Category Archives: Definitions

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.

Climate change: what they were saying, 1974

An early anticipation of a possible climate castastrophy

One of the great books of our time on weather modification and climate change came out in 1974:  Weather and Climate Modification by Wiley-Interscience Press. It was edited by Wilmot N. Hess, Director of the Environmental Research Labs under NOAA.   Hess oversaw 11 ERL programs.   The contributors to this book read like a who’s who of those fields back then.   The discussion of climate and climate change in this volume involves Joseph Smagorinsky on Global Atmospheric Modeling and the Numerical Simulation of Climate, Les Machta and  K. Telegadas on Inadvertent Large Scale Weather Modification, and Helmut Landsberg on Inadvertent Atmospheric Modification through Urbanization–the heat island phenomena.  The book was reviewed by numerous equally outstanding scientists of that era, some of whom are still active today.  In re-reading this volume, meant to bring a sophisticated lay audience up to date on progress in these fields in 1974, I came across this introduction to Section F on global climate, likely written by Hess,  p631-632.  Please pay particular attention to the phrase below, “..the majority of participants…” at the end of the first paragraph.

I only point this out because there has been a bit of an attempt to “re-write history” regarding what our best scientists were thinking in those days when the earth’s temperature was in decline, one that began around 1940 or so, a decline that continued into the 1970s with no explanation and counter to increases in CO2 concentrations of those days.  Much WAS published concerning CO2 and about its global warming affect, but it wasn’t being observed.  Mostly, it was just EASY to perturb the atmosphere in the crude models with something like CO2 with its well-known radiative attributes, hence, maybe get a publication.   However, not much else was known about what perturbed the exceedingly complex global climate system and caused the modest temperature meanderings, such as those shown in the third insert.

Yes, its true.   Back then (late 60s into the 70s) we were starting to think about global cooling in a visceral way based on obs.

When I say, “we”,  I am not referring to myself; I was merely a forecaster-meteorologist with in a large randomized cloud seeding experiment in those days in Durango, Colorado.  Weather and Climate Modification was important to me in the years after 1974 because of the sections on cloud seeding, not because of the climate change discussion here which I have re-discovered.  (Please excuse the highlighting, done decades ago.)

Below (third insert) is the northern and southern hemisphere’s mean temperature record as deduced by NOAA’s J. Murray Mitchell in those days; these charts appear on  p719 of this volume, and were well known at the time.  Its easy to see from these graphs why there was so much concern about global cooling in those days when you look at the decline in both hemispheric temperatures after 1940.


Another bit of interest today is the essay by Machta and Telegadas (Chapter 19, p687) in this book.  Their essay concludes with a summary by H. H. Lamb  (a well-known East Anglia University climate researcher) that contains predictions of NATURAL (emphasized by the present writer)  climatic changes and a brief evaluation of those predictions.

What was particularly remarkable was the evaluation, apparently by Lamb, in the section, “Actual Forecasts“.   In this section, seven attempts to forecast the future climate from periodicities deduced in past data are briefly evaluated.   In today’s lingo, some of these efforts might be called early detections of pressure “oscillations”, that is,  shifts in modes of circulation patterns, where high and low pressures like to reside (footnote).  These “actual forecasts”, ones that appeared in the journal literature, were based on such parameters as changes in circulation patterns deduced over decades, patterns in oxygen and hydrogen isotope ratios in ice cores that were then subject to Fourier analysis,  climate forecasts based on projected sunspot activity, another on particle radiation from expected solar flares, patterns of “meridionality” or, north and south components in the wind, and “local” circulation patterns over Europe, and that latter in a paper published in 1939!  And, of course, the old standby,  tree ring patterns, again looking for harmonics or cycles in those data.   Most of this kind work, deducing cycles in past data in the way that it was done in these papers would be taken with a grain of salt, or not taken seriously at all.

SO, WHY even mention these studies?

Lamb finds most of the predictions were CORRECT in anticipating the colder weather ahead over coming decades after these studies were published!  Its really stupefying to read this section today and see an assessment of “correct” assigned to these forecasts based on no real underlying physical mechanism, such as why did the wind, the pressure pattern change, or on sunspots?  (It was interesting to note that the sunspot based forecast was deemed “correct” for weather, but totally wrong on sunspot activity!)

Well, it does make one wonder how these forecasts could have been correct.  Were a few researchers on to something that we have missed, or have also “re-discovered”, framing our findings today in more sophisticated terms such as “oscillations” instead of “cycles”?

Or were these forecasts “correct” because they were the only ones of hundreds of such forecasts (in which it would be expected that a few would be “correct” just by chance)?   The authors of this Chapter 19 do not divulge how many forecasts were examined.

However, those early forecasts based on circulation pattern changes over decades, should grab the attention of today’s “oscillators” if they haven’t already.


Footnote:  It sometimes seems as though almost every climate researcher today has his own personal “oscillation”, from the Pacific Decadal Oscillation, North Atlantic Oscillation, Arctic Oscillation, Southern Oscillation, on and on.  More will be reported.  (Maybe I should have one!)  ((Actually, I do have my own climate oscillation, but its not been published, probably never will be.))


































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.


Altocumulus overhead; sunrise photo op coming

An upper level disturbance is going to pass over us today (see map with bend in the winds at 30,000 feet coming toward us here), but the only thing we’ll notice is some nice Altocumulus clouds floating over followed by a clearing later on today.  Those clouds are overhead now in the pre-dawn hours, we’ll likely have another one of those gaudy, too-colorful-to-be-believed-like-one-of-those-velvet-art-pieces-sold-on-street-corners-sunrises that we are known for here in AZ.  Might even have a little virga with them.   Lucky us!  So you should have your camera battery charged up in case this one’s really good!  You’ll want to add to your collection of 78,000 or so fabulous sunrises and sunsets in Catalina, AZ…like I will.

Note, too, that in this depiction of winds (the wind is flowing along the lines) that where the wind has a “U” shape, there are clouds to the east of those bends for the most part, that is, ahead of where that “U” shape in the winds is headed, and not much to its rearward, or in most cases, immediately to the west of the “U” bends in the winds.  We will see the “ahead” portion of a “U” in the winds above us, and the clearing that comes afterward, all today!

The end (for now).


How Cirrus clouds grow up to be “uncinus” ones

What a glorious day yesterday was, if about 20 degrees F below normal!  So much new snow on the Catalinas down to such low elevations for almost mid-April.   Some sites in the Catalina Mountains reported over an inch of water content in that snow!  Yay!  Here in Catalina we had a bountiful 0.69 inches, more just to the north and west.  Choose April 9th, and “Tucson” in drop down menu on this U of AZCats rain page to see the amounts around here.  Truly a remarkable storm for April.

About those Cirrus “uncinus” clouds

How many saw those fabulous Cirrus clouds in the morning?  Once in awhile, during the passage of Cirrus clouds you get to see how those long, delicate strands you often see by themselves, get that way, from their initial appearance to the end point;  the long strands.  Usually you can’t because Cirrus clouds are traveling so rapidly up there at 30,000 feet or so that they have gone over the horizon before much happens.   Yesterday, an example of that “life cycle” passed overhead, moving from the W to the E at about 70-80 mph or so.   In all of the photos below, the subject Cirrus cloud is in the upper right part of the photo.

Here then is most of the life cycle of a Cirrus cloud as it happened over Catalina.  The starting point is that whitist cluster of little cloudlets, upper right.   Those strands of Cirrus below that and that appear in rows to the lower left, are old dying cirrus clouds at the end of their life cycle.   That top cluster in 1) has just appeared, probably only about 10 min old, and now the larger ice crystals are JUST beginning to leave the origin zone, much like a hiker reeling out rope to a friend stuck on a rock below.  Those strands are like that rope having been let go of, then caught by the wind on its way down and stretched to full length while falling through the air.   The remaining photos 3)-overhead view and 4)–leaving the scene, show that process continuing as the top cluster fades with longer and longer filaments of ice.  In 4), you can see one strand in a side view as it speeds away revealing the lack of wind shear (changes in wind direction and speed) in the layer in which the cloudlets first formed.  How do I and you know that?  That one tiny filament that is straight up and down pretty much reveals that

You can now see how and why these delicate strands are there.  Each long “rope” of ice represents one of the initial tufts that appeared within the cluster; each one has a contribution to make, a “rope” of ice to send downward.  Almost always, except in deep storms, the strand of ice encounters drier and drier air and the crystals fall at lower and lower speeds until its negligible.   The bottom, or lowest part of these strands then, have the tiniest of ice crystals, and the tail of the strand at this lowest point may appear almost horizontal if you could be up there.

The end.


“Stuck Inside of Tucson with the Seattle Blues Again”

Paraphrasing Bob Dylan’s song title, one that had the line, “Stuck inside of Mobile with the Memphis blues again”, that great, driving song he did in the 1960s.  See photos of Seattle-like conditions of low-based Nimbostratus below with a temperature of only  37 F (!) right now in Catalina!  Egad.   As you can also see, after 0.39 inches of rain up until about 11:30 AM this morning, there is also some flooding going on.

(Of course, me and most Arizonans really LOVE rain; it’s to be treasured at all times!  In Seattle, where I just spent three weeks, not so much.)

Local weather for Catalina here.




Some iridescence with your clouds? And a photo comparison of our current droughty conditions compared to last April’s green

Yes, we had some yesterday evening in those Altocumulus lenticularis clouds or just “clouds” for most of you.  This delicate “rainbow” coloring in last evening’s clouds is due to the diffraction of light around really small cloud droplets, ones that have just formed, a few microns to 1o microns or so in diameter.  Because the droplets have to be “really small” to produce this effect, iridescence is almost always located at the upwind edge of clouds that thicken downwind, as these do.  It was more colorful than I could photograph, but here are a couple of shots of that phenomenon we call cloud iridescence, or irisation:

By the way, the winds at cloud level here (around 2o -22 kft above the ground and at -30 C or so) were just about 100 mph (85 knots) at this time as that huge trough over southern California edges closer to us.  Unfortunately, it is “ejected” to the northeast out of southern Cal this morning and that means that this whole upper level system will be moving faster and faster as it moves toward Arizona and then into the Plains States.  That means that the band of rain generated with this system will be moving through at a faster pace and for that reason won’t produce as much rain as it might have if the system was not speeding up.  Still, looks like we should get, here in Catalinaland, around a quarter to half an inch.  Very exciting, since it will do what vegetation we have some good.

Free range grazing land now down to about just dirt, as little of the spring grasses have poked up before being ravaged by hungry cattle and native wildlife.  Kinda depressing after last spring’s bountiful display of grasses and wildflowers.  I have contrasting photos below as well.  You won’t like what you see in this comparison because it brings our droughty winter into sharp focus.   What is nice about our desert is that the mesquite and acacia bushes/ trees don’t seem to care how dry it is and are still are intensely green this time of the year, some consolation for the lack of green elsewhere.

You also may be struck by how tall I am, perhaps I played basketball in college you wonder.   In the first photo illustrating the dry conditions, I am apparently several feet taller than my wife, Judy, who walks ahead of me with Zuma, one of our dogs.  I guess I could have been on stilts, but I am actually on our horse, Jake, and am not that tall FYI.

The end.



Cirrus uncinus display; the tops of storms made visible

First, some instructional material:  You should be looking for your camera now, as seen in the first shot! Those Cirrus clouds to the SW are moving at you rapidly (95 kts, 115 mph at 30-35 Kft ASL!), and so there’s not much time!  In this first shot you can already detect some Cirrus uncinus, Cirrus clouds with hooked, or tufted tops in the center, with long icy strands trailing to the left. At this point perspective makes them bunch together so that they may not appear that “photogenic.”  However, just wait!  And, it was worth waiting just a few minutes for.

Take a lot at which they looked like passing overhead in the second and third shots, only about 7 minutes later. Just magnificent, some of the best Cirrus uncinus examples I have seen.

What is interesting about these clouds is that you are getting a glimpse of the structure of “stratiform”–that is, steady rain and snow storms that happen every day around the world, except that here in these photos,  you are only seeing examples of the very tops of them. Those widespread rainy/snowy storms are usually packed with thousands of these kinds of clouds in a solid overcast up there, each “cell” shedding tiny ice crystals which then waft their way down, growing, perhaps merging into “aggregates” of ice crystals we call snowflakes, and, that most of the time except in Wisconsin in the winter, melt into raindrops as they fall below the melting level.  Chances are, our little snowstorm of a few days ago had tops just like this.

Sometimes, clouds like these, and returns from vertically-pointed radars that can detect clouds like these, are referred to as “generating cells”, for obvious reasons.  The trails you see here are clearly visible on very sensitive “cloud sensing” radars–they are not visible on “First Alert” Doppler style radars and such used by the NWS because the ice crystals are too small at this point to produce a return on “normal” radars.  These cells form in a relatively shallow layer that usually lacks wind shear, likely mixed out by the little up and downdrafts in it.  Its only after the crystals fallout that they encounter wind shear and end up being stretched out into “tails” as here.

Falling from heights of 30,000 feet takes a long time, for an ice crystal falling at only around 0.5 meters per second or around 1.5  ft a second or even less.  It will take  LONG time for anything to reach the ground, perhaps 2-3 hours to reach the melting level.  So the little generating cell that produced a ice crystals at the top of major storms that grow and merge into snowflakes is likely over Alamosa, CO, and points northeastward by the time that flake landed on you at the ground with upper level winds such as we had yesterday.

I think its kind of interesting, but I may be the only one!

The end.

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.