Category Archives: Cumulus clouds

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.

Watching rain come out of the Arizona summer sky

Here is a sequence of photos showing the development of a rainshaft from a prior “doing nothing” cloud base.  For a long time, it appeared that these dark clouds, bottoms of Cumulus clouds, were too raggedy, not contiguous enough in a nice, large and dark region indicating a wide updraft, one  that might push cloud tops to the “glaciation” level where ice forms magically and spreads throughout the cloud top.   Our Cumulus clouds,  at this warm time of the year,  must climb to about 20,000 feet or more above sea level, or to the -10 C (14 F) level,  before the liquid cloud drops in them will freeze to ice, and then only some cloud drops do.   Those first ice particles, surrounded by drops that have not yet frozen,  become hail or “graupel” (aka, “soft hail” you can mash between your fingers) as they collide with those unfrozen drops as they begin to fall out.

So, no rainshaft, no tops to 20,000 feet or more, no matter how dark the clouds may look.   At least for a long time yesterday, they did nothing.  You’re thinking, “What a waste!”  and, “So close!” (to precipitating).  I did, for sure,  as I thought a chance for rain in the area was going to be missed.

But then, there it was (look hard, straight above the tree near the middle of the 2nd photo) !  A thin strand of rain dropping out of those dark bases, a strand that quickly became a downspout, then a huge rainshaft clobbering,  maybe Saddlebrooke!  Very nice, dramatic to see.

Here’s the main sequence of that.  First the line of non-raining cloud bases is shown, and then the cloud base area where the shaft began to fall out.  After that, it lengthened, broadened into a full rainshaft.  Notice the curvature to the left as it went down toward the ground, showing the N wind underneath cloud base.  This is SUCH an exciting time because you’ve been waiting and waiting for something to happen and begin to wonder whether it will at all.

We only got a trace, a few drops.  But the air cooled nicely, followed by another fabulous Arizona sunset producing that little bit of paradise.











Why was there a line of clouds like that shown over Cat land yesterday evening?

Clash of the “outflow” winds from thunderstorms in the area, that were meeting below that line of cloud bases.  That wind clash passed through this location at 6 PM LST when the wind shifted from the southwest to the north.   Above these kinds of clashes, the air is forced to rise and enhanced clouds, or a line of clouds forms. Some areas got over 2 inches yesterday between Colossal Cave and Benson.  Check these amounts out here.

Here’s one of last evening’s sunset, for a little color,  “Arizona gold” in here to break up all the gray:

“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 bottoms1. 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!”

Too much “Altostratus cumulonimbogenitus”

Yes, that really is a cloud name;  kinda silly really.  Oh, well….

First, since there wasn’t enough rain here to make me happy–there wasn’t ANY in Catalina yesterday, I thought I would start out by making people feel better with a “Clouds R Fun” photo from yesterday.  Here are two “puppy” clouds, side by side, ones I thought might grow up to be Great Danes, but didn’t.  Still, they’re awfully cute anyway.  You just want to cuddle them.

Now that we’re all feeling that bit better thinking about puppies, we can move ahead to solving what happened and why Mr. Cloud Person’s expectations of signicant rain in the immediate area were not realized.   If you are a really good sky watcher, off in the distance, large Cumulus and Cumulonimbus erupted explosively well before noon.  I was so happy!  This could be a “totally awesome” day, I thought!   Look at these photos taken  at distance “Cbs” to the south of Catalina before Noon.

In the first shot taken at 11:45 AM, to the right, a full blown “Cb”, to the left partially hidden by Pusch Ridge, Cumulus congestus clouds.  Now look at the next photo in that same direction.   That group of Cumulus congestus beyond Pusch Ridge have exploded into a massive Cb with a giant anvil (“incus”)!  Areas near Green Valley, toward which these photos are taken,  got 1-1.5 inches.

But there was something pernicious going on right in front of my eyes; those huge anvils (“inci?”) that were being ejected by these explosive thunderheads.  Those can actually be a BAD thing because if they spread over the whole sky, they tend to kill off the Cumulus clouds underneath them by shading the ground, often teamed up with a subsiding air pattern.  While the air rushes upward in hot spots in these complexes, there must be compensating downward and cloud killing motions somewhere around it. It seemed to be the case as that huge complex S of us yesterday afternoon fizzled out and left a giant mass of—you’ll want to exercise you tongue before trying to pronounce this—“Altostratus cumulonimbogenitus” spread over the sky in the afternoon (last photo of a Seattle-like sky over Catalina). This smooth layer cloud is really just the remains of thick anvil clouds from all those “Cumulonimbus capillatus incus” clouds earlier in the day to the south of us.

Were there huge storms relatively nearby yesterday?

You bet!  Take a look at this loop from IPS Meteorstar, one that combines radar echoes and shows the spread of the thunderstorm anvils, the “whitest” and coldest topped clouds in this loop.   Notice what happens near the southern Arizona border about the time the second two photos above were taken.  Just an explosion of grouped thunderstorms with their flash floods that we call “meso-scale” complexes.  With luck, a bit different weather pattern, we could have been under that. Darn.  We’re still having conditions to produce large severe storms.  Maybe today will be our day.

Here’s are the cloud signs for today for why it is especially ripe for high rainfalls:  Its moist through about 40,000 feet above the ground and the cloud bases are LOWER today than yesterday.

How could you tell that just gawking at the sky and our Catalina mountains?  Well, you got yer Cirrus (high level moisture), you got yer Altocumulus (mid-level moisture) and you got yer Stratocumulus, some of which are topping Mt. Sara Lemmon (low level moisture)!

Now this last factor is really good in indicating the chances of 1-2 inch rains under the main shafts of our thunderstorms today–nothing too unusual, however, for AZ .  Lower cloud bases means warmer cloud bases, and warmer cloud bases in the summertime is like adding a furnace inside those towering Cumulus clouds due to heat released when condensation occurs.  And the warmer the cloud bases, the more water that is being condensed inside them.  Is anybody still reading this? Better quit here; I’m even getting saturated.


The End.

Stormy, pretty weather

It’s great when things are as they are supposed to be.  Below, “the usual” kinds of scenes in July in southeast AZ from yesterday, such as Cumulus boiling off Mt Lemmon in the late morning, followed by dense rainshafts in almost every direction in the later afternoon.  I love these scenes!

Well, “usual” for SE AZ, except that high reaches of the Canyon del Oro wash watershed were deluged by 2-3 inches of rain (see two of those dumps in progress in the second and third photos below).   And Mt. Sara Lemmon had over 2 inches! (Must check washes out this morning to see if any are running around Catalina and environs, and how green it is already starting to get.

Here in Catalina land, after another 0.27 inches yesterday and overnight, we now have had 2.37 inches since the beginning of July!

The very pleasant news ahead is that the numerical forecast model by our friends in Canada, that can be seen here, is now suggesting, based on last evening’s data, that a series of itty bitty disturbances1 in the upper air are going to affect our region from now through July 13th.  These little lows/troughs arise from the tropics and their role is to take the underlying humid air and organize it into larger clusters of thunderheads (aka, “Cumulonimbus capillatus incus” clouds;  use this name if you want to impress your friends) so that the rains last longer, and might be heavier than on days with no disturbances aloft.  How cool is this forecast except for those times when the roads are impassable?

I have not yet checked other model outputs, ones that might be different, because I like this Canadian one the best already and don’t want to know other things that might ruin my current very good mood.  Ignorance truly IS bliss!  However, I do feel that the “pendulum” has swung back to the wet side here, as it always eventually does in climate, and so there is that pinch of intuition thrown in that wet forecasts are more likely to be correct.  Lets hope so.

Finally, even ordinary gray skies are pretty, even dramatic and interesting in weather like this.  Check out the last photo, taken in the evening after the first rains in Catalina.

The End.

1 In the perhaps unneeded technical jargon of atmospheric sciences, they might be described as “mesoscale”–namely, ones much smaller than the gigantic highs and lows we see on the usual weather maps for the whole US











0.73 inches

Bullseye thunderstorm off the Catalina’s between 12:30  and 1:30 PM really did it, dropping a miraculous 0.55 inches.  I suspect that 300 yards N and S got less than our driveway did where the gage is located.   The smells, the puddles, the water running down the road; it was all so marvelous, and seemingly it has been decades since we saw this kind of sight.  And then, after it looked like it might be “all over”. that dramatic darkening of the lower cloud bases pushing over the Catalinas from the east suddenly began to occur around 6 PM, followed by another nice rain of 0.14 inches.   While we did not get the core of that massive system, it was great to see all the rain fall in western Tucson from here, knowing how dry it is everywhere.   Finally, that little bit of rain after dark, plumped the gage another 0.04 inches to bring the total to a wondrous 0.73 inches, every drop so necessary now!

Below, a sequence of the cumulus building off the Catalinas, beginning around 10 AM, ending with the approach of the main “dump” just after 1 PM.  Sometimes seeing this happen, and being so close to it reminds me of being in an airplane meandering among the Cumulus.  The second shot is a great indicator for the rest of the day, a tall, skinny little cloud1 that shows just how ready the atmosphere is to allow huge clouds like yesterday to happen.  Seeing that type of cloud should really get you excited about what the rest of the day holds.

An even better way to view yesterday, in a cross section mode, is from the U of AZ time lapse video here.  You’ll be amazed by these “volcanic eruptions” of Cumulus and Cumulonimbus clouds over Mt. Sara Lemmon.  Better hurry though.  Movie is overwritten by today’s later on!


Finally, the “icing on the cake” to be quite unoriginal; that wonderful sunset.

The End except for the footnote.

1You might well call the cloud in the second shot,  “Cumulus castellanus”, though technically there is no “castellanus” variety for Cumulus as there is for other cloud genera like Stratocumulus.  You could just call it a “towering cumulus”, the kind of remarks seen in airport aviation weather reports, though for some reason my mind always drifts into other domains completely;  paleontology, anthropology, and I think of that early man, Homo erectus.  Perhaps it was too risqué for those naming clouds to use that modifier as a variety name.

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.

First thunder

While only a disappointing trace of rain was observed here, it was so stimulating to see that evening lightning flicker beyond the Catalina mountains for the first time this summer.  And then see more lightning, unexpectedly, close enough to produce the first thunder early this morning between 2-4 AM.   A few large, sparse drops fell for about 8 seconds I think.  Here is are the local rain reports for the past 24 h for our region.  Almost an inch fell in parts of “Greater Tucson”!  How nice!

But perhaps the nicest part of yesterday was that little cloud that sprung up toward sunset to the south over Pusch Ridge.  Here is a sequence of shots from that pretty, narrow little thing that climbed high enough to reach the “glaciation level”–where the cloud top converts to ice, and voila, a little precip falls out.  These were taken at about 5 min intervals.    The first shot would be a cloud classified as a Cumulus congestus, the second might be Cumulonimbus calvus (“bald”), the crenelated top in the first shot is disappearing as ice takes over from the former mostly droplet composition,  and the last, Cumulonimbus capillatus (with “hair”).   Note:  Bald grew hair!  This is a common sequence for larger Cumulus clouds.  The frizzy top in the last photo is completely comprised of ice.  What made this so nice was how isolated and “photogenic” the cloud was.   It fizzled out a little later, and I thought we were doomed for a dry overnight.  The weather here can always surprise you!

“Pyrocumulus”, an awful sight yesterday evening

There may have been some sharp eyed folks that saw a great looking Cumulus congestus in the distance off to the NNE of Catalina yesterday.   The shots below were just before 7 PM LST.  Perhaps there was a shower or thunderstorm on the Mogollon Rim.

Sadly, even I was fooled for a few microseconds until you notice that there is NOTHING even slightly resembling the size of that cloud anywhere in the sky.  Then,  it dawns on you that it must be a “pyrocumulus”, the kinds of artificial Cumulus clouds that form atop the highest, and hottest portions of fires when there is a bit of humidity in the air. Once the fire dies down some, then all you see is smoke, the last evidence of the trees and the plant life consumed below.  Likely was a new fire, too, dammitall.    It was probably 50-75 miles away;  also just visible in the satellite imagery.   The second shot is an attempt at a close up, marred a bit by some kind of large insect that happened to fly by as I was shooting.  Just above the horizon of that second photo, you can JUST make out the telltale smoke below the bottom of the pyrocu.  The last photo, from Hornepayne, Ontario, Canada, is an example of a pyrocu up close, just as it was forming.  This was due to a prescribed burn by the Canadian government.  The cloud droplets are white while the smoke is black.   The cloud droplets are about 100 to 1000 times larger than the smoke particles, and reflect (have a higher albedo) more of the sun’s light than do the smoke particles.


Rain update:  Still looks like a great onset of the rainy season after a little “hip fake” today and tomorrow, that is,  a slight insertion of tropical air ahead of an unusually strong, winter-like storm in northern California.  That weak insertion of tropical air should lead to a few weak, high-based showers and thunderstorms on the high terrain.  And with high bases, there will be the chance of exceptional winds near showers due to the virga and rain falling into otherwise pretty dry air.   After this little episode,  the normal summertime anticyclone aloft rears up from the Tropics and after a couple of dry days and plants itself to the north of us.  This allows more humid tropical air to arrive pretty much on time, around the 3rd and 4th of July.  So, get ready!  It will be so great to see all the dust washed off the cacti, the stupendous sunsets, the lightning, the rainshafts, the whole works.  I’ve waited a year for this season to roll around again!  There won’t be a living thing that is not “happy” by the middle of July I would think, unless there has been too much flooding, always a possibility here.


First hot air Cumulus over the Cat Mountains, Friday, June 17th

Small now, but what portent for the summer weeks ahead when it’s big brothers will show up over the Catalina Mountains;  a real milestone, so pretty.  This photo was yesterday, at 2:45 PM, when it was 101 F!  Cloud name: Cumulus humilis or Cumulus fractus.

Later, smoky Altocumulus filled in before and at sunset as a wisp of tropical air also drifted into Arizona.  Unfortunately, that was it for our hint of the summer rain season as this morning there were no clouds in sight.

If you look carefully at the orangish sky around the Altocumulus, you can see something that looks like very faint cloud ghosts, patches of whiter sky.   Those are moist areas at the same level as the Altocumulus where the air is nearing saturation, and some of the aerosol (smog) particles have fattened up as they “deliquesce”, absorb some water vapor, and when they get larger as a result, scatter more of the sun’s light.  That produces a faint ghost of a cloud that may be ready to appear if the air gets more moist.  Typically the relative humidity is 60-80 percent when particles begin “deliquescing.”    Some of our greatest summer days are humid, with low cloud bases on the Catalinas, and yet there is no evidence of haze whatsoever.  That means the air must REALLY be clean!

There was a suggestion of virga in clouds downwind of the Catalinas at sunset, but it was marginal if even there.  So, what was the temperature of those Altocumulus?  Those clouds could still be below freezing, but a good guess would be warmer than -10 C (14 F).  The TUS sounding indicated that they were at -12.5 C, marginal for ice crystals to form (and precipitation to fall out).