Cirrus and Altostratus ice clouds today; dust and sprinkles ahead

Being a fussy type, I will complain that the sky has not been quite right lately with a continuing, though slight,  smoke layer aloft.  The sky has not been as blue as it should be.  A couple of days ago when it was windy, it was good ole’ Arizona dust made the sky not so blue,most of that brought in from the northwest of us.  Dust as a rule, is not up high in thin layers like smoke can be.  Dust particles are usually too big for that (several to 10 microns or so in size).  They fall out quicker.  The period in this sentence,  font size (12),  is about 100 microns.  Hmmmm.  Wonder if that translates well to your screen?  Probably not.  Oh, well.

Today, however, we will see some interesting Cirrus clouds (it’s dawn now and they’re already here), probably some uncinus types with tufts and long interesting twisty trails hanging down.   Later, before the clearing, these ice clouds will likely be thick enough to call them “Altostratus”, those ice clouds thick enough to produce widespread gray shading.  Only one kind of Cirrus is allowed, in our cloud definitions, to have gray shading and that is the species, “spissatus”, and they can only be patchy clouds that don’t cover a lot of the sky like an Altostratus cloud would.

Here’s where you can see this hook shaped arc of Cirrus coming at us in this 24 h loop from the University of Washington Huskies Weather Department.  Also, you can see it on this map below, also from the Huskies.  Of course, this is a “man’s” (read, adult person’s) weather map, not one of those Mickey Mouse types you see on TEEVEE so much.

What’s the payoff today?  A great sunset as the back side of this blob of ice clouds should be over us by late afternoon.  That will allow the sun to underlight the bottoms of the Cirrus-Altostratus clouds, the latter likely with virga which will add to the effect by having something like stalagmites hanging down in that underlit time.  Well, we are out on a limb here with so much detail, but that’s what I would hope for.

Dust, then sprinkles ahead

In the meantime, the models have been revving up the strength of a trough of cold air headed this way.  Tomorrow it generates the dreaded Tonopah, Nevada, low pressure center, and again, as last week, it will be intense, lots of isobars around it.  Lows like to nest around Tonopah and so that phrase, “Tonopah Low” has been around for decades.   Tomorrow, as the wind picks up in the afternoon, you’ll see the usual coating of dust start to build up on your car, etc.  I wouldn’t wash it until Thursday.

That’s because now, the jet stream at 500 millibars (18,000 feet above sea level or so) will finally get a little to the south of us, and the wind maximum at that level marks lower clouds and precip to the north, and much drier air to the south.

As that jet passes over us tomorrow night, it should mean that by Wednesday morning we have some lower clouds like Stratocumulus and Cumulus a plenty, and with the lower freezing level that comes with troughs, those clouds should be able to produce ice, which in turn means snowflakes that melt on the way down into raindrops.   Well, really stretched that out.  But, then again, I am not a TEEVEE weather presenter who would short change you on technical explanations because they think you are too dumb to take it.  Oops, going over the line here.

Enjoy 1) the sunset. 2) the dust tomorrow afternoon and evening–really, there’s nothing you can do about it; 3) some “glaciating” clouds on Wednesday, maybe with enough stuff coming out to produce a few hundredths even.  Fingers crossed.

Blue skies back; some more of that Catalina rain climo, March this time

Feeling better now that the K-layer has moved on and our skies have returned to their normal deep blue. (“K” =s smoke in meteo-parlance, not a strikeout.)

No rain in models for southern AZ next 15 days.   Ugh.

In the meantime, as filler material, I will bore you with a graph of Catalina March rain climatology, thanks to our friends at Our Garden who, frankly, are a bit weather-centric.  Remember that if you buy stuff there, you will actually be supporting weather activities.


 

Nice temperatures; bad sky

That was an awful sky for Arizona yesterday.  Thank heavens those kinds of days are rare here.   Here are a few more shots of that rare smoky layer day yesterday, including one at sunset where you can see some undulations in the layer.  You may have noticed that as the day wore on, the smoke appeared to be getting lower, and starting to reduce the visibility toward our mountains.  At the beginning of the day, the layer was well above any mountains around here; there was no apparent haze whatever below that layer.  There is a tendency for layers of smoke to lower with time, much as middle and high clouds do before storms, and that was part of it, as well as a tendency to mix downward as the day warms up.

 

 

 

 

 

 

 

Of course, if you’re from back East or from southern California, you’re wondering, “What’s the problem?” You see much more haze and smoke (smog) than this all the time. Heck, back East in the summertime, its so blasted hazy in the humid air before a cold front cleans it out, that you can barely detect that the sky is blue!

Here are examples of what smog looks like, first, over Virginia from on top (yuk), and second, on the ground at Chincoteague Island (also, yuk).

So what’s the problem?

We don’t like you’re kind of sky here in Arizona, even when its not that bad.

 

 

 

 

 

 

 

 

 

 

But heavy aerosol concentrations indicated in these last two photos help cool the earth off.  Here is more from NASA’s Earth Lab about that if you’re interested.  Would you like a cooler earth in which you can’t see the sky and mountains, or a warmer one with a blue sky? Well, a warmer one with blue skies is why I moved to Arizona!

Again, back trajectories for air arriving at 4 km and 6 km above ground level over Tucson (about 13,000 and 20,000 feet above us) suggest that the smoke is coming across the Pacific from Asia.  Here is another plot ending at 5 PM AST when the local photos were taken.

We can hope it will be gone today as the trajectories of the air coming over us begin to change.

The End.

Smoke layer aloft today

If you got up today, or even late yesterday afternoon, and got a feeling that the sky was “not right”, you were right!  We have a well-mixed smoke layer above us, “well-mixed” meaning you don’t see any gradations in it.  That in turn, means its been up there for a LONG time, and the gradations have been mixed away by turbulence. (If it was from a fire even as close as California, you would probably notice thicker and thinner portions of the smoke.)

Where did the smoke layer over us come from?

Probably from northern China or Russia.  Haze can be lofted to high levels and then can race across the Pacific to the West Coast and beyond in the jet stream.  Sometimes its even dust, but that’s a little more unusual than smog, that is, smoke and haze from regular pollution from urban areas and fires.

Below are backtrajectories for the air over Tucson ending at 5 PM AST yesterday afternoon just as the smoky air was arriving over us.   That was the latest global dataset available for this calculation from NOAA’s Air Resources Lab.   Estimating that the smoke layer is at 16,000 feet or higher, backtrajectories for three levels above the ground are shown, ones between for 16,ooo, 22,000 and 30,000 feet above the ground.  The calculation goes back four days (96 h).  The star is where the air trajectory ends, over us. (Note:  you can make these yourselves, BTW, at the ARL site using their Hysplit model.)

You can see that the air over us yesterday afternoon, and certainly today as well, came from Asia.  The model thinks the haze layer was already at a high level (look a the height of the air four days ago in the lower elongated graph) while exiting Asia.   So, this smoke layer is no doubt from even farther west east Asia

BTW, if you were on a plane departing or arriving in Tucson yesterday or on one today, you would doubtless pass through this smoky layer and see it as a thin  black or dark brown line.  Maybe you could ask a stewardess to ask the pilot or pilotess or his/her many helpers up front to tell you the level at which he passes through the thin dark line.  I would, certainly.  But usually nothing happens….  Oh, well.  Below some “just in shots” of the not-so-blue-sky.  The whitishness of the sky is caused by “forward scattering” of the sun’s light off the tiny aerosol smog particles.  “Back scattering” from these particles,  when you look at the sky opposite the sun, is pretty nil with smog particles, and so the sky doesn’t look quite as whitish as toward the sun, but its not the intense blue we should have.

Yes, we are a global community of smog producers, and here is one example.

 One caveat.  It is possible that it is dust from Asia rather than smoke.  It is a little difficult to tell for sure from the ground, but right now it looks like smoke to me.

The End.

Whiff


How sad.  A few contours to the south of us, that jet to the south of us, that is,  and we’d have got our tenth or more inch of rain.  But no.  That trough over southern California and northern Baja had to zip out and “up” (that is, to the northeast) like a jet taking off from an aircraft carrier.  Gone now.  All we’ll have is leftover wind and a threatening looking, but too shallow a deck of…….Stratocumulus.   Too warm on the top of this layer this morning for ice formation, and that, as you know here in AZ, means that nothing comes out the bottom because the droplets in the cloud are too small to fall out.

But yesterday afternoon, an ice bonanza!

Alas, those Cumulus and Stratocumulus complexes were too high-based for the considerable ice crystals and snow forming in them to reach the ground as melted drops,  except for “sprinkles-its-not-drizzle” here and there1.  Heck, the drops that made it down around 5 PM AST weren’t even that big.

I wonder if you saw the rapid transition to ice-producing clouds yesterday.   Not much going on up to 1:30 PM.  Then, all of a sudden, it seemed, there was ice almost everywhere in those little clouds.  It was fascinating since they did not appear to be deepening upward to lower temperatures.

Let’s review yesterday with a long cloud harangue, starting from that wonderful sunrise with an Altocumulus lenticularis undulatus (has something like ocean waves or rolls in it to produce this where the air is rising and falling to produce cloud, then clearing), here is yesterday.  Hmmm.  I wonder if you remember where THIS sentence started?

Next, that promising scruff of cloud (I would call it, Stratocumulus) topping Mt. Sara Lemmon.  It was promising because with cloud bases lower than the top of Mt. Sara, there’s a better chance of rain reaching the ground.  But, up they they went as it got warmer, a usual thing.  Has to be a flood of water vapor coming in to overcome the rise of cloud bases with daytime warming.   As boffo as that trough looked over southern California, it couldn’t really “bring the bacon” if bacon was moisture that is.

We did have a lenticular cloud, too, for awhile.  Let’s see that, too.  It will be good for you.  Notice how it is near the same spot as the “undulatus” cloud?  That’s what lenticulars do; they have favorite haunts.  When the flow is from the southwest, this is where they are going to be, over and over again, downwind from Mt. Sara L.

 By mid-day and early afternoon, Cumlus cloud bases were well above Mt. Lemmon, a couple of thousand feet at least.  Here is a mid-day shot of those non-ice producing, Cumulus fractus and humilis clouds next.

 

 

The first Cumulus photo was taken at 1:50 PM, and if you were a real sharpie, you would have seen some tell tale vales, but probably only Mr. Cloud Maven person did, they were that faint.  But here in this second shot of Cumulus humilis and such, you can PLAINLY see that in the center, one of those little guys has converted COMPLETELY to ice.  It was pretty amazing to see that in such small clouds.  Soon the whole sky was filled with clouds “icing out”, becoming nothing but ice crystals and snow flakes.  Here are some more photos of that stage, including a short rainbow demarcating where the snow was melting into drops.

 

 

 

 

 


So what caused all the ice to appear in clouds that didn’t appear to be growing in height?  Well, first of all, by the end of the afternoon, they were certainly colder at cloud top, so that would explain the late afternoon ice everywhere.  Also contributing, was that is was getting colder over us as the day wore on as that trough approached.  So, even if the cloud tops stayed the same height, they would have gotten colder.  Finally, dust has been known to have a role in causing clouds to glaciate at higher temperatures than if there was no dust getting into them.  This is something that we saw happen in Durango, Colorado during a randomized cloud seeding experiment when dust storms hit and “ice nuclei” measurements shot up.  So, dust, too, may have had a role.

The afternoon TUS balloon sounding suggested that the tops were only about -15 C (5 F), maybe -17 C in one that momentarily bulged above the main cloud top level-Cumlus clouds do that.

However, the amount of ice is not commensurate with a temperature that “high” and so I reject the sounding temperature.

I think, with bases around -10 C yesterday afternoon, that for clouds to produce as much ice as we saw, they would have to be -20 C (-4 F).  I think maybe the strong temperature drop to the northwest from the balloon launch site might have played a role, that the temperature of the balloon instrument was correct, but it was a few degrees colder over Calalina and to the northwest of us.  That “surmision”, a deduction,  you get from, say, the 500 mb map where it was far colder at Flagstaff than here.  Of course, you might think I am lying, and just made that last part up because I am really clueless about what happened.  Due to your doubt, I will now post the 500 millibar map from my home university so that you can see I did not make this up.

As you can see, while TUS is only at -18 C, Flagstaff is -23 C, and San Diego is -28 C!  So going to the NW (a heading of 310 degrees) from the balloon launch site their at Davis-Monthan meant it was a LOT colder in that direction, mile by mile even maybe.   Also, you can see by Flagstaff’s wind, that the jet core at this level had not passed over us, a key to wintertime rain here.  Never did.  Hence, a “whiff” on this storm, to use an old word right before a new word from baseball, as in, “he whiffed on that slider” (struck out). I can’t believe how I am educating you today!

The End.

————————————————-

Sorry, have to carry on this theme about what is drizzle and what’s not.  You should find another TEEVEE weather presenter if he or she calls what happened yesterday for a few minutes, “drizzle.”   Rain and snow mixed is NOT “sleet”, by the way, either, another looming corruption of our weather terminology.

Windy; slight rain foretold overnight

Doubtful to me, but a tiny amount of rain (less than o.10 inches) is foretold by the  massive U of A Weather Department Beowulf Computer Cluster for Catalina overnight.  Check this out.  Would be very nice, even if just a dust settler.  BTW, you should wipe down your rain gauge collector funnel since all the dust from the past few weeks might prevent some drops from rolling from the outer collector into inner magnifying tube.  Hey, maybe some WD-40 on the collector funnel would really get those drops in there!  Hmmmm.   Never done that.

Below, this morning’s Tucson sounding showing a bit of moisture at 550 mb or about 12,000 feet above Catalina (where the two heavy lines pinch together some).  The one on the right is the temperature and the one on the left, the dewpoint temperature.   This suggests their may well be some “flying saucer” clouds, Altocumulus lenticularis today, one that hover in place while often expanding and shrinking in minutes as the incoming air moistens and dries.  There are also indications for clouds at Cirrus levels, above 300 mb or 30,000 feet, and down around the tops of the Catalina Mountains; those would be Cumulus fractus, humilis, then later fattening up to mediocris as afternoon and evening wear on.  They will be marginal for producing ice during the day (which would mean virga), but, if the model is correct, they would deepen upward farther so that ice does form in them (tops colder than -10 C or so) and cluster into groups with appreciable virga and some rain overnight, probably looking more like Stratocumulus, a sky-covering layer  by morning.

You can also perhaps see that the winds are pretty strong over us already.  Not much now, but as the sun heats the air at the ground, and that air rises, compensating downward motions occur as the air above takes the place of the air that is warmer and gets lofted.  So, as we usually see, the wind will be picking up drastically this morning as both that happens, and those stronger winds above us are “mixed downward” in turbulent blobs we see as gusts.   Also, that that Tonopah low pressure center strengthens as it passes by to the north.

You can follow the development of this “Tonopah low” now located, of course, near Tonopah as of 5 AM AST today, here with the University of Washington Huskies’ surface map loop.  This former Husky employee notes that the Washington Huskies had a great basketball and softball weekend.   Oh, also, the loop will update automatically.  Here is the NWS detail on wind and stuff today for Catalina.

 

“The answer”, as well as a lot of other things, will be “blowing in the wind” tomorrow

What did that mean, anyway, the “answer” is blowing in the wind”?  What a crazy thing to say!   What “answer”?  I never heard it.  Me?   I liked, “Everyone Knows Its Windy”,  by The Association.   Now there’s a song…and “everyone” will know its “windy” tomorrow afternoon just like they said back then.  Very accessible song.  But first this diversion/tirade.

So much for the “plethora” of storms foretold by our models some nine days ago.   It even appeared that Catalina could have a snow day yesterday or today.  Poof!  The Catalina snow day was moved to Boise, Idaho.  Imagine a week before the Tucson Rodeo, it was announced that it had been moved to Midland, Texas!  Well, the models need to shape up!  They’re just awful beyond a week or so, always indicating, it seems, a big storm here.  What have our weather scientists been doing all this time with all that government money they get year after year????  (hahahaha, sort of).  ((Just kidding guys, now that I don’t get any government money to study weather and clouds at the big university where we all know its hobby work and we’d do it for nothing but don’t tell anyone….))

OK, one of the many “storms” foretold in the model will pass over us tomorrow.  It won’t rain.  The jet stream in the middle of the atmosphere will be a hair too far north, and the lower moisture  needed for precip and circumscribed by it will be so close that we will likely see some Stratocumulus off to the NW-N shedding some virga or snow and maybe some small Cumulus here (Cumulus humilis).    Probably most interesting tomorrow, if there is enough moisture in the mid-levels, say around 2o,ooo feet or so, is for a couple of Altocumulus lenticularis clouds to form, those almond like clouds.  Those can be pretty cool, and sometimes cause people to call in about seeing a flying saucer.  Really, its happened.  But we’re smarter.  We know “a” Altocumulus lenticularis when we see one!  In case you forgot, here’s one near Ashland, Oregon:

The low pressure center with this system is going to be pretty intense as it deepens over southern Nevada and then scoots on across Utah tomorrow.  “Intense” means it will have a lot of isobars around its center, and lot of isobars means wind because the pressure on the outside of the low is so much different (higher) than at its center.  I guess that is something; it will feel like a storm is coming, and the relative humidity will go up after the front passes.

 

The End.

 

 

 

 

The Great Divide…

in models.   Could be called,  “delta models.”  Below, nice pleasant weather, nothing much going on or threatening or an imminent storm, whichever you like from last night’s crunching of global data from two great computer models.  The first from our own US output , and the second from  Canada for the same time and day, this coming Sunday afternoon at 5PM AST, February 26th!

Trough along the West Coast(1)?  Or not (2)  Look at the giant trough protruding southward in that Canadian model!  I really don’t know which one will verify, and so I think I will go look at some flowers until this goes conundrum goes away.

As we all know, “the truth is out there.”  But where?  Fingers crossed for Canadian “solution.”

The End




Dark clouds but no rain yesterday. What happened?

Quick answer:  1) drops too small to coalesce and form ones bigger ones ; 2) no ice in ’em, for the most part.

Read below if you want a LONG discussion about yesterday; dull photos way below

Let’s talk about it, though probably more than you want to.  You’re probably a little down because it didn’t rain yesterday, hour and hour though it looked like it should, except for a couple of “sprinkles-its-not-drizzle” drops.    You probably had to use your headlights in the middle of the day like people in Seattle do.    It began to clear up some, gradually, in the afternoon. Here are a few of scenes below, beginning with the morning overcast, with the last two shots between 4 and 5 PM AST as the clearing was underway.

So, what kind of clouds are they?  Well, Stratocumulus in the first shot, in the second shot a higher layer of Altocumulus or water-topped Altostratus1 is underlain by Stratocumulus and Cumulus clouds  (when the bases are more isolated, we call them “Cumulus”;  when they are more connected together, we hedge the name toward “Stratocumulus”.)

The third shot, showing Stratocumulus looks particularly ominous, probably the darkest part of the daytime was here around noon AST.  A shot toward the mountains next shows the underlying Stratocumulus and Cumlus below the higher layer of Altocumulus/Altostratus.  These clouds can’t be “nimbo” this or “nimbo” that because there is no rain to speak of falling from them.  (“Nimbus” means rain in Latin.)  Note the good visibility under all of the clouds; no precip there.

Finally, with the breakup of the overcast, shown in the last two shots, we can get an idea of the thickness of the lower clouds, at least at that point, about 2,000 to 3,000 feet at most.  Also in those last shots you will notice that the higher layer has moved away or dissipated, and with a bit more heating, the clouds are tending more toward Cumulus rather than Stratocumulus.

The higher layer, located at Altocumulus level, about 12,000 feet above ground level, was actually the cloud layer producing the sprinkles, and was a key player in how dark it was; two layers, naturally, stacked on top of each other, will make it darker looking than just one, especially, in this case, when they are both pretty shallow.   And with a top at about -18 C, you can almost be assured that the top was composed of mostly droplets, not ice crystals.   A droplet cloud reflects much more sunlight back into space than ice crystal clouds like Cirrus and Cirrostratus.

Anyone still reading?  I’m doing my best here…

That last photo demonstrates that in spite of having a little rain overnight, and even during the day, there was a lot of haze/smog in the air.  It wasn’t washed out by rain.  And, the more clouds get bunged up with aerosol particles on which drops can form on,   the higher the concentrations of cloud droplets are in them, and the smaller they are as a result.   Smaller drops cause more sunlight to be reflected back into space, and when that happens, the bases look darker.  In Seattle, in our airborne studies, it was usually the case to have darker based clouds downwind of the city, and light gray clouds near the coast and offshore, even when both cloud layers were about the same depth.  However, there are natural sources, like volcanoes that can also affect clouds this way.   For example, “VOG” (volcanic smog) in Hawaii darkens clouds there because VOG has particles that can form drops in clouds.  I seen it myself and I know a dark, polluted cloud when I see one!

What happens when you get smaller drops in clouds, as smog produces in them?  It makes it harder for something to fall out the bottom in two ways.

First, in smog filled shallow clouds, drops don’t get big enough to collide and stick together to form larger drops (something that happens when they get to 30-40 microns in diameter (about a third of a human hair in width).  But, even in the event that could have happened yesterday, drops got that large, the result would have been only TRUE DRIZZLE, fine, close-together drops that go under your umbrella if there is a breeze of any kind.  Very tough on people who bicycle and wear glasses.

The more important key to not raining clouds, was that the clouds did not have, IN GENERAL, cold enough tops to form ice crystals.  The lower ones seem to have topped out around -5 to -7 C (23-20 F),  temperatures at which smoggy clouds with itty bitty drops cannot produce ice.  

The higher layer, seen in the second and fourth shots, was just cold enough, about -18 or so at top from the morning TUS sounding, to form a few ice crystals.  Also, being higher, it was probably not impacted as much by smog.

Quitting here, brain exhausted.  Hope this is somewhat comprehensible.

The End

1The smoothness of that higher layer is due to ice crystals falling out the bottom, obscuring an Altocumulus-like cloud from which they are originating.  Sometimes this has been called the “upside down” storm because the top is liquid like Altocumulus clouds where it is COLDEST, but underneath is all the ice, where the temperatures are higher.  (Man, this is getting way too complicated to comprehend!)

0.03 inches! Not as much as expected!

Want to keep the excitement level up…after all, it is raining somewhere near by…  Besides, if you’re excited, it will sound like more happened than really did.  (Another ploy is to report large amounts of rain somewhere else:   “An Avra Valley location got 0.39 inches late yesterday and last night.”  Really did.)

http://159.233.69.3/temp/pptreport.txt

Well, at least this rambling low “below” us in Mexico is not a total “gutter ball.”  It was looking at little grim for rain last evening with all the stars out.   Here is a loop of that low’s drift, with obs and satellite imagery on a 500 millibar map from my former “home” Department at the University of Washington:

http://www.atmos.washington.edu/~ovens/loops/wxloop.cgi?sat_500_full+9

You will see here that a blob of deep clouds is sneaking around in “back” of us and will likely deliver an odd fall of rain from the northeast as the low scoots off to Texas.   The models, in all their wisdom,  think the rain in those sneaky clouds can get over the Cat Mountains but to the east of us here in Catalina.  Don’t expect a lot, then, maybe just a hundredth or two if we are lucky this morning before those clouds starting thinning and moving off.  Still, it would be something.  Rain and snow threats are still in the model outputs (last night’s 5 PM AST one) in the days ahead for us, but have diminished  in magnitude; become more marginal in later runs, dammitall.  Hence,  this font size to reflect that.

Cloud report

Yesterday was one of the great days of clouds we have here so often, so pretty with all that snow coming down out of such little wispy clouds.  Here are some scenes, beginning with the momentary underlighting of  Altocumulus clouds shedding long virga trails.  In the second shot, I will no doubt have to admonish people again that to see what I saw, you must hold your computer monitor over your head. This was a long fiber of virga (snow), like those shown in the first photo, but was overhead.  So nice!

Cloud tops of these little clouds, those flat flakes at the top of the virga (sometimes called, “generating cells”, source regions for all that ice, by my reading of yesterday’s Tucson sounding,  were about -25 C (-13 F) at about 15,000 feet above the ground here.  These are low temperatures for us at that level, BTW.

The rest of the day was generally a joy, too, with terrific examples of glaciating (turning completely to ice) Altocumulus castellanus clouds (next shot).  Those whitish turrets in the foreground above the bush have glaciated, while the others are still mostly liquid water clouds, on their way to becoming icy, and cirrus-like.  This glaciation has just happened and you can infer that because the snow has not yet fallen from the bottoms of those clouds above the bush.  If you really look hard you can see the telltale filaments, fibers, stranding in those clouds, too.

A really nice example of “Ac cas”, turreted middle-level clouds, are those whitish clouds in the distance toward Kit Peak.  That next shot is of an Altocumulus turret long after it has glaciated with only a ghost of its former height shown protruding above a long, fibrous, icy trail.  There may have been other smaller turrets as well.

What was happening here is that the air just below these Altocumulus clouds, was only moist for a short distance, and then became extremely dry.  So, initiatlly, the ice that fell out of these clouds may have grown in size, but then when they starting falling into the dry layer, began evaporating rapidly.  As they did, the fallspeeds of the crystals went down to practically nothing and so, being something like diamond dust snow, seemed to float horizontally in the air.  And as they do this at these small crystals sizes, they lose the stranding become something akin to a fog of ice crystals that gradually disperse from the parent clouds.   Sometimes layers of Cirrostratus clouds, or large patches of thick Cirrus (spissatus variety) form in this way.  An example of ice clouds having formed like that yesterday in shown in the next shot.

Finally, just some shots of some pretty clouds, the next (supercooled) Altocumulus perlucidus (tending toward castellanus) and NOT showing any ice, and then just more shots of those little snowstorms in the sky.

The End, finally!