Stratocumulus clouds – Page 9

Rainy days and Saturdays

Nice sunset yesterday….as some Stratocumulus spread over the sky underneath a pesky Cirrus cloud cover, clouds that announced the beginning of our next rain spell, now underway.

Light rain is falling this morning at 4:07 AM, and has been for hours, amounting to 0.01 inches. However, some places in Pima Land have gotten much nicer rains, around a third of an inch in the Cat Mountains overnight, for example; check here.

Progress of the real monsoon, since June 1st, can be checked back there at the beginning of this sentence. The coastal state of Karnataka has an average rainfall of about 70 inches since June 1st, a below normal amount, believe it or not. However, being a statewide average, that 70 inches doesn’t reflect the hill stations in the western Ghats, surely to have about twice that amount.

Now, as a further aside, Karnataka, Kerala, two Indian west coastal states would be a great place to go for a vacation now! There you could REALLY absorb a REAL monsoon, where passing rains, heavy, pounding, thick with drops, visibility down to less than a mile, go on hour after hour with brief interruptions. Its really pretty amazing and worth experiencing, at least once.

But, not much lightning there, like we have, because the rain develops mainly through a process not requiring ice, much like the rains in Hawaii where lightning is also rare. The rain develops largely through the collisions of drops, ones that stick together after they collide, and get bigger on the way down through the cloud, sometimes called the “warm rain process” because ice is not involved, and that causes most of the rain in that Indian coastal region. Cloud bases are right on the deck, and are typically 20-25 deg C, very, very warm.

In contrast, to continue a pedantic stream, “warm rain” is rare here in Arizony because cloud bases are relatively cool (less than 10 deg C in the summer as a rule), and droplet concentration are moderate to high (hundreds per cc). Higher cloud droplet concentrations make it harder to grow cloud droplets big enough to collide and stick together inside our clouds.

But, we do get that kind of rain, “warm rain” here once in a great while in Arizona as part of the rain that forms in our Cumulonimbus clouds when their bottoms are especially warm, higher than 10 deg C. Seems to happen about once or twice a summer in my experience so far.

What’s ahead?

Now that afternoon and evening rains around the area are back for the foreseeable future (5 days), what’s way ahead, beyond the foreseeable future?

There, as you know, when we start thinking about beyond the foreseeable future we start thinking about spaghetti! What do those crazy northern hemisphere-wide plots produced by NOAA with their dizzying numbers of lines mean for us here in Arizona?

First, I present a map of the 500 millibar contours as produced in the Haight-Asbury hippie district by San Francisco State–I mention this because the lines on this 500 mb map look a little nervous and maybe it has something to do with that map origin, being from a cultural area whose norms are “anomalous.” I have pointed out on this map, “Our Big Fat Anticyclone”, one whose position is critical for decent summer rains here. In this map, as you can see, its not really OUR “BFA”, but rather belongs to Amarillo, TX, as of last evening.

Nevertheless, it is well positioned to fan humid air from the southeast into Arizona, as is happening now. Remember, the circulation around a big fat anticyclone is clockwise. When it sits on top of us, things are not so good; upper level temperatures are high, humidities are low up there, stifling convection and preventing tall Cumulus clouds.

But when the high is away on holiday, temperatures are lower above us, its more humid up there, and those factors allow for deep convection; huge Cumulonimbus clouds. It only takes a few degrees difference to go from those dry days we just had with their Cumulus pancakus, to the kinds of days ahead for us now, where clouds stand tall!

Continuing, finally, Here’s is today’s plot for 15 days from now, the afternoon of August 11th, based on global data taken at 5 PM AST yesterday. What do you see? You see an arrow pointing to something of a void in all the “spaghetti.” That void represents the most likely position of our BFA some two weeks from now, and that position is pretty darn good for summer rains here. And it is in that region, to the north of us, almost the whole time from now!

So, based on this “most likely” position, one would venture that the rich summer rain season we have had thus far, will continue to be active. Of course, this doesn’t mean rain everyday, but that breaks will likely be short through almost the first two weeks of August.

Can you imagine how tall those desert grasses and weeds will be by then if this is the case?

The last couple of photos document our fabulous re-greening now in progress. If you haven’t been out in the desert, you should get out there and experience this wonderful event. Doesn’t happen every year, as we know!

Early to rise

SONY DSC — 9:42 AM: Small Cumulus clouds first appeared over the Catalinas within a half hour of this shot.

These small fluffs of Cumulus clouds above Ms. Mt. Sara Lemmon, were the first indications that something good, and very different from the previous two days was going to happen yesterday. These clouds appeared no less than 4 h earlier in the day (between 9 and 10 AM yesterday) than those first Cumulus on top of the Catalinas on the previous two days.

The correct emotional response due to this early rising for cloud maven juniors and doscents out there should have been excitement and anticipation; that some big boys with long names (Cumulonimbus capillatus incus) were likely going to be around later in the afternoon and evening hours. No weather maps needed! See AZ Star for confirmation.

While we didn’t get a big dump right here in Catalina, we did at least get a dust-coagulating 0.02 inches. Here are the totals ending at 24 h from around the region from the Pima County Alert gages. The most hereabouts was at the Santa Cruz River at Ina Road with 0.59 inches, with that storm shown in the photo at 4:25 PM below.

Today, with dewpoints once again being in the upper 50s, it should be the case that we see these early precursor clouds on top of Mt. Lemmon, and they will once again lead to the conclusion of a satisfying day of thunder and intense rainshafts, driven by 100 F plus temperatures. It peaked at 106 F here yesterday in Catalina, and it was fairly cloudy when that temperature was recorded! Pretty remarkable.

Here’s your NWS computer generated forecast for Catalina, foretelling similar temperatures for today.

Here are some later shots of those great clouds, and if you want the whole nine yards, go to the U of A time lapse movie here. There’s a lot of rotation at the bottom of some clouds 1:03 before the movie finishes, and an indication of a rope-like funnel cloud, not too surprising given the instability of yesterday.

DSCN1915 — 4:23 PM. Eventually of those Cumulus congestus clouds reached ice-forming heights and produced our little 2 hundredths shower. By the time it reached Saddlebrooke, it had a visible shaft.

DSCN1919 — 4:25 PM: While our little shower passed by, Marana and vicinity were getting the real thing in dumps of more than half an inch.

DSCN1924 — 5:18 PM. Ditto to the NW where heavy rainshafts in this complex created a “haboob” that affected Casa Grande.

Maybe today, with plenty of clouds and heat, it will be our day to get the big dump and wash the dust off our desert plants.

The End.

Clouds of yore, well, those on Thursday, April 26th

Kind of got distracted with chores after the big trip to NC and didn’t get to this until today… If you can remember as far back as April 26th, we had a “FROPA” (“frontal passage” in weatherspeak) that day. The U of A weather model indicated beforehand that the bases of the clouds last Thursday would lower to the tops of Samaniego Ridge.

Well they did, though it seemed in doubt for a time, and occurred a bit later than the model had predicted.

Also, a few drops came down here late in the morning; more precip was visible to the north of us and that was reflected in the NCAR precip estimate for Arizona the following morning, an estimate that suggested the heaviest rains were up to half an inch just 150 miles away.

Here are a few of last Thursday’s clouds with some commentary.

These clouds came in two separate segments, the first batch were at Altocumulus levels, some 12,000 feet above the ground according to the TUS balloon sounding that morning at 5 AM AST. Those were the clouds that produced the sprinkles around 5:30 AM. Poor snowflakes melting into drops had to fall such a long way!

After a brief clearing, a surge of lower Altocumulus and Stratocumulus came in. For a time, they looked awful threatening, and appreciable rain could be seen falling from them to the north. They produced a few sprinkles here in the late morning and early afternoon about the time the clouds had lowered (as predicted by the UA model, to the tops of Samaniego Ridge to the east).

Why didn’t they rain more?

The answer, as always here, is that the tops were much shallower, and therefore warmer, than those early Altocumulus clouds sporting considerable ice at times. You can be sure that those Stratocumulus clouds over us had tops warmer than -10 C (14 F), a general threshold for ice formation around these here parts. (Over the oceans, where the drops inside the clouds are larger, the threshold temperature for ice formation is higher.)

Just to the north of us, where rain was occurring, you can be sure that the tops sloped upward in that direction, becoming colder than -10 C.

That second batch of lower clouds looked dark and threatening, but lots of times with lower clouds its because they have higher concentrations of drops in them, not because they’re especially thick as you might guess at first. The droplet concentrations in those dark Stratocumulus might have been twice as high as in those early higher, Altocumulus clouds.

Drops in clouds with higher droplet concentrations, say due to smog, reflect more of the sun’s light off the top. That makes them darker on the bottom, and because they are then also harder to get precip out of, they last longer.

This is a real problem, BTW, for climate models, since longer lasting clouds reflect more light back into space and in that sense, and help counter the global warming expected from trace gases like CO2. But, would you rather have ugly clouds and smog infested skies and a cooler planet, or clean skies and clouds and a warmer planet?

The weather ahead

No rain in sight. But a big heat wave, probably temps around 100 F now looming toward mid-may. May is our driest month, BTW, averaging only a quarter of an inch.

Rain and cold foretold for Catalina on Saturday as big, long-foretold storm bops Cal then moves on to AZ

Things are falling into place. Remember the spaghetti from a week or more ago, in which it was clear, or at least at attempt was made to explain to both readers of this blog, that a large trough was almost certainly going to be along the Cal coast? We intuited that from the lack of spread in some contours in that “spaghetti” plot along the West Coast some week or more in advance.

Well, that trough is truly turing out to be a behemoth, a gigantosaurus for April. The people of California are going to be very excited today and tomorrow about cold, showery weather, mountains of snowfall in the mountains, maybe a funnel cloud or two in the Sac or San Joaquin Valleys. Here is that trough as shown on today’s 5 AM AST 500 millibar map from the U of WA weather department, the one prophesized with high confidence so long ago:

However, for many days after that, the models did not think the rain in Cal was going to get here. Of course, still being in the cool season, our rain is nearly all dependent on whether the jet stream in the middle levels (500 millibars or about 18,000 feet above sea level) is able to be over or especially, south of us here in Catalina.

But lately, in the forecasts, been shifting the jet southward and rain has started to show up in two or more recent model runs, always a good thing. You may also remember that in our spaghetti plots back a week ago, it was not clear in the models where the Cal trough was going to go after it bashed the West Coast. Hence, while things were clear for Cal (actually, they were going to be cloudy and rainy), they weren’t so clear for here until lately.

From the U of WA, this for Saturday morning (colored splotches denote where the model thinks precip has fallen in the prior 3 h); below, the jet stream at 500 mb from IPS Meteostar for the same time.

Yesterday’s clouds

In case you missed them…. Cumulus and Stratocumulus, punctuated with a splash of Cirrus fibratus undulatus (Cirrus with rolls, showing something akin to swells in the ocean in the atmosphere). The wind at Cirrus level in that shot is blowing from left to right. No ice falling out in Cu and Sc; too warm at cloud top. Only about -5 C (23 F) or warmer.

The End.

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.

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.

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!)

Sprinkles! (coded as “RW- -” if you are keeping a weather diary!) (Its not drizzle!)

Pretty excited up there, as usual.

The Cumulus and Stratocumulus clouds began filling in yesterday, and some shed ice/snow virga in the late afternoon. With that a few drops of rain (melted snow, of course) plopped down on Catalina. In case you missed those drops, here they are.

Also, here are a few shots of those clouds, ones based about 7,000 feet above us, judging from their height above Mt. Sara Lemmon.

Note the trails of virga dropping out of Stratocumulus clouds near and over the Cat Mountains in shots 3 and 4. That was the “worst” of our “storm” right then when the clouds got their deepest, which wasn’t all that deep, maybe 3,000 feet or 1 km.

By now, too, you will know instantly that the top temperatures of those clouds, to be able to produce ice, were lower than -10 C (14 F). This kind of knowledge about local clouds and ice, is also a great “ice breaker” at parties and barbecues. In fact, the TUS sounding suggests that the general top was about -12 to -13 C, with likely momentary tops protruding to -15 C or so. This would suggest marginal ice formation in clouds with bases as cold as ours were, about -7 to -8 C (about 18 F). (Strangely Believe It: warmer cloud bases with the same top temperatures as we had yesterday, leads to more ice formation, and precip.)

Below the photos is the mid-level weather map for the time the sprinkles occurred from the University of Washington. Since the wind follows the green contours on this map, you can see two things. The wind maximum at this level (500 millibars) is south of us over northern Mexico, and that the wind was on the verge of shifting to the WNW above us at map time (5 PM AST yesterday). That wind shift line is referred to as a trough, and at, and ahead of the wind shift line, clouds and precip are stimulated, while behind it, the air gets drier and clouds are mashed down or disappear. You could even see that happening to the west of us yesterday afternoon while the clouds were heavy and precipitating over the Catalinas. Those clouds over the mountains, too began to whither, and the virga ended, not JUST because it was heading toward evening and getting cooler, but also because of that trough was passing to the east at that time and the drier, descending air was moving in over us.

In this map, you will also see the much stronger trough over northern California, one that is racing toward us and will bring rain as early as tomorrow morning! Yay! However, the U of AZ massive Beowulf Weather Calculating Computer Cluster foretells only about a tenth of an inch from this next storm (here). Boo! I will suggest that might be a little on the light side, but that’s because I am biased and strongly want more rain than a tenth from this new storm; I’ll venture 0.25 inches or so here in Catalinaland by Wednesday morning.

More storms after this next one? Oh, yeah!

The End

A Stratocumulus Monday

Yesterday gave us “Catalonians” the perfect example of Stratocumulus clouds. But why didn’t it rain from those dark clouds, save a few drops, maybe even a brief drizzle episode that mostly moved across Saddlebrooke around 9 AM?

Those Stratocumulus clouds were GENERALLY not cold enough at cloud top to have ice crystals form in them. There were some very light showers, mostly east of us during the day, and THOSE clouds got cold enough at cloud top to have ice form in them.

How cold does a cloud top need to be in Arizona for ice to form in it?

Around 15 F (-10 C).

Here’s the TUS 5 AM AST sounding for yesterday from the Weather Cowboys at the University of Wyoming showing the tops are right around that (normal) ice-forming limit. Where the lines split apart is close to where the cloud tops are, and the temperature lines slant downward to the left.

You may have also noticed that the clouds got markedly shallower here after about 3 PM, noticeable in the U of A movie after 3:30 PM AST. That was also close to the time an upper level trough and the accompanying slight wind shift occurred. To the rear of the trough, there is always a piston of downward moving, drier air that’s going to squash cloud tops. By the evening TUS sounding, cloud tops were barely below freezing.

Some cloud shots from yesterday’s overcast:

The weather ahead

Still looking for rain here on the 22-23rd, HOWEVER, the last two model runs confined the rain to N of us! Not good.

Nor Cal rains/flooding episode begins overnight as a series of semi-tropical storms strike the coast.

Wish I could be there for surf and on the turf there, but I have my blog audience to think about. I don’t want to let both of them down by being gone for the 10 days of this great storm series, exploring the rain intensities in the coastal ranges of Cal. Oh, well.

Still think total rains in the best coastal mountain spots over the next ten days will be 30 inches or more, actually not terribly unusual in the King Range and similarly exposed sites.

Twice as nice; 0.53 inches in Catalina (0.58 inches as of 6:39 AM AST)

What a superb rain that was last night. It just kept coming until finally we piled up an astounding-to-me 0.53 inches by 4 AM this morning. The regional rain reports from around Tucson can be found here. As you will see, the upper regions of the Catalina Mountains got around an inch (1.22 inches at CDO wash at Coronado Camp now). Mt. Lemmon probably got a little more, but the record says “0.00” due to snow at that elevation. This is a substantial boost for our emerging spring desert vegetation after our four week drought. This is so much better than that near rainless January of last year! Looking at some of the statewide precip reports, it looks like the Catalina area and the Cat Mountains got more than anywhere else. Lucky us.

If you would like to relive yesterday, at least in clouds, go here to the U of AZ time lapse. One of the things you will see later in the day are Altocumulus lenticularis clouds over the Catalinas. You will see their upwind edges spurt upwind (seem to go the “wrong way”, against the wind) as the lifted air got more moist, one of the tricks that these clouds can pull. You will see quite a panoply of clouds in this movie, from Stratocumulus, Altocumulus, Altostratus (dead gray and smooth higher layer), Nimbostratus (when the rains come) along with some mammatus formations. Hmmmph. There’s that “m-word” again, the one I used so many times yesterday. Wonder what’s going on?

“But wait, there’s more!”

If you call now (well, actually if you continue reading) you’ll find that a few more hundredths of rain are possible this morning before about 8 AM AST, AND, (We interrupt this blog for an important message: “hey”, just started raining again now at 5:03 AM! Yay!)

all of the model runs are indicating rain again on the 22-23rd timeframe; even the “pernicious” 00 Z run from the 5 PM AST global data. (I have questioned that output of late, rationally or irrationally, because it kept drying the State of Arizona out whilst the model runs before and after that time, foresaw precip in spades in the State.

Here is a sample of the IPS Meteostar renderings of what happens in our rain window of the 22-23rd according to our latest model run, one from 11 PM AST data. Note green areas of precip in the 6 h ending at 5 AM AST, Jan 23rd. This is pretty satisfying since another good rain will keep us on track for a great spring bloom.

On other fronts…

While I could go on to talk about all sorts of things due to the ambiguity of the subtitle phrasing above, I will actually only talk about weather fronts, not this or that.

The coming floods in northern Cal-Oregon still on track. Storms break through from the Pacific “under” the Bering Sea “blocking” high, one that diverts the potent Asian jet stream that comes into the Pacific into two branches, one of which is forced southeastward in the central Pacific where water temperatures are warm. (Just heard some rain on the roof again. What a nice sound that is!) The other branch goes deep into the Arctic and merges with the southern branch in the eastern Pacific after it turns southward over AK.

Those warmer storms, heavy with semi-tropical rain clouds, race to the West Coast once the southern jet breaks through the weakening southern part of the blocking high. And once that jet stream has broken through, its days before things change, so the duration of rain adds to the colossal totals certain to occur now. In a ten day span, beginning tomorrow, the peak totals in this event will likely exceed 30 inches of rain.

Here is the current weather map (5 AM AST today) from the University of Washington that illustrates the odd flow pattern developing now from the central Pacific to the western US. The block is developing from a ridge in the eastern Pacific now (evidenced by the lack of green contours in it) that extends from the tropics all the way to the Bering Sea! It will fracture in its southern portion tomorrow. It has overextended its “reach”, in a manner of speaking, at this point, and will fail just like a dam break and all those clouds to the west of it will flood eastward. Its a pretty exciting thing for us precipophiles.

Canadian behemoth

One particularly bruising storm, one the size of Asia practically, with “tentacles” from the Aleutian Islands to Minnesota, was shown to develop in this series of storms battering the West Coast in the European model run by Environment Canada based on last night’s data.

I show this output below because you RARELY see a low whose circulation is this big, at least one of the biggest I have ever seen, portrayed on a weather map (upper right panel). The map below showing this colossal low is valid for the evening of Jan. 21st. The entire West Coast would be battered by this bruiser.

The End.