Author: Art Rangno

Retiree from a group specializing in airborne measurements of clouds and aerosols at the University of Washington (Cloud and Aerosol Research Group). The projects in which I participated were in many countries; from the Arctic to Brazil, from the Marshall Islands to South Africa.

0.04 inches is all

Well, it was reel good to get some rain, but we were SO close to a big dump!  Of course, the sophisticated reader will have noticed right off the air was larded with Floridian-style humidity yesterday morning.  And what was the other sign for great (large) clouds immediately in front of you?  Clouds topping Mt Sara Lemmon1 or even lower elevations of the Catalina mountains.   Here is a short of those early raggedy, small Cumulus clouds, in case you missed them and wanted to see them again:

What was interesting is that not much growth in any of the local clouds occurred through about noon, though they filled in the sky some.  I decided to go to a movie at noon, rather than face the disappointment of just shallow clouds all day yesterday;  I had opined to friends around dawn on a horseback ride that when you see clouds topping the Catalinas it is a near sure sign of large clouds and heavy showers around later in the day.  They might not land on you, but they will be there.

But nothing was happening through noon to indicate that it was going to happen.  But what a change in the sky when I got outside at 2:30-3 PM!  Huge Cumulonimbus clouds here and there, big, icy anvils everywhere, growing Cumulus all over, too.  I will never again go to a movie and miss a change like that.

Here in Catalina, we came SO close to a major late afternoon gully washer.  Check this sequence out.  Looks like regions of Catalina State Park got the core of this dump.  The dark, solid base of this cloud (a good indication of a good updraft above you) began to extend westward and over the south part of Catalina and our place!  I waited for the HUGE first drops to fall out, as they do under such bases like this. “Hit Me With Your Best Shot!”, I screamed at the cloud, recalling the words of Pat Benatar.  “Drench me, baby!”  I waited and waited, but it drifted away toward the S, towards Pusch Ridge, and that darker part never did drop rain.  Cargodera Canyon, NE corner of Cat State Park reported the most rain (reports), but only 0.16 inches.   That amount would not have even been close to the maximum amount dropped by the shower in the photographs below.  From the writer’s storm chasing days with his trusty raingauge, at least 0.5 inches fell.

BTW, if you are driving around seeking maximum rainfall amounts from the initial dumps like these because you are upset that they don’t get recorded by in-place gauges, and you feel YOU MUST GET OUT OF YOUR CAR to plant your raingauge, do so only immediately AFTER a lightning strike.   I shouldn’t even be writing this kind of thing since it drastically conflicts with NWS lightning rules, but that’s what I did when I storm chased in this area many years ago.  Silly boy, maybe lucky to be writing this today!  So, don’t even think of doing this really;  mount your gauge on top of your car!  It’ll look great there.

With the Floridian air mass still in place, another day of sights like the ones below are guaranteed.  Maybe today Catalina will get its share of the liquid bounty!

 

 

 

 

 

 

 

 

1As a heterosexual male, I like to point out that Mt. Lemmon is one of the rare feminine mountains, not the usual male mountain, as a nod to women everywhere.

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.

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:

Peachy!

Sunset, anyway, even if only a few drops of rain fell last evening.   Nice lightning to the south, too, 9-10 PM.

However, yesterday afternoon, we had some examples of really “bad” cloud bases.  They were trying to make me think we might have a repeat of the day before’s cloudburst by darkening themselves up.  While Mr. Cloud Person (me) was almost fooled, he wasn’t really at all.

Lets replay yesterday afternoon….  Here in the summer, of course, we look to the east (NE through SE) and over the Cat mountains for guidance in storms, for prognostic purposes, not to the west during the summer rain season.  This is especially true in the late afternoon and evening when our chance of rain is peaking.  We often see the sky loading up with dark cloud bases somewhere over there.  Its pretty darn neat, and can happen in only a few minutes. These are often storm complexes, clusters of Cumulonimbus clouds,  that done sprung up over the White mountains or other terrain earlier in the day, and are being re-inforced/ are propagating westward by the outflow winds that accompanied them.  Those winds near the surface shove the air above it upward creating new clouds.  Sometimes we’ll see an especially low cloud on the more moist days, called an “arcus” cloud, a ribbon of cloud that rides above and near the front of the outflow wind.

OK, those clouds that feinted rain late yesterday for a time.  First, we’ll start when you were getting really excited and running around telling the neighbors that, “Hay!” (a lot of them have horses), “It looks like it might rain again this evening!  Look at those clouds over there over the Cat mountains!” You’re loud, but you’re not exactly screaming, since you are holding back a little; you know about those “fakery” cloud situations where the bases fall apart, don’t congeal into a large, solid mass.   You’re holding back just that bit of excitement.  I am proud of you.  Here’s what got you going:

This is looking pretty damn good, but its not there yet.  Why?  First, while there is an OK, keep an eye on base over the Cats, its got some thin spots, some brighter areas near the darkest areas.  Note the little bright spot in the middle of the closest larger base.  Fakery right there.  You know this cloud is not going anywhere in spite of its overall darkness underneath.  Also, you really don’t see any sharp edged indicating newer) rainshafts.  Blobs of smooth sky, even with rain, are associated with dying cloud masses, and if that’s what coming at you, you may not get ANY rain because it may have all fallen out before it gets to you with our slow summer winds up “top.”

The next photo is 20 minutes later.  Its look that bit better, but in all that time, no rainshaft has dropped out of this stuff.  Nor has the cloud complex gotten much closer.  No rainshaft equals no cloud tops colder than -10 C (14 F) above that base (about 20,000 feet yesterday), and that means while dark, the clouds are not terribly deep.

Why aren’t they yet?  Not enough push underneath, warmth, etc.  This lack of progression is of some concern.   Of course, this can change in a hurry, but increasing concern develops that this could go bad.  A lot of time with not much happening is quite bad, really.  The next photo is about 6:19 PM.  While the cloud base is looking formidable, still pretty solid, a rainshaft has STILL not developed indicating cloud tops are going nowhere, man!  Dammitall, to cuss that bit! Starting to get that “rejected” feeling:  “Well, you thought I (that vaporous mass) was going to do this, but I’m not.”  You think about the screaming you did at your neighbors…  Could be embarrassing. In the last photo, ten more minutes later, its over, finished.  The cloud base has shrunk in size, is starting to look raggedy, still no rainshaft, etc. etc.  You begin thinking of this cloud fakery in terms of spheres of equestrian processed hay.  But, you did hold back that bit, you didn’t go all out because you had seen this happen before.  I am proud of you.

The End.

Yesterday’s Catalina-centered blast dump: 0.83 inches; 0.53 in 16 minutes

Nice weather we’re having lately.   Nice desert greening we’re having now, too.

What a day yesterday was!  Look at the sunrise view of Altocumulus at the start of the day.  And, too, how about some neat patterns before all the mayhem.  What a day, to repeat.

Yesterday’s blast and dump that struck just after 2:30 PM yesterday can be seen in a side view here, courtesy of the University of Arizona Wildcats Department of Atmospheric Meteorology.

Watch those dark cloud bases move over the southern portions of the Cat Mountains at 2:30 PM in this time lapse film!   Pretty dramatic, and also see how fast a cloud can drop a load of precip its been carrying in some of those around Tucson yesterday.

Below is what those same clouds looked like rolling over the Cat mountains toward us from our Catalina vantage point.  This was pretty darn exciting to see!  Why?

First, that dark line of bases was streaming toward Catalina from Table Top peak.   Next,  the bases are pretty large, meaning a there is pretty large area of updraft, and 3) MOST importantly, the bottoms looks solid, no bright spots interspersed among the dark base telling you that the updraft has holes in it.  A solid, contiguous base like this suggests a good AND contiguous updraft, and a LOT of water is being condensed above those bases.

Can things change and holes develop even at this point?

Yes, have been horribly disappointed a time or two when that has happened, and when it does,  its kind of like the beginning of a love affair you thought was going to be a good one but goes  “south” all of a sudden because you made some assumptions based on too little “data” and other misinterpretations due to wishful thinking and delusions and then you find out that those assumptions and perceptions were incorrect and you REALLY were delusional cum laude.    How painful is that?  But then you have to “man-up”,  as we say today, and pretend that nothing happened…or you’ll lose face.  Yes, I have had to do that with some cloud bases that have let me down.

Or taking another tact here for sports fans, a cloud base that falls apart is like a seeing a running back breaking into the open, with a clear field ahead.  Everything LOOKS good until he trips and falls at the 10 yard line.   You’re so upset, you go down to the Golden Goose thrift shop and buy a pair of ladies’ used tennis shoes and send them to the miscreant running back as a way of pointing out your displeasure.  You don’t want to admit you were wrong in your “a priori” assessment that a touchdown would surely be scored.

Well, you get the idea.  It can all go bad just from looking at the cloud base and making an “exterior”  assessment because you really don’t know what’s happening “above” (as in people).  So, you have to “hold back” your emotions just that bit to keep from being hurt by a nice “cloud base.”  Was I talking about weather somewhere in here?  OK, back on task.

But that cloud base yesterday did not fall apart; it did not disappoint!  Rather it remained solid until that magical point that all that water/hail/graupel up there above the bottom of the cloud begins to shoot down, often in strands or filaments.  The strands or filaments are almost always due to hail or graupel shafts.  Hereabouts they are likely to have melted into large drops on their way down.  (When flying through these kinds of clouds, as the writer did for many years with the U of WA Cloud and Aerosol Group, flying through those miniature shafts of hail/graupel (soft hail) was like someone throwing a handful of rice at the pilots window.  They were only tenths of a second in duration, maybe 10-30 yards (meters) wide.   Its still not clear what cloud “microstructure” and circulation leads to such tiny strands within large clouds.  Uh Oh, getting deep here.

Check out the next couple of photos, especially number 2 and 3.  For maximum precip excitement, I would have, and I am sure you, too, wanted to have been about 1 mile farther toward that base as the bottom drops out.  That’s where the largest raindrops, hail or graupel are going to be.  Of course, all that water is going to shove a lot of air out of the way, and that’s why we saw those momentary blasts of wind to 50-60 mph, at least right here.

Here’s a map of the local area rainfall, thanks to the U of A rainlog organization.  It will show you how well we did relative to the rest of Tucson.

 

The End.

“Back in Black”, cloud bases, that is

Few people know that Angus Young, lead singer for AC/DC, was quite the weather nut and many of his songs, such as “Back in Black”, are actually about clouds and storms.  Thought you’d like to know so that when you get your old AC/DC albums out, they’ll have a little more meaning to them…  What about the AC/DC song, “Hell’s Bells”, you ask?  Its interesting that you have asked me about that.   Here’s the story behind that one:  well, that was about a forecast of rain that didn’t materialize there in Australia. Its mostly desert there, like here.  Mr. Young was pretty upset about it, apparently.

Some cloud bottoms for you from yesterday.  Nice to see the return of the summer rains.  Only 0.07 inches here, but I was quite happy to see that heavier showers fell elsewhere,  all around me,  in fact,  and perhaps in droughty areas that needed more rain than I do (face turning red, fist pounding table).  No, it REALLY was good to see others get more rain than me, and watch the summer “spectacle of the rainshafts” way off in the distance underneath those Cumulonimbus clouds.  I like spectating rather than participating, that is, being inside those rainshafts (face turning red, fist pounding table).

On with the picture show:

 

 

 

 

 

 

 

 

That sunset scene last evening;  the slot of clearing that allowed the yellowish sunlight to bath the rocky faces of the Catalinas, followed by sunset color in the underlit clouds overhead. Can one’s thoughts not shift away from self and problems, to the joy of being here in this special place?

The End.

Lenticularis in July?

Altocumulus lenticularis, to be exact.   Of course, as the discerning, eruditeful cloud person that you have become, I didn’t need to tell you this.

Well, yep, here they are, courtesy of the U of A Wildcats website. And, if you missed them locally near Catalina, here are a coupla shots.  In this movie, you will see sliver clouds that appear absolutely motionless above the Cat mountains.  Those sliver clouds are “Ac len.”   Cloud droplets form on the upwind side (to the right) and evaporate on the downwind side (on on the left) in this film.  They are stationary because they are in a bump in the airflow caused by the mountains, and since the mountains aren’t going anywhere very fast, the bump remains in the same location as long as the winds are steady.  As the air moistens and dries out, those Ac len clouds can expand upwind or disappear since the bump or hump in the airflow is bigger than what you see when the air quite dry.  I will get my 1o1 cartoon of this situation out. (I actually taught 101 one summer at the prestigious University of Washington’s Department of Atmospheric Sciences.  Poor students!  Those weather jokes!  Poor University, too.  I had,  and have, only a Bachelor’s Degree and I am sure that this Lectureship caused a decline in Washington’s accreditation that year.  As you know, to teach even the most simple class, a University must have Ph. D.’s. Experience gained in research and in the “school of hard weather knocks”, etc.  have no real impact on a university’s accreditation as we know1.  Gotta have the big Ph. D.  Whining here, and off task, but it feels good.

Lenticulars are an odd site for July.  Why?  Because lenticularis clouds are associated with stronger winds aloft AND a modicum of moisture and we don’t usually see BOTH in July.   However our influx of tropical air, not fully arrived yet, is associated with a stronger than usual flow pattern.  The NWS rawinsonde (balloon) sounding indicated winds of 30-35 mph at cloud levels.  Here’s what the sounding looked like as depicted by the University of Wyoming Atmos. Sci. Dept.:

Where the dark lines pinch toward each other are where clouds might have been.  Since at sunset some of these Ac clouds shed ice, you would have to guess that they were NOT at the lower level where the lines pinch in  (“600” mb or 14,000 feet or so above sea level) but rather near 20, 000 feet (or at the “450” mb level or even at the “325” level, close to 30,000 feet (!) that highest point where the lines pinch in showing a moist layer.

Quitting here, looks like first chance for rain today after the interruption of the summer rain season….  Excellent!  Gorgeous sunrise “blooming” now, too.  Ac opacus with scattered virga.

 

 

 

 

 

 

 

 

 

 

Below a simple diagram modified for the Catalina mountains showing what the airflow might be like under strong, semi-moist westerly flow with Ac lenticulars occurring downstream from the peaks:

Catalina summer rainfall 1977-2010: there is no trend

OK, no fooling around today with HUGE text boxes with book length ramblings, just the facts:

Catalina inches of summer rain

These data again mostly due to the friendly folks Wayne and Jenny down at Our Garden here in Catalina.  Since they are open today, Saturday, it would be great if you went down and bought everything they had as a gesture of appreciation for collecting weather data over so many years.  Its really invaluable since there are no other data in this area.  The data for 2008-2010 are from a gauge here near  where the pavement ends on E. Golder Ranch Drive, or at a somewhat higher altitude than the earlier measurements.  Note the lack of a trend, not getting droughtier in the summers. Yay!

Its always fun to look at past data and dream about excess wetness, as we had here in for two summers in the early 1980s.  Imagine, in 1983,  June through September logged over 17 inches of rain!  Our annual average is about 17.5 inches here in Catalina.  Note this annual average is considerably more than locations that are relatively close where in general, averages such as at Tucson are closer to 12 inches per year.

Clouds!

A welcome sight was a few evening Altocumulus clouds creeping past the Catalinas yesterday as tropical air begins making its return.  Mods have rain in the area beginning tomorrow and continuing for several days at least thereafter.  We’re just beginning the height of the summer rain season (sorry, I can’t say “monsoon”;  monsoons are in India and SE Asia.   We don’t call hurricanes,  “typhoons” do we?  Never mind;  just don’t like “monsoon.”  Its a quirk.  We all have them, so I don’t feel bad at all having quite a few quirks.)