Category Archives: Cumulus clouds

“Smoke gets in your skies”

Remember that great Harold Arlyn song about smog?  He was pretty upset when he wrote it I would imagine.  Btw, the song was covered later in the 1950s by a group called The Platters…

Below we have a shot of some late afternoon pretty, undulating Cirrus or Cirrostratus… (NOT!)

That was a trick question, actually it wasn’t a question, but it was meant to trick you before you saw the exclamatory statement,  “not!”  Perhaps, I was thinking,  you would seriously consider that this WAS a photo of cirrus for just that instant…but then you would be wrong!

But below, for those with the Calibrated Eye, found only in the most discerning of sky watching folk, you will IMMEDIATELY recognize that those waves, undulations in the sky above the tiny Cumulus fractus cloud at the right, is a smoke layer.  Most likely 15,000 to 20,000  feet above the ground, that is, its also well below the normal Cirrus cloud level.  This is, at present an “eyeball” estimate by yours truly.   How can I find out the actual height?  Maybe in the TUS rawinsonde balloon data.   Smoke layers like this are often made visible by a moist layer because the smoke particles fatten up a bit and are made visible because they have gotten that bit larger and scatter more sunlight.  So, this shot was taken near the time of the balloon ascent, and so I will now look and see if there was a bit of humidity around 20,000 feet above Sea Level (balloon data are reported in heights above sea level,  not above ground level.)  Farther below is the Tucson sounding from our friends at the University of Wyoming, which I had not yet looked at whilst (British spelling) writing the above.

As you can see, while there is a “pinching in” of the temperature and dewpoint traces representing the height of the Cumulus fractus moist layer, there really is nothing but a slight moistening (where the lines pinch in a bit) above that lower moist layer.  So, it would appear that my hypothesis of a moisture layer enhancing the smoke layer should be rejected.  But, as a scientist, I don’t care that I am wrong, because it is WRONG to care about whether you are WRONG as a scientist because we are detached from our hypotheses and only seek truth.  Hon, could you get me a new pen since I just smashed this point on this one?  Thanks.

BTW, if you were on a flight descending through this smoke layer, it would have appeared as though an ugly, thin black line of haze, because, after all, smoke is mostly hydrocarbons which are dark chains of molecules.

So why is it white here, when the sun is behind it?  This is due to “forward scattering” of the wavelengths of sunlight, interfered with by those molecules of smoke, which are, in a sense dispersed.  If you had looked to the opposite direction, to the east, you would not even have seen this layer.  The tiny droplets in the Cumulus fractus cloud are really scattering the light around its edges where droplets are likely smaller than 10 microns in size, though at that size,  about ten to a hundred times larger than the smoke particles.

The waves in the smoke illustrate the virtually ominipresence of  waves in the atmosphere.  We just don’t see them unless there is a smoke or cloud layer.

The End.

Not really, since I will, a bit later, see if I can post a trajectory that will show where this layer came from.


Sometime later…..

The last figure shows air trajectories for 72 hours at three different levels above ground level and each of the end points are at Tucson AP.  Its clear from these trajectories that this “long range” transport haze layer shown in the first photo came out of the Pacific;  it was not a part of any regional fires.  Haze layers like this have often been observed to come all the way across the Pacific or even from Alaksa in the spring and early summer because the storms in the Pacific are weaker, and can’t wash the smog out.  With the jet stream  still very strong at levels of 10-30 kft across the Pacific at this time of year,  these layers can then make it across pretty much intact.

The Twelve…rain drops in Catalina, that is

Well, maybe there were about 27, but anyway….not very many; still,  those drops were to be treasured after not seeing a single  “hydrometeor” display in SE AZ in so–ooooo LONG A TIME!


PG-13 advisory; DRIZZLE is discussed

I have to warn you at this point.  That rain event yesterday WAS NOT DRIZZLE!!!!!!!!!!!!!!!!!!!!!!!!!!!  I will be ROYALLY PO-ed if I hear someone in my social network or a TEEVEE weather presenter say that it “drizzled” yesterday!

Why make a BIG THING out of the correct type of precipitation?

I have to tell you a true story (well, I don’t have to, but I am going to anyway) about the importance of drizzle (i. e., fine, close together drops that appear to FLOAT in the air).   This event happened during my cloud seeding “vigilante” adventures (see Publications for samples).   A well-known professor of cloud seeding in a foreign country asked me to leave his office and never come back after I told him it had been “drizzling” outside, “10s per liter” in the air.

Drizzle is a profound indicator of cloud structure overhead, and the presence of drizzle falling from the clouds in that professor’s region’s meant his numerous reports of how clouds were, ripe for cloud seeding,  were in substantial error.   So you can understand why a report of true “drizzle” would naturally be upsetting to that professor.  Man, am I digressing here!  Yikes.  My apologies. (BTW, those reports WERE in error, confirmed by aircraft years later!   (Spiking football now, with a proper amount of decorum, of course!)


OK, back on task….

With the sky full of low (“boundary layer”) clouds by mid-day (f you’ve forgotten, that was yesterday, May 10th, 2011) and with RW— in the air  (“triple minus”, extremely light rain showers) by 1:30 PM,  with gusty winds,  temperatures in the mid-60s, it turned out to be quite a “storm.”  It just as well could have been but a mostly sunny day with just a scattered Cumulus clouds here and there the way some models were “telling it.”

Here’s a pictorial on how it went, from a Catalina, AZ, perspective:

1) 09:29 AM, itty bitty Cumulus (Cumulus “fractus”) starting to appear,

2) 12:03 PM, larger Cumulus growing up into Cumulus “mediocris” beyond Tortolita Mountains on the horizon,

3) 12:29 PM, virga and rain visible to the NW horizon!  Now I am getting apoplectic since the best models in the world did not have this precipitation over thataway!   But there it is, bigger than watermelons.  The models have to be really red-faced about this! Not everything in the world is predetermined by numerical models; you can  say things that might be right and those models are WRONG!  Just like in the 1970s when a lot people thought global cooling was underway and that’s where we were headed!  But they were WRONG!  Who were those clowns anyway?! (hahaha, sort of).

4) 1:25 PM.  Now where was I before all that excitement?  Oh, yeah.  Here’s some ice for you.  See the frizzy top parts of this cloud in the center of this photo above the dead tree that the birds like to sit in?  Well, them’s ice crystals, and likely snowflakes that have formed in that medium-sized Cumulus cloud (above the dead tree) and its in the upwind direction.  Behind that is more ice and precip falling from a wide area of a Cumulus-Stratocumulus complex.



Quiz.  How cold does the top of THAT cloud have to be to look like that (have that much ice in it, probably a few per liter to maybe 10 or so, not a tremendous amount but significant)?  Well, with bases as cold as they were, near freezing by this time of day at around 7, 000 feet above the ground or 10, 000 feet above sea level, around -15 C (or about 5 F).  Amaze your friends with cloud trivia like this!  Well, maybe not.


5)  1:25 PM.  Here it is, a band of precipitating clouds overhead.  Now the ONLY question remaining, as you gaze upwind at Twin Peaks clearly visible through the precip and virga is, how much will there be?  None? Or as much as a “trace”?   Measurable is out of the question,  looking at this scene below the clouds.  Most of the visibility degradation is due to dusty air, not precip.  Darn.   (Amaze your friends with skills like this!  Well, maybe not.)

6) 3:03 PM.   The End is Near

7) 7:06 PM.  Nice sunset with traces of Cirrus and Ac len on the horizon, driblets from a storm striking the Pac NW.  Isn’t there always a storm striking the Pac NW? I digress again.

Man, I could go on about the weather maps of yesterday, but will quit here.

The end.






















































If you REALLY want to see how it went, take a look at the U of A time lapse video here.

“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.

Exit right (or to the east)

Here’s what happened on top of us yesterday, that gorgeous snow day with so many wonderful sights to see. These maps below,  courtesy of San Francisco State University , for 500 millibar pressure level, about 18,000 feet above sea level, for 5 AM LST as the snow band moved through Catalina, and then 5PM LST,  a little before sunset:



A visual on what the clouds did as this happened yesterday is below. Interpretative cloud statements on the following gallery: shallow, deeper (precip begins in distance), deepest (small, soft hail falls here and there from miniature cumulonimbus clouds), less deep (barely-able-to-precip stage again), shallow, nil. Pics 1,2, 3, 4, 5, and 6, respectively.  If you want all the visual glory of yesterday, go to the U of A time lapse movie here.  However, you’d better hurry, these wonderful films are overwritten each day.  You can really see the clouds flatten out after about 3 PM LST here, and there are some spectacular snow showers going by on the Catalinas.

The end.

























Virga anyone?

Mr. Cloudmaven person foretold certain cloud types would occur yesterday in conjunction with “storm” 3 yesterday (which was really only the passage of an upper level trough over us–see map for 5PM yesterday).  Let’s see how he did, that is, whether he is an actual “cloudmaven”:

(0=not observed, 1 observed, -1, cloud observed, not predicted:

Cirrocumulus,  0

Altocumulus floccus virgae,  0

Cirrus,  1

Cumulus fractus, -1

Cumulus humilis, -1

Cumulus mediocris, -1

Stratocumulus, -1

Stratocumulus virgae, -1

Cloud score:  -4  =s bad cloudmaven; credentials suspect.

Here are some of the cloud sights from yesterday in case you miseed them and want to fill in some entries in your cloud diary:   1) 4:42 PM, 2) 5:26 PM, 3) 5:53 PM, has band of cirrus with trough passage, and 4) 6:12 PM, with some virga/ice fallout showing (darkish veils below clouds).























However, I did opine that there might be a sprinkle with this trough (see map again for example of yesterday’s “trough.”  (Sounds like the stockmarket in ’09.)  Having been specially trained to recognize virga and precipitation when a forecast of precipitation is on the line, I found it easy to recognize just how close I came to getting that sprinkle as evidenced by some virga trailing down from some of the patches of Stratocumulus clouds.  See above hills in photo at left.

You now know, if you have been reading this blog and thinking about it all day,  that ice formed in these clouds because they had crossed a temperature threshold, had gotten cold enough to form ice.  That “virga” was, if you flew through it, snow flurries.   Where it melted into raindrops closer to the ground is not visible.  However, it is unlikely that virga of this magnitude reached the ground.

You might now even guess the temperature which the tops of the clouds reached.  My guesstimate from the TUS sounding at 5 PM yesterday is somewhere between -15 to -20 C, a threshold for ice (precip) formation in shallow clouds such as these.  Estimated depth of the thicker clouds seen here? About 2000 feet or so is all.

BTW, if you noticed these very subtle virga/ice in these Stratocumulus clouds that began to show up late in the afternoon, you are a cloud observer supreme!

Yesterday’s weather map:

The end.

24 h of temperature infamy, Catalina, AZ

What an awful past 24 h here in “Catland”!  We’ve not only had low, perhaps, unprecedented low temperatures for a day with full sun, but also a noxious 15-30 mph north wind.  (Why didn’t we retire to Kauai where we would never be this cold????!!!  Just kidding, sort of.)

In some quarters(such as in a recent commentary by Al Gore),  it has been reported that we should expect colder winters as it gets warmer due to global warming (I am not kidding here-check the last paragraph here).

If this is the case, and our current godawful cold spell here in AZ has been enhanced by GW, then we had better reconsider where we grow citrus crops!  South Florida just had a record cold December.  Perhaps Florida is too far north for citrus crops as global warming proceeds and winters get colder, or at least cold spells more severe.  California, Arizona, are you listening?

Now, for a diatribe on clouds, about which Mr. Cloud-Maven person, me, is an expert (he sez).

If you saw the few small clouds we had yesterday, you saw something extraordinary for SE AZ.  Why?  Because of all the ice crystals that formed in such tiny clouds (ones called, cumulus fractus).

Below is a photo of cumulus fractus clouds forming lots of ice from yesterday afternoon.  The top most cloud is a pure cumulus fractus cloud, not yet showing ice.  But beyond that cloud, farther to the east, are similar clouds spewing forth a large plume of ice crystals, seen as the wispy, semi-transparent cloud downwind toward the right half of this photo.   Cu fra forming ice are common in the high elevation areas of the Rockies, but not here because our lower clouds that are small are almost never as cold as those, even in the wintertime.  Our clouds, according to the NWS sounding launched from Tucson around 5 PM LST yesterday were about -25 C, an extraordinarily low temperature for clouds not having any depth to speak of.   And, due to that low temperature, voila, ice forms!

So, a good eye with a little knowledge about ice formation could have guessed that these little clouds would have to be colder than about -20 C to have been so prolific in ice production, those veils seen downwind of them.  Ice forming in such shallow clouds are too small to fall out as precip as a rule, though some “virga” or flurries were observed here and there in SE AZ, such as at Stafford yesterday afternooon and west of Wilcox as well.  (Of course, I had hoped a couple of days ago that we here in Catalina would see a flurry.  Still, with flurries at Stafford, it was a damn close call, astronomically speaking, so I don’t feel that bad for getting a little too excited about the possibility of snow here a couple of days ago.  Besides, it was a “learning experience” as well….)

Amaze your friends with such trivia!!!

However, it will be a long time before you see such clouds, as low and small as these were, produce ice like this.  Well, we hope so anyway, or we are moving to Costa Rica where I will not have to experience even one second of being too cold!  If you want a really good look at what they were doing, go to the U of A’s timelapse for yesterday (here).  (Forgot to point this out until now…darn.)

Switzerland of Arizona

…sort of.  Today’s storm ended after dumping a fabulous 1.03 inches here in “Catalina Heights.”   Though it snowed very lightly here for several hours, the ground and the air were just a bit too warm for accumulations.   However, the heavy precip dumped a heavy snow cover on the Catalina mountains just  to the east.  That  snow that will be there for awhile as we enter a below normal temperature regime for the next week or two. Below, a view of that snow on the Catalinas.  Fabulous, isn’t it?

Also, as the clouds break up and with the air so clean, you have these “quilted” views of sun and shade across Oro Valley and on the Catalinas as the cloud shadows dance across the ground, another , somehow, soul satisfying scene.