Category Archives: Altostratus clouds

Sunrise and Cirrus splendor; the rarely seen Cirrus castellanus floats by

Gee, three days with a cloud or two over droughty Catalina!   Yay! Here’s yesterday morning’s nice Cirrus uncinus (icy clouds with long trails).

Then, later that morning, the RARELY seen Cirrus castellanus sporting some mammatus (downward protuberances at the bottom) showed up.  (I should note that some of the female atmos sci students at the U of WA preferred to call “mammatus” varieties, “testicularis”.)   I mention this in defference to their preference.

These icy Cirrus clouds, whatever you call them,  are probably the rarest of all Cirrus.  The noticeable cumulus-like shape shown in the second photo is rare up there.   Mainly a steep drop in temperature with increasing height up toward the top of the troposphere (the earth’s blanket of air that contains our clouds (moslty).

Turrets, or cumulus-like shapes in clouds like the “puff” of Cirrus in the middle of the second photo, are also thought to be driven by the release of the latent heat of condensation (in lower, warmer Altocumulus clouds) and latent heat of deposition in ice clouds).  When condensing droplets or as an ice crystal, heat is released to the atmosphere.  This is a HUGE factor in thunderstorms (a lot of heat is released during condensation in updrafts), frequent in cooler,  mid-level clouds such as in Altocumulus castellanus, but,  because there is so little water vapor at Cirrus levels, very unusual way up there.     Yesterday’s cloud were likely forming around -40 C,  at about 33-34,000 feet above the ground.

Below the Ci cas photo is a sounding from the folks at the U of WY.  It hints at a steeping of the lapse rate just above the 250 millibar level (between the 200 and 300 on the left side), and also just below a stable layer  or sideways “v” in the temperature trace up there.

I was quite pumped to see this rare display.   Out of thousands of cloud photos, I have but a dozen or so of Ci cas.   Unfortunately, it seemed, passersby in the Basha’s parking lot when this was about to go overhead, were non-plussed when I pointed out the unusual cloud.  They were mostly polite,  but generally said something like, “Huh?”  It made me wonder what is happening to us if we can’t get excited about a Ci cas?  I started to feel sad.

Later, in the afternoon, when the heavy ice clouds moved in (Altostratus translucidus and opacus) in the late afternoon, you probably were guessing that a good sunset was on tap.  And you were right.   Below an example of that Altostratus, followed by another neat sunset.   Likely to repeat all this today.

Hey, get excited!














The End

“Pretty in Pink”

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

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

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

Why the excitement?

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

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

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

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

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

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











“Send in the clouds”….then the wind, the rain, the cold front, the snow

Too bad Steven Sondheim wasn’t a meteorologist.  He might have written some great weather songs.  Instead, he chose to write about “clowns.”

Hmmmm.  Perhaps he WAS thinking about some weatherman in those days when he used the word “clowns.”  Who can forget that the LA Times  headline about weather forecasting in 1981;  the headline that declared that weather forecasting in the media consisted of,  “Clowns and Computers.”   Personally, I think humor has no role whatsoever when talking about weather….   Oh, well, I digress.

Today will be really exciting for us weather buffs (buffoons?)  We WILL be excited as mom Nature gives us a reprieve from the steady diet of glorious days, sunrises, and sunsets (this morning’s at left), paradise really,  with a blast of wind and then cold, likely to inflect more damage on our probably dead palms here in Tucson-Catalina-Saddlebroke.  Also this will be punctuated by a really exciting cold front passage, one where the temperature is likely to drop at least 10 degrees Fahrenheit within minutes as the wind shifts to the W  then NW after those bruising S-SW winds.  Probably here on the knob, we’ll see 40 mph or more in momentary gusts. Good-bye dead palm fronds.

When will the rain/front hit?

Well, lets say you don’t have a supercomptuer, a Cray, a Fujitsu, or access to thousands of PCs for parallel computing purposes to solve all the euqations in your 57-layer nested grid model using GFS-WRF outer boundary conditions, etc.,  for your subdomain.  What the HECK would you do, besides peruse the internet for answers, which can take a LOT of time?  Besides, we know that the internet is loaded with bad information…

Here’s what I do in this “bind.”   You get out a little piece of paper or Hollerith card (2nd photo), and you use the technique of “extrapolation.”  You got to the internet and check out the recent movement of the cloud band feature upwind of you by marking where the leading edge was, say, 4-6 hrs ago, then where it is currently, and move the two marks forward so that the back one (the old edge) is at the front of the feature and look at where that 4-6 hrs of past movement puts it  4-6 hrs from its present position.  Presently, the middle of this mass of Altostratus clouds (last photo) we have over us, will be around Noon to 1 PM using that technique.   However, there is no precip in that fat band of clouds, though one would think they would be thickening up as they approach us due to the Cat Mountains and overall effect of the Mogollon Rim.  So, maybe there will be some sprinkles around.  Our best models suggest the main rain band and front will not arrive until well after dark., and “extrapolating”, using the past 13 h,  suggests the front won’t hit until dawn tomorrow!  So, it”ll be a long time comin’, but “a change gonna come, yes it is.”

In the meantime, the biggest conundrum in today’s forecast is is what are these Altostratus layer clouds going to do (last photo), the ones at presently  zooming above us in winds of nearly 100 mph, bases at 20-22, 000 feet?  There are no radar echoes in Arizona to the west of us here in Catalina, yet as you can see they are drooping precipitation down at us in the form of virga.  As the air moistens below these clouds, as it should given the approaching system, that virga will tend to hang down lower and lower.  I would guess with this scenario that some very light rain or sprinkles will start reaching the ground this afternoon into this evening in Catalina ahead of the main rain area, the one due in well after dark. Our best model for this area is, of course, at the U of A, right here, and you can see the precip creep in then.  I think I would use them (U of A and NWS since the last time I used the “extrapolation” technique described above was in 1989 I think.  However,  you’d be surprised, when timing fronts coming in off the Pacific (where I was forecasting then), how well this simple, simple technique worked.)

Don’t be surprised if a bit of a clearing comes up toward later this afternoon to sunset.  Its not unusual to have a vast amount of quasi-threatenbing cloud go overhead all day, maybe with a few sprinkles, and then have a thin slot or brief clearing before the heavy clouds and rain move in later in the evening.  That appears to be suggested in the satellite imagery today.  We shall see! What an interesting two days ahead!

Still looks like a little snow in Catalina Sunday morning.  U of A mod indicates that the total amount of precip will be around half an inch.


BTW, while you’re digesting all of the above, here is where the weather records that were set for yesterday are.   You can see that a LOT of records were set yesterday!  Generally low temperatures and record snowfalls for the day in the northern half of the US beginning in the Mid-West and “thence” westward to the Pacific Coast.


OK, enough rambling!




“‘Altostratus'” at 30,000?”

I’m glad you asked that question.  Has to do with rules, cloud rules.   It is true that at that altitude above the ground, 30,000 to 40,000 feet, we mostly think of cirrus or “cirriform” clouds.  But those clouds, by our cloud definitions, cannot have shading during the daytime with ONE exception, Cirrus spissatus, a thick, but PATCHY ice cloud. Cirrus clouds CAN have shading when the sun is low in the sky, say, near sunset and sunrise.  Widespread sheets of gray during the daytime, as we saw over Catalina two days ago,  cannot, therefore, be called “Cirrus” unless you want to seem quite ill-informed about clouds.  Below is an example of just plain Cirrus clouds, ones that floated overhead at about 100 mph (!) yesterday.   In the first photo below, you would not be wrong, however, by referring to that thicker patch in the center as “Cirrus spissatus”, or more colloquially, “Cis spis.”

An example of “conversational meteorology” concerning Cirrus:  you and your friend are horseback riding  (as I do twice a week, really!)  and you see this scene.   The correct thing to say to your friend (in this case, “Nora”, who, interestingly,  is not my wife)  is;  “Looks like we got us some Cis spis today.  Maybe we’ll have one o’ them great sunsets again tonight.”

Well, that’s the way I would say it, anyway.  And we DID have one of those GREAT sunsets last evening that make living here in Arizona so special.  Below are a coupla shots of “Cis spis” at sunset yesterday.   (There are some other varieties of Cirrus in these shots, but I won’t bore you with a list.)  ((BTW, as an aside, a footnote, I’ve learned as a novice rider here in Catalina, that an awful lot of the guys don’t ride but their spouses do.   One husband told me, “I don’t get on anything that doesn’t have a motor.”))

Altostratus: a misunderstood cloud and for good reason

Yesterday afternoon the clouds thickened and dimmed the sun, and our high temperature struggled only into the mid-50s.  What cloud was that?  Here it is, with Twin Peaks on the horizon.

Our names for clouds, originating with English pharmacist, Luke Howard, are based on visual attributes from the ground.  Here, “Altostratus”  (As) does RESEMBLE its lower namesake cloud, Stratus, a low fog-like cloud with little definition often found in summer along the West Coast.  See a rare example of Stratus (St) hereabouts below.  Note that it is topping the Tortolita Mountains to the west, it is that low.

However, about the only thing that these clouds have in common is that they are both relatively smooth looking clouds.  Inside them, they are totally different. Also, St is a shallow cloud usually less than 1 km (3,000 feet) in depth, while As is normally 2-3 km  6,000 to 10,000 feet) in depth.  In Stratus, you just have cloud drops and maybe, as below, a few drizzle drops (mist-like)  falling out.  OK, once in awhile in cold locales you have a few ice crystals falling out, but drops rule!  On the other hand, in Altostratus, if you were flying in them with a 1998 version of the Stratton Park Engineering Company’s Cloud Particle Imager ($130,000 or so–I’ve added a link in case some of you want to go shopping now),  you would find nothing but ice crystals for the most part.  Water droplet clouds are sometimes found in them, and, oddly, if the top is not too cold (warmer than about -30 C), at cloud top, the coldest place!  So, it is not unusual to see, even in journals, a thin layer cloud consisting of drops called, As.  Makes sense really.   (A name change of As to “Altonimbostratus” would be helpful to emphasize its internal ice and falling snow particles.)

An example of the kinds of crystals found in a As clouds is shown below, collected over Barrow, AK, in a 1998 project called FIRE/ACE/SHEBA.

These typical crystals, having grown on the way down from simple plates or tiny columns, or sphere-like  “germs”, are called “bulett rosettes.”

Arizona: Colorado temperatures, Colorado clouds

It was a mind-boggling, hiking-challenging -30 F at Grand Canyon AP yesterday morning.  Overhead of Flagstaff,  at 5 AM MST yesterday it was -38 C (-36 F) and that temperature was the lowest temperature at 500 millibars in all of the US.   It is really, really rare to see -38 C over Arizona!   Temperatures in the Tucson and north area in the shallow cloud deck we saw creep over the sky from the west near dawn, were running around -15 to -17 C (5 to 1 F) at cloud top (around 11,000 to 12,000 feet above sea level) according to the Tucson sounding at 5 AM.   Bases were just above Mt. Sara Lemmon.  For those of you who think I might lie about how high the bottoms of those clouds, I present a photo of Ms. Mt. Lemmon at that time (slight hump beyond first range).

Who cares, you’re thinking?  Well, in these photos, there is a curiosity; the lack of snow coming out of the bottom of these clouds (called “virga”, and you’ll want to concentrate when you pronounce this word so it doesn’t sound like a popular drug for older males).  Normally, in the Arthur’s experience,  clouds this cold produce virga, that is,  there are natural “ice forming” aerosol particles in them that  result in snow crystal that grows and falls out of the cloud, a lot of them so that the bases of the clouds are partly obscured by falling snow.

Also there was no radar echoes around at this time.  This was to change.

Here is a 30 h loop of the radar imagery for the whole US.  You’ll have to get a microscope out or zoom in a lot to see our area of SE AZ here, but, it’ll be worth it, he asserts.  Also, turn the loop speed up to the highest level at left on this web page, or you’ll get upset over how long things are taking to view. Don’t want any “Web rage” out there!  Too, I thought it would be fun for you to see all the echoes and the things they do over a long period, in a fast loop.   You’ll see here that around AM in our area of SE AZ there is a patch of echo that develops and then kind of hangs out over us until mid-afternoon or so when it disappears.

Here’s what the sky looks like when there is widespread ice forming in the clouds and falling out, MOSTLY as virga, and when we had that little patch of radar echo over us:

Note how “smeared” the sky looks now!  Also my apologies that a bird was going by obstructing some of the sky…

Well those heavier patches that are hanging down a bit and trail off to the side is what “virga” is.  Its often more spectacular than this, I have to say.

What happened to cause this rather sudden transformation of this layer, this sky; why did all this ice begin forming in that cloud layer when it had little or no ice over most of it around dawn?

I don’t know.  End of blog.

That would be a little too honest, and so I will guess. If you’ve worked in science, and this kind of thing is your specialty, its REALLY not good to say you don/t know something.

There was a disturbance aloft that was about to come through, and I will GUESS that the tops of this layer got a little bit higher and colder as it approached.  If you saw the clearing later in the afternoon, for example, your instincts would have told you about this event.  However, after it went through, and when tops were definitely falling in height, the Tucson sounding at 5 PM MST also indicated they were slightly warmer than they were on the first sounding in the morning, and so, I am, in effect, filling in a blank, hypostulating that there was a hump in the tops that was not observed.  Oh, well. If nothing else, you might now know the difference in the appearance of the sky when ice is not present (first two pics) and when it is falling out at you (last pic).

If you want to see an action shot of all the happenings described above, here’s a movie from the U of A Department of Atmospheric Sciences rooftop of the Catalina Mountains.  My location is under the leftmost portion of this view, beyond Pusch Ridge.  This movie will take a couple of minutes to load, and is only available today (for yesterday).

The Colorado connection:  Wintertime clouds in Colorado are generally as cold as our clouds yesterday, and are constantly producing falls of ice crystals and snow when present, and so to me, a six year resident of Durango, it was a “Colorado” wintertime sky over Arizona yesterday due to the really cold air over us.

Colorful announcement of a storm

This glorious sunrise today about 7:30 AM announces in its way that a strong storm is on the way.


First of all the clouds, “altocumulus lenticularis” are the lower, rippled clouds, combined with a higher,  solid layer of altocumulus and altostratus clouds demonstrates that the air is moist to saturated over a great depth above those lowest clouds.

The lenticulars highlighted by the rising sun just above the Catalina Mountains generally occur when the wind speed at their level is at least 30-40kts.  Thus, lenticular clouds have always been a sign of being around and under strong upper level winds we sometimes call the “jet stream.” While lenticulars might hover over the same spot for minutes to hours, watching how fast the elements in it move, or other cloud movements can tell you something about how strong the jet stream is over you.  Today, the clouds were racing across the peaks, consistent with the very strong jet stream and storm systems that is about to pounce on us.  The NWS balloon sounding from Tucson this morning, a couple of hours before this shot, indicated the winds were 30-35 kts at the level of the Ac len clouds.

The second photo, kind of dull compared to our glorious sunrise, has something to say in it, too. The wind at cloud level is at the photographer and its strong,   What happens in these “pre-frontal” situations is that the air ahead of the cold front can be relatively stable, that is resistant to moving up and down, and in resisting doing that when hills and mountains are present in the path of the air movement, something akin to gigantic ocean swells are produced.  Here you see darker bases off in the distance that are PERPENDICULAR to the wind just like huge ocean swells might be.  A time lapse camera would show the movement of these “swells” beautifully as they peak and die, going through ridges and troughs, that is, slight rises and falls of the air in its movement toward the camera.

At the same time, those clouds, due to the Catalina Mountains and the higher terrain downwind from Catalina, also forces these cloouds to deepen, a process that will continue as the upper low pressure trough approaches.  As this happens, clouds such as these that are not precipitating now, start to precipitate.  The rain often doesn’t move in, but begins to fall from these deepening layer clouds overhead.  I think that is going to happen here in the next couple of hours (its about noon now).

Here in Catalina, AZ, the rainfall (17.5 inches per year) is considerably more than that in and around Tucson (12 inches per year), and this difference largely comes in winter storms like these that are subjected to the lift zone described above out ahead of the higher terrain here in Catalina,  and downwind of us.