Definitions – Page 87

When the jet goes by, the clouds, lower ones, roll in

And that’s pretty much what happened yesterday. Here are some maps showing what happened as the jet stream in the middle troposphere (500 millibars or about 18,000 feet above sea level) went overhead while deploying to the east and south of us. The sky change was pretty dramatic as you may have noticed.

First, how the forecast model had it timed, then the sky pictures as it was happening. These panels, from IPS Meteostar, are for 2 PM, 5 PM and 8 PM AST (these panels look almost identical, but believe me, that reddish area, indicating the strongest winds, is shifting eastward over southern Arizona!) By 8 PM AST, the jet is completely past us (third panel).

The last panel, from the University of Washington, is the actual observations and “contour” map for 500 mb at 5 PM AST yesterday, that time when the sounding balloons (“rawinsondes”) went up. That flag and four and half barbs at Tucson tell us that the wind was over 100 mph at 18000 feet above sea level over us at that time, likely the heart of the jet at 500 mb. Its pretty unusual to see winds that strong so low.

You can also see in that contour map with satellite images of clouds that the clouds pretty much end south of that wind maximum at Tucson. At the same time, you can also see clouds puddled around inside the low in northern Arizona, encircled by a jet stream. This sight, no clouds or just high and middle clouds, on the outside of the jet core, and low clouds with precipitation, is a common occurrence in the Southwest into the southern Rockies. Scattered light snow showers were common in northern Arizona yesterday. It is virtually required before any precip occurs in SW in the wintertime, that you have to be circumscribed (“inside”) the 500 mb jet. BTW, this “rule” does not hold in coastal regions, such as southern California, or very far east of the front range of the Rockies, or in the summer months, of course. But its pretty solid here storm after storm.

And, of course#2, the sophisticated models of today know all about this “rule”, incorporating it in their outputs, and so we weatherfolk don’t really need to look for where the jet max is anymore like we did in the olden days of forecasting. Still, its simplicity is appealing.

On some occasions, such as yesterday, when only brief virga accompanied those lower clouds, it is a “necessary” condition for rain here, but not always “sufficient.” It was just too dry, even with this low’s little puddles of lower clouds filling its center.

The cloud sequence: 1) 1:38 PM: “nice weather we’re having.” 2) 2:18 PM: wha’ happened? Yesterday afternoon’s band of clouds accompanied the jet core passage overhead. Cool, and it got even cooler. Was hoping for a sprinkle, but didn’t get it. There was a brief radar echo north of Catalina about this time. That was it!

Since we’re still inside this jet/low this morning, there’ll be some lower clouds, Cumulus here and their, likely with a little ice, but too high and too sparse to have rain at the ground. Most of the dust should be gone now, so a great looking day is ahead!

The weather farther ahead? Some model fiction below, for March 19th. Nice scoop jet rises up into southern AZ after scooping water out of the Pacific off California. Would be a nice rain, if real.

Yesterday’s clouds, dust, and smoke; virga ahead

It was zero visibility in Parhrump, Nevada, yesterday afternoon with wind gusts to 85 mph, as the cold front was about to crash on by. I guess we were lucky to only have 40-50 mph puffs of wind here in Catalinaland overnight, and not so much dust (yet). A sharp, but dry cold front is bearing down on us, but the low center that was so intense yesterday over Nevada, then moved across Utah, has faded trying to move through the Rockies. This means that the winds will be much less than yesterday.

Does that mean no dust around Catalina today? Nope. Those strong winds in Nevada and western Arizona yesterday raised a lot of fine (as in tiny) dust particles that are likely to be suspended for a day or two, and so we’ll likely see dusty skies today, without so much wind anyway.

We had some nice Altocumulus/Cirrocumulus lenticular clouds in the afternoon yesterday. I wonder if you saw them? They weren’t around for long. Here’s what they looked like.

The last shot is of a cigar-shaped flying saucer with multicolored lights, OR, a Cirrocumulus lenticularis showing some slight iridescence (which are those rainbow colors near the edges of the cloud due to diffraction). You have to look very hard to detect coloration in this cloud shot, but its there. Diffraction is the bending of sun’s white light as it passes around the tiny (micron-sized) drops in the cloud and that leads to a separation of the white light into its components of reddish, greenish, blueish colors.

Take yer choice on what was photographed, but it is true that clouds such as lenticulars have been reported as flying saucers that “hover” then disappear. This cloud was completely gone in one to two minutes after this photo AND was stationary, as lenticulars are in the face of strong winds aloft and at the ground, which also influences the observer’s reports of unexplained “hovering.” This little cloud had been much larger ten minutes before reaching this size.

You can probably understand why such reporting might happen when you look at how smooth this little lenticular was. And sometimes, when nearer the sun’s position, the colors caused by diffraction are quite vivid.

Wildfire smoke

Also, in the late afternoon some smoke from the Nogales wildfire headed our way. It gave a great example of what young smoke looks like, that is, smoke recently emitted from a fire nearby. Its always got lots of gradations of the smoke in it because it hasn’t been around long enough for turbulence to mix out the smoke into a homogenous layer. This happens when smoke has been around for days and days and has traveled thousands of miles, and so its one way of telling that a smoke layer has come from a long distance.

Sometimes high, smooth, long-range transport smoke layers can be mistaken for Cirrostratus, hold yer hat, “nebulosus”, a completely smooth ice cloud without much internal detail. Below, the smoke from the Nogales area as it headed northward toward Catalina.

Rain possible?

It seems as dry as this system is, about all we can hope for is a trace.

It does appear that there will be enough moisture by tonight and for a couple of days as this cold air over us hangs around that we will see high-based (that is, probably based at or above the top of Mt. Lemmon) Cumulus and Stratocumulus clouds, and with the low temperatures aloft, ice should be able to form in them–which as you know, means virga, snow falling out and melting on the way down.

However, it would appear that only sprinkles are possible at ground level here in Catalina.

What to do?

You won’t want to miss entering the fact that a sprinkle occurred in your weather journal, one that might only last a minute or two, and so its best if you keep, say, your car parked outside where a layer of dust can accumulate, and then, when the rain drops fall, they will leave impressions in the dust.

The full moon of last evening, FYI.

Factoid: it is thought that the moon was originally part of the earth, the result of a gigantic (!!!) impact that sent part of the earth out into space which then became our moon. This theory would explain the synchronization of the moon’s face with the earth, that is, having the same face toward the earth. Hmmm. Hope we don’t have another one of those soon. Two moons would be mind boggling.

Cirrus, maybe some lenticulars, and dust ahead

In case you missed it, the thin layers of Altocumulus clouds provided a bit of a sunset “bloom” around 6:30 PM AST yesterday. Here’s what yesterday looked like, and I am doing this because I have a strong feeling some of you like to live in the past, like I do when I think about my best sports days in high school and JC R’s bat, and maybe a coupla others after that, so that’s why I am reprising yesterday below):

Here’s what we are looking at, in order of their appearance: 1) encroaching Cirrus (its not a cloud name, its what it was doing), 2) later, the Cirrus thickening (usually downward) into a nice example of Altostratus, a cloud normally composed of only ice crystals and snowflakcs, 3) Altocumulus perlucidus translucidus (honey-comb pattern, quite thin), with traces of ice falling out if you look VERY carefully, and 4) and 5), the Altocumulus as it was briefly (you only had a few minutes) underlit by the distant setting sun (its 93, 000, 000 miles away).

Moving on to the future, such as the rest of today

Its great, weather people can really do that, look to the future and say things that will actually happen with a great degree of confidence, like for the rest of today. (HELL, an economist can’t even predict what will happen in the next few hours!)

What will happen in the hours ahead? Cirrus clouds, patchy ones here and there, and a good chance of some Altocumulus or Cirrocumulus lenticular clouds as the jet stream powers its way down here, shooting from the southwest over us by late in the day. Sometimes, and I have predicted this before without a lot of success, you get these tremendously fine grained clouds (Cirrocumulus) that suddenly pop out of the blue overhead. There’s an awfully good chance of seeing those today, too, with the strengthening winds aloft. Of course, I’ll be watching for you if you miss them, and will replay anything “exciting” tomorrow.

Also, as the low in southern Nevada strengthens tremendously during the day, the winds will pick up as you all likely know by now, and the blue sky will start to wash out in a brownish dust haze. Twin Peaks may not be visible from Catalina late in the afternoon due to dust. You can track the development of that low here, from the University of Washington. Right this moment, 5:50 AM, there is not much there, so a lot of the development excitement in southern Nevada is ahead. The NWS, Tucson is quite excited about all the things that might happen, as you will see here!

Enjoy and interesting day!

The End

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.

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.

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¹Sorry, 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