’ve been walking for several hours. You’re looking for something to say to re-energize the conversation. Suddenly, you look up and see this scene below and blurt out, “Man, those clouds are cold!” The volume of your blurtation has surprised even you, and startles your friend who was thinking about that tortoise on the trail ahead of you. You rattle on about how cold the clouds with a followup, “Man, they must be at least colder than -20 C!” Your friend seems puzzled at your excitement, but listens politely’ after all he is your friend. You quickly add, “Almost every cloud has some snow coming out of it, no matter how small it is! Wow!” Your friend, now saturated with your exuberances, asks if you saw the last episode of NCIS last night?

The end.