What a day, Mr. and Mrs. Catalina, except for that last second “header”:
7:57 AM. Cirrocumulus with exceptionally fine granulation (left center). You might feel a little chop if you were flying in it, but it would be hardly anything. More chop, lower right, where you have something akin to ocean waves rolling along from left to right.
8:04 AM. Pretty Cirrus fibratus (strands are pretty straight in Ci fib).4:47 PM. Pretty Cu humilis and fractus scene near the S-Brooke population complex.5:05 PM. Cu hum and fractus over the Catalinas, Nice shadow bounds the mountains I thought.
The weather way ahead, 10 days and beyond; dreaming green pixels
Rain showing up around these parts beginning overnight on July 3rd-4th, kind of a normal time for a summer rain season onset. This from last evening’s global model crunch. Prior model runs have been dry, so it could be bogus, of course. But, its a hopeful sign. Rains every day after that in this run. Below, the titillating start as rendered by IPS MeteoStar:
Valid at 5 AM AST July 4th. Green areas show those ones where the model has calculated some rain in the prior 12 h.Valid at 5 PM AST July 8th. Raining all over Arizona by this time. How great would that be? Com’on model! Don’t let me down! A feel a really old song coming on about being let down.
Let’s look at some spaghetti and see if the “solution” above has any credibility at all:
Valid at 5 PM July 4th. Note gaps in red lines in Arizona and NM. Errorful mod runs (deliberately so, recall) are therefore pretty confident the necessary ridge of high pressure aloft WILL be centered just to the north of us at this time, extruding all the way from the central Atlantic. So, there is a fair amount of confidence from spaghetti that the summer rain season will start pretty much on time. What’s also supportive is the bulge in the jet stream to the north in southern Canada, as indicated by the bunching of those bluish lines. Pac NW looks cool and rainy with this pattern, BTW. You can enjoy more spaghetti here.
So, right or wrong, you heard it here first because I got up early; summer rain season looks to start on time.
In case you didn’t notice, there was a prolonged street of clouds emanating from possibly as far away as Kit Peak, or maybe just the Tucson Mountains. Lasted for a few hours.Happens only on days with relatively shallow clouds (cloud-topped boundary layer) with a little wind, meaning that the thermals from the surface heating ended up being capped by an inversion or other stable layer, and those thermals form clouds in some places. In this case, a long line of intermittent clouds formed from an initial air bump caused by those mountains far to the SW of us. CTBL is more often invoked as a term by cloud folks when the sky is much cloudier in low clouds than these shots from two days ago, such as when the sky is covered in Stratocumulus clouds.
These kinds of streets occur over the same places whenever a day like this comes along. Think of it, especially here in Arizona, as a row of shady air under which you might like to live compared to those areas on either side of this cloud “street.” In Seattle, where the “cloud topped boundary layer” is almost a daily occurrence, you want to avoid being under the cloud street, where it can block the sun, and instead find the clearer slots!
12:14 PM.1:07 PM.3:19 PM. Barely hanging on now, but still present. Dissipated within about a half hour of this shot.
TUS rawin for June 18th, 5 PM AST (launched about an hour and a half before that).
For those sharpies that day and logged in their cloud diaries that ice formed in those shallow Cumulus clouds, they will be a little chagrined by this TUS sounding. This sounding suggests the clouds around the balloon were topping at -8 C, too warm for ice formation in shallow Cu. Let us begin to explain this puzzle by presenting evidence of ice formation in those clouds on the 18th:
4:13 PM. Virga hangs down from Cu mediocris, maybe only a km thick toward Charouleau Gap. Lots of ice visible.
4:13 PM. Overhead view of likely ice vellum between Cumulus clouds. The clouds themselves may well have a few ice crystals, but too few to provide any visual indication except in the clearings between them. Ice crystals evaporate more slowly than liquid drops when encountering sub-saturated air between clouds, and so can be visible a bit longer if present between clouds in marginal situations like this. Confidence level that this little patch is ice and not just haze is about 70-80 percent.
Simple answer to our connundrum; due to lifting of the air as it approached and went over the Catalina Mountains, the tops of the clouds reached those temperature below -10 C where is begins to form. We would guess even closer to -15 C in that cloud in the distance beyond Charouleau Gap due to the amount of ice. Ice increases with decreasing cloud top temperature, but the temperature at which ice onsets can change on a daily basis; higher onset of ice temperatures on days in which the clouds have larger drops in their tops (a phenomenon originally reported by Ludlam in 1952, then re-discovered by Rangno and Hobbs (1988) who did not, at that time, know of the Ludlam finding, and thus, did not cite it. Pretty embarrassing, really. Was cited later in an update, however.
The weather way ahead
Seasonal rains beginning to show up in southern Arizona now on models beginning around the 4th of July as a big anti-cyclone parks itself over the Four Corners area in the latest model run from 11 PM AST last night. Very excellent run.
Began at 1:15 PM, ended at 1:40 PM. Then, a second round at 3:58 PM. Nothing more on tap today through June. Thought, too, since there’s been a lot of talk about the Southwest monsoon lately in the media, we’d check on that and see how its doing:
This as of June 15-17th (green lines, red lines are normal position. Things are not so good, seems to be running a week to two weeks behind schedule.
Hmmm. Not so well so far. Is this being impacted by the developing El Nino? Our summer rain season, more often than not, has been disappointing as well in El Nino summers. An El Nino is in formation as you likely know.
Your cloud day yesterday, in thumbnails:
A better way would be to go to our University of Arizona time lapse movie here.
5:55 AM. Now I didn’t mention yesterday because I didn’t want you to feel bad, but these crepuscular (aka, “crepsucular”) rays were due to a lot of smog in those clouds yesterday morning. Got mixed out as the day progressed. Likely, from tropical Mexico based on trajectories at cloud base level.5:55 AM. More smog and clouds, some virga. Ugh.6:18 AM. Could be called, I think, Altocumulus castellanus or Cumulus due to the large size of the elements. However, they are not Cumulus arising from warm air near the ground, but rather from the gentle lifting of the air over the Catalina Mountains.6:20 AM. One of the remarkably small, sprinkling clouds that passed over yesterday. To get rain to the ground from about 11, 000 feet there would have to have been graupel (small, soft hail) forming in those little guys. Single ice crystals, or fluffy flakes would never had made it all that way since they would have dried up. Think of how great it would have been for you to non-chalantly, in your morning walk with neighbors yesterday, to have dropped the bombshell that, “Must be hail, soft hail, up there in those clouds for rain to fall on us from so high up.” You can see your neighbors’ jaws dropping in disbelief at that point! But you would then be some kind cloud hero to them, never to be seen the same way again. You wouldn’t say anything more about it; you’d made your point, succinctly I might add, and they’d likely get bored hearing anymore about it. Its best to let them just think about it the rest of the day.
Afternoon…..
12:53 PM. Promising Cumulus congestus are forming over the Catalinas, some already spewing a little ice. Here, about 2 km thick, or something around 6,000-7,000 feet thick, tops already about -10 to -15 C.1:15 PM. Taken just after first thunder heard from this modest Cumulonimbus. Not much shafting yesterday at all, suggesting weak updrafts and modest condensed water in them. No cloud to ground strikes were observed, and the time between thunder was a few minutes, all adding up to marginal conditions for thunderstorms near us, anyway.1:15 PM. One of the signature shots for this website, added to the “cloud base” collection. Here, graupel strands are just barely dectable as they begin fall out.
1:37 PM. Just before the last thunder, this icy top to a cell approaching Mt. Lemmon. Since the transition to all or mostly ice has occurred, this Cumulonimbus would be termed a “calvus.” The outward transition to all ice happens very rapidly, just in a few minutes, kind of an exciting thing to see!1:37 PM. Here’s what the bottom of that top looked like. No major shaft yet, but there will be but out of view.4:02 PM. Second round of occasional thunder in progress. Nice to see a little rain on the Ridge (Samaniego).7:31 PM. After all the excitement, we were left with little rows of Altocumulus perlucidus to celebrate a great day of cloud scenery.
As the day rolled forward in time as they do pretty consistently, I was really happy for you having so many things to log in your cloud diary and maybe report to neighbors who might not have been so observant as you yesterday; the various types of clouds you saw, fun dust devils here and there spinning their way across Catalina, Cumulus clouds, a couple of which grew into Cumulonimbus clouds, and even produced a thunderstorm way over there in Safford. You could see that one from here, too. And there was a spectacular chances for you to test your ice-in-clouds acuity score.
Let’s go over yesterday’s clouds and make sure you got them right; but remember, don’t feel bad if you missed something. Cloud maven person will always understand and forgive those who might call a cloud by its wrong name. Believe or not, even CMP has done so1.
10:56 AM. Altocumulus lenticularis patches underlain by a tufts of Altocumulus castellanus.11:51 AM. Mostly Altocumulus castellanus and floccus (no firm base, just a tuft). CMP’s cloud chart points out that rain might follow in 6 to 196 h when this form of cloud is observed. It indicates strong instability at this cloud level.11:53 AM. Fun dust devil goes across Catalina. No jumping castles were harmed. CMP used to jump in dust devils when he was kid when they came across the school yard at playtime. Maybe you did, too.1:17 PM. Small Cumulus (humilis) begin erupting over the Catalinas. Portent: moderate.1:54 PM. Cumulus fractus over Saddlebrooke and points NW. Not much going on in the high mountains, either, (as would be seen by tops of Cumulonimbus clouds) suggesting a dividing line in the moist plume over us; drier to the north, more moist to the south.2:24 PM. “Wow!”, you thought, if I may interject one for you that you should have had yesterday viewing this cloud. The real look of our summer rain season (aka, “monsoon”), a tall, thin Cumulus congestus cloud.2:24 PM. And at the same time, a Cumulonimbus capillatus incus (icy anvil) has formed over there toward Safford! Now summer’s on! Safford reported a thunderstorm about this time.2:54 PM. We really haven’t had an Cloud Maven Junior (CMJ) ice IQ test in quite awhile, and so I thought would give you a little surprise quiz today in the following photographic sequence. Here we see, while not driving I might add, that would be crazy, to add that bit more, we see a protrusion from a Cumulus congestus cloud. Will it turn to ice? And if it did, when exactly did you know that?2:57 PM. Ice in the top tuft yet? You have 10 seconds to come up with an answer.2:59 PM. “You are so ice!” Cloud Maven Person got quite excited and has made a call for you, prematurely. See how the finer detail has started to disappear as the droplets evaporate and the slower evaporating ice (in much lower concentrations) begins to dominate the appearance of the little tuft. Compare the newer tuft on the right and its ruffled appearance to the little, detached tuft on the left. In the one of the right, the much higher concentrations of droplets still dominate providing all kinds of visual detail, though ice would undoubtedly be present inside it and about to take over.
3:04 PM. Secret’s out! The little tuft shows its ice. Poor guy has no droplets any more, is just a defunct ice cloud on its way to evapo-oblivion. Note icy fallout from the trunk of the original cloud now. And, you now know that those sharply outlined turrets in the center of the photo have a ton of ice in them, though droplets are also present (soon to be gone as in our icy little remnant to the left).
The End
No further weather ahead of any interest to a CMJ, anyway. Darn.
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1As a kid, I think I once called an Altostratus translucidus an “opacus.” It was pretty embarrassing.
Blobs of sprinkle clouds pummeled Catalina yesterday beginning soon after 12 Noon and ending only after 7 PM when an extraordinarily rare “Geo-Astro Meteo Conjunction” (GAMC) was observed due the conjunction of a rainbow, a moonrise exactly over Mt Lemmon, and the top of Mt. Lemmon itself visible through rain. The GAMC “trifecta” scene, is thought to occur only once every several hundred years. The duration of yesterday’s scene was about 3 minutes, the cloud with the rainbow having produced a sprinkle here just prior to the rare scene. Only more rare than the GAMC is a sunrise exactly over the crest of Mt. Lemmon with a rainbow in the direction of the sun.
Three sprinkle periods were recorded yesterday, the longest between 5:43 and 5:45 PM. The others occurred at 12:28-12:29 PM, and 7:26 to 7:27 PM. The rain brought June’s monthly total to a trace, ending the prospect of a completely rainless month.
No accidents were reported due to excited motorists reveling in the “rain” on their windshields, having attention diverted from driving. Local meteorologists explained that higher dewpoints than expected allowed a few drops to reach the ground instead of evaporating completely from the high-level virga that had been forecast earlier. The higher dewpoints allowed cloud bases from which the virga fell, to be 100 millibars, or about 4,000 feet, lower than computer models had predicted. The meteorologists blamed a lack of data far upwind of Catalina for the forecast gaffe.
Below, a rare GAMC, one that you will like not see in your lifetime if you did not see it yesterday:
7:28:26: A truly rare GMAC scene develops toward Mt. Lemmon (the subtle, rounded hump below the moon). This scene can only occur with the rain and sun in proper positions to produce an arc of a rainbow framing Mt. Lemmon, but the rain must be light enough so that neither the moon nor Mt. Lemmon are obscured in any way. Yours, today only, for $1,000,000.
Moving on…..yesterday’s clouds
6:33 AM. Pretty Altocumulus, fatter version of “perlucidus.” Didn’t look to be as interesting a day as it turned out to be. This layer was about 12,000 feet above the ground.12:38 PM. Some Cumulus begin forming underneath the sprinkle clouds (ice/virga visible on the bottoms of the Altocumulus clouds on the left–that made the bottom smooth.)1:17 PM. Gorgeous example of Altocumulus castellanus and floccu (no ice/virga).
5:30 PM. Cloud complex of the day, loaded with sprinkles, CMJs were predicting that sprinkles, and ONLY sprinkles, were about 5-10 min away.5:46 PM. Following the sprinkle, eyes should almost automatically turn to the east for a some rainbow eye candy.7:37 PM. The pretty cloud day closed out with a satisfying sunset.
The weather ahead
Today looks like it will be pretty much like yesterday, lots of mid-level clouds cold enough for virga, as you can see out there right now (just after sunrise), supplemented by afternoon Cumulus. Altogether another pretty day with reasonable temperatures held down by clouds and virga around. We’re on the edge of this mid-level moist plume coming up out of the Tropics, BTW. Rain is foretold by the quite wonderful U of AZ Beowulf Cluster calculator to only fall in the SE corner of the State today. This from last evening’s 11 PM AST data.
The later model runs have had potent Hurricane Crissy’s moist plume missing us to the east now, so don’t really want to talk about it. Winds in Cristina now 145 mph sustained as it rapidly intensified from yesterday’s 75 mph. Should mean good surf along the west coast of Mexico and a certain south-facing southern California beach haunt of CMP, called, “Zuma Beach”, where the acclaimed dramatic series, “Baywatch” was first filmed.
Looks pretty good…. Two completely different computer models show tropical moisture getting into Arizona in about 5-6 days a resulting preview of the summer rain season. You can find quite a bit of “green pixies” (areas of rain denoted by areas of green pixels) in Arizona here from IPS Meteostar’s rendition of our best model, the WRF-GFS. And, the Smoking Canadians have rain in our area in their model, too. This is going to be the best chance for measurable rain in Catalina since early April!
In the US model linked to above, you can also see the residual low pressure center from today’s Hurricane “Crissy” moving up the coast of Baja Cal in five days. Finally, could we have a month with above normal rain after not having one since November 2013 (or was it 2012?) Might happen, after all we deserve it. So, I will now predict that June will be above normal in rain in Catalina, AZ.
You can keep track of Crissy here. I will be tracking Crissy, that’s for sure.
Below, an example of rain (with drizzle) in case you’ve forgotten what it looks like in a research aircraft with laser beam imagery of all the stuff you’re flying through:
Rain (and drizzle drops) as seen by aircraft instrumentation, arranged in order of small to larger, left to right. The horizontal lines are just about a millimeter apart, so the biggest drops here, one that aren’t breaking up, are about two millimeters in diameter. Drizzle drops, as CMJs know, are those between 0.2 to 0.5 millimeters in diameter, so there are a lot of those. BTW, these were collected while the aircraft was flying at about 160 knots (80 meters per second). Pretty amazing you can image these drops as they go by so fast!
The discerning reader will want to know what spaghetti sez; what are the chances that the steering winds in the middle of the troposphere will steer Crissy toward us as it moves around off’n Mexico. Will those steering winds help Crissy’s moisture get into Arizona and over Catalina?
We seek help from spaghetti and, indeed, the spaghetti shown below is “supportive”, that is, it shows that the “planets are lining up” for rain here, as an astrologer might say, those people we look to for personal guidance in everyday matters; whose forecasts are so important no newspaper can go without them without causing an uproar on the part of their readers.
See writing on figure below for some additional weather interpretation.
Valid for 5 PM AST June 16th. Those red lines suggest that Crissy’s remains (RIP) might indeed be directed at eastern Arizona! Big trough for this time of year foretold along West Coast with high confidence, as indicated by “bunching lines”, perfect for drawing tropical storms northward into the Southwest US. If not us, then those dry areas of New Mexico and west Texas virtually guaranteed for some tropical air.
Yesterday’s clouds
10:53 AM. Mostly Cirrus uncinus, bisected by a contrail.2:38 PM. Cumulus humilis and fractus boiled up out of 100 F plus air at the surface. Tops warmer than -10 C, so no ice, just those thin patches of Cirrus on top.3:08 PM. Cirrocumulus atop Cumulus fractus clouds.
Nice Altocumulus around this morning, but moisture is really confined to that level, not deep enough for rain at the ground. The Cumulus that form this afternoon will have bases around 14,000 to 15,000 feet above the ground. They should be deeper than yesterday, and so ice is likely to form in the larger ones (and we hope that you will log that in your daily cloud diary), but only tantalizing virga is likely, maybe with some brief windy periods near them.
Meteorologists have called stagnant pressure conditions with inflated temperatures “stagflation” for as long as I can remember, which is not that long. Anyway, that’s what we have before us, pretty much the same old thing, day after day, except for some really nice Cirrus patterns in the sky to go with those 100-110 F temperatures we get this time of year. You can see the upper level moisture stream coming over us here, from the Huskies, if you’re interested.
Mind-starting to drift off center now….
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Weather extreme note
If you noted the record-tying “trace” of rain at Vegas back on the 25th and were pretty happy about it, well, you’re going to be put out by this NWS message, passed along by climate guru and mischief maker, Mark Albright, just yesterday. Apparently, the NWS has been concerned over this record tying event for some time:
“RECORD EVENT REPORT…CORRECTED
NATIONAL WEATHER SERVICE LAS VEGAS, NV
1059 PM PDT THU MAY 29 2014
…NO RECORD DAILY MAXIMUM PRECIPITATION WAS TIED AT LAS VEGAS SUNDAY...
DUE TO AN EQUIPMENT ISSUE WITH THE PRESENT WEATHER SENSOR AT THE
MCCARRAN INTERNATIONAL AIRPORT ASOS, A FALSE REPORT OF A TRACE OF
PRECIPITATION WAS REPORTED ON SUNDAY, MAY 25TH. AFTER FURTHER
INVESTIGATION, THIS WAS DETERMINED TO BE INCORRECT. THEREFORE THE FINAL PRECIPITATION TOTAL FOR SUNDAY, MAY 25TH, IS 0.00 INCH AND THE DAILY PRECIPITATION RECORD WAS NOT TIED.
THE ABOVE INFORMATION IS PRELIMINARY AND IS SUBJECT TO A FINAL
REVIEW BEFORE BEING CERTIFIED BY THE NATIONAL CLIMATIC DATA CENTER.
$$”
Hope I didn’t spoil your morning.
On the other hand, you wonder what the NWS meant, “after further investigation…”? What might they have done to remove an extreme weather event, one that tied a record?
Let’s “jump in” and see what we can find out about this record-tying mystery. First, let’s pull up radar-derived precip maps for May 25th and May 26th and see if there is any chance it rained on the 25th. We have to do two maps since the end time of each radar precip map is for the 24 h period ending at 5 AM, whilst the record is for midnight to midnight of the 25th. Below, from WSI Intellicast are those two 5 AM AST maps in chronological order:
:
We can see that it DID rain in the 24 h ending at 5 AM AST on the 25th at McCarran Field, LAS, but not AFTER 5 AM ending on the 26th (map on the right.
But when did the weather observing machine think it rained?
By pulling up the hourly observations in text form below, we can see that the machine thought that rain began at 1519 Central Universal Time (8:19 AM AST) and rained for 11 minutes, ending at 1530 CUT. “RAB” means “rain began, truncated to minutes after the hour).
Looking further, we can also see the text words “SCT” and “CLR” for the time periods in which rain was reported. Furthermore, the the “numbol”, “>120” , means no clouds below 12, 000 feet above ground level.
Can it rain to the ground from clouds higher than 12,000 feet above the ground? Its fairly rare, but it happens, as we Arizona sunbirds know from just the past couple of days when sprinkles fell from such clouds.
However, investigating even farther, we find that the machine is also indicating “CLR” or “SCT” conditions, meaning CLEAR or SCATTERED clouds above 12,000 feet.
Can it rain from CLEAR skies, too few clouds for the sensor to detect overhead? Or SCT skies? It has happened that the machine reports SCT conditions on a RARE occasion when a little Cumulonimbus is passing overhead. I think it was reported from Douglas last summer; thunder, too. Very odd, but not impossible.
But what we don’t see is any “VCRA” report, that is, the coding for “rain in the vicinity” that would be inserted next to the column of “10s” above if there had been any as detected by radar.
So, after a few hours of investigation, we have absolved the NWS of having improperly removed an extreme weather event: the trace of rain was, in FACT, erroneously reported from the McCarran Field weather observing machine.
(Actually the point of this rather tortured writeup is to expose you to a little of our weather reporting language called, METAR. You can read about it here pretty good. You can get those METAR reports from many places, here’s one.
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A hodge-podge of cloud scenes from the recent trace of rain rainy day
(Counted over 100 drops on a wide area of pavement during the many, many sprinkle episodes two days ago; each one, I noticed, dried up in about two seconds, too.)
The tropical fetch coming to Catalina (shown here yesterday) is from the remains of now strong hurricane Amanda, unusually strong for May for that matter, a month in which tropical storms in the Mexican Pacific are pretty rare, let alone have a Category 4 hurricane down there. Has sustained winds of 140 mph now, BTW.
When pointing out the tropical finches yesterday, was not aware that the low down there was, in fact, a hurricane. (Maybe I shouldn’t point things like that out, causing the one reader to lose confidence…. Too late now.) Check out this loop from the U of WA for the “pinhole” signature of strong hurricanes. Really happy to report that rain is on the way as May closes out (29th-31st are best chances for rain here).
Reprising yesterday’s cloud day…
1) Your day began with sprinkles from a cloud deck based at around 12, 000 feet above ground level (remember, too, that you can skip the “added value”, incremental approach below by just going to your great U of AZ time lapse movie. I thought it was really very pretty for yesterday):
5:32 AM. RW– (very light rainshowers) were falling from what could be called a Altocumulus opacus deck with scattered taller turrets embedded in it, ones that produced the sprinkles.
2) clearing from the north:
6:24 AM. The shallow nature of most of the Ac deck is apparent as the backedge moves toward Catalina.
3) once the clearing arrived, small Cumulus began developing on the Cat Mountains and “?”:
9:36 AM. I have no idea. Move along now to the next photo.
4) nice small Cumulus all around, sometimes filling in to make it seem like a Seattle day in spring, with patches of Cirrus on top:
10:16 AM. Cumulus humilis and fractus (those shreds) and that beautiful Cirrus seemingly spreading its icy arms out (spreading likely due to perspective).
5) Was there artwork in the sky? You bet. A niche developed here I immodestly remind you, is that of cloud bottom photography, something I enjoy, and I think you do, too. Below is one of the best ones of the day from the Cloud Bottoms Collection:
10:16 AM. Bottom of Cumulus humilis, maybe mediocris even, that was over ME. You look up, wondering, how deep is it? Will it form ice and rain on ME? Maybe graupel will fall out….since those are the first particles out the bottom of a growing Cumulus that is transitioning to a Cumulonimbus… So much to think about when a bottom is over you. Yours for $1,800, if you call now.
6) Late morning fill in:
11:23 AM. Cumulus and Stratocumulus dominated the sky for a time; looked threatening, but no frizzy ice seen around the edges. No ice; no precip or virga. Pretty, though, with those shadows and sun breaks on the Cat Mountains
7) Smoky sunset (not a western singer, though it would be a good name for one):
7:06 PM. Drifted down from the north. Likely hours old, judging by the striations in it (not well mixed out and homogeneous as would be smoke that’s days old). Could not find source in satellite imagery right off. I see that some of that layer is still visible to the SW this morning.
The End.
5)
6) Wildfire smoke drifts down in a thin layer from the N to spoil our sunset. Note the reddish orange sun, a good sign of smoke and smog particles, tiny ones (typically, if you really want to know, that are 0.01 to 0.1 microns in size) that eviscerate the shorter wavelengths of sunlight so that only the reddish ones get through.
Like you, my heart started pounding when that bank of thick clouds on the horizon got close enough to see that there was a rainshaft to the ground with a minor Cumulonimbus on top of it (ignoring the fact that you could’ve been hanging out by the radar all day).
6:47 PM. Cumulonimbus with rainshaft to the ground slowly approached near sunset yesterday. Big dust plume also visible to the right of the shaft a little later.
Today, the heart of the cold air and best moisture are over us and TODAY we will get those local icing-out Cu and small Cbs with sprinkles here and there. Measurable? Not so sure. Will be lucky. LTG in the area likely today, too.
If you’re a low temperature anomaly centric person at this time of the year (in texting, “LTACP”, or just “LTAC” for short), you will likely enjoy today’s 10 degrees or so below normal afternoon maximum, chillier even with outflows from virga and the scattered light showers around.
More later, photos, too… Behind on animal chores now.
Yesterday’s clouds
I thought it was a pretty nice day for you, though a little disappointing due to the late arrival of the minor rain threat mentioned above. You had quite an array of clouds to discuss in your cloud diary, which was good.
Below, I reprise them for you:
6:30 AM. Altostratus, the State Cloud of Arizona I think; Altostratus. We see a lot Cumulus, of course, but sporadically in the winter following a storm or trough like today, and in our summer rain season, but Altostratus we see year round.
8:49 AM. Mostly Cirrus uncinus (hooked, or tufted at the top).10:03 AM. Accas: Altocumulus castellanus. According to my cloud chart, it could rain with 6 to 196 hours after you see these clouds.
Sure, there was a little mischievous wind in the early afternoon, BUT, as a day in late May in Catalina/Sutherland Heights zone of Arizona, wherein the temperature is less than 100 F, well, it was pretty darn great. Another one is on tap today just like yesterday today, too. Feeling sad about the early, northerly ejections of “snowbirds” who thought because of the warm winter, May would be an inferno here and are missing some splendid weather. Doesn’t work that way. You just don’t know.
Lot of interesting clouds yesterday, too, real cold ones. Those Cumulus that formed in the late morning and afternoon started producing ice almost immediately. Wonder if you caught the first ones over there beyond the Charouleau Gap around 11 AM? They did not look as high-based as they were, thus, as cold overall, dad-gum, those cloud bottoms were running around -10 C (14 F)!
How high off the Catalina ground were they? Oh, about 13,000 feet, or about 16,000 feet above sea level (about 550 millibars). I woulda guessed, as you would have, about 8,000 feet off the ground when I first saw them forming (and not looking at the temperature and dewpoints, from which you can make a pretty good calculation of the cloud base height). From the Cowboys at the U of Wyoming, this sounding for TUS yesterday afternoon:
The Tucson balloon sounding for yesterday afternoon, launched around 3:30 PM, ascends at about 1,000 feet a minute.
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Weather Hints for Every Day Use by “Art”: You can calculate the height of a Cumulus cloud base by taking the difference between the temperature and the dewpoint, dividing it by 5, square that number, add the number you started with, and subtract the square root of 2.
DId I get the number you started with?
(Actually, stop at “dividing by 5”, multiply that number by 1000, and you’ll come out just about right. Yesterday, 85 F temp, 20 F dewpoint, leads to 65 F difference, divide by 5, you get 13, and times a thousand is an estimated CUMULUS cloud base of about 13,000 feet above you, not too bad).
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Continuing….. Since bases were so cold, tops were exceptionally cold, too, for shallow Cumulus and started producing ice when they were only about 1,000 to 3,000 feet thick, with cloud top temperatures of -15 C to -20 C (about 4 F to -4 F). Some of the highest tops, all east of us, and mostly on the east side of the Catalina Mountains, were likely as cold as -30 C (-22 F).
You can see yesterday’s small Cu spewing ice in the great U of AZ time lapse movie here. Only plays for one day, though.
You may also have noted in your cloud diary the bifurcation in the Cumulus array of yesterday. Almost no Cumulus west of Catalina, and plenty in the east half of the sky, appearing to be largest in the distance in the east. We were literally on the edge of the moist plume from the south that was hoped to end up been west, with us deeply embedded in it, and where measurable rain might have fallen here as it did east of us yesterday. Oh, well.
Today, with a low center passing over us tonight and a blob of Pacific Ocean air in it, and while that air is cold and pretty dry aloft, it will be a little more moist and so cloud bases today should be a little lower, and warmer, than yesterday’s. That means a little more water condensing in them than in yesterday’s clouds, and a greater chance of sprinkle here. Hoping for measurable, but its probably less than a 50-50 shot at that. Likely will be some thunder in the area of SE AZ, too. And, as always with high cloud bases, gusty winds that arise due to virga and rain falling through the dry air below cloud base. (Yesterday afternoon’s gales in the Sutherland Heights, momentary blasts of 40-50 mph, were NOT due to virga, but a rather to something I didn’t see coming, maybe a smallish low center–nothing really showed up on the maps.)
You will also see in the above loop that our low takes its time moving along, and will keep the skies interesting with Cumulus and weak Cumulonimbus clouds today and tomorrow, along with temperatures below seasonal norms for late May (aka, less than 100 F) ((Snowbirds left too soon; ice still melting off some areas of the Great Lakes!))
From the cloud vault; yesterday’s clouds
10:28 AM. Small Cu with lenticular type tops began forming in the lee of the Catalinas during a horseback ride with a friend, in case you didn’t think someone as cloud-centric as me could have a friend. Calm winds, then, too.11:08 AM. First ice! Can you spot it in the distance? Horse can’t believe that ice is forming already, and is rolling around in ecstasy, thinking about what it might mean for the afternoon.1:43 PM. Approaching low with air moving upward ahead of it, triggers a batch of Cirrus and Cirrocmulus lenticularis (really high lenticularis) upwind of Catalina and above some Cumulus fractus.3:18 PM. One of the more remarkable sights yesterday, were the small Cumulus clouds (humiilis or mediocris) that iced out. Look at ll the ice that formed in this small cloud, exiting on the left side, but dominates the whole cloud from this viewpoint. When you see this, it tells you how COLD those clouds are. First guess should be around -20 C at top when you see this much ice in a cloud this SMALL. Clouds having warmer bottoms, can have warmer tops that look this icy because ice forms in clouds at higher temperatures when the drops in them are larger (see Rangno and Hobbs 1994, Quart. J. Roy, Met, Soc.) Oh, yeah, baby, have some pubs!
6:58 PM. Iced out Cu/weak Cumulonimbus beyond the Gap, the Charouleau one, end the day. Shoot, a slight change in trajectory from the south, and they woulda been here.7:00 PM. Meanwhile, all quiet to the NW, no Cu whatsoever demonstrating the moisture edge we were on.
The weather ahead and WAY ahead
Now what I think is really interesting, which is almost everything to do with weather, is that the models are suggesting a tropical injection again at the end of MAY into early June, with a chance of a decent rain again. As you can see in the plot below from the NOAA spaghetti factory, a trough to the west of us and over California is a virtual certainty now at the end of May. That means the air above us will be, while quite warm, originating from the deep Tropics with the likelihood of clouds and precip coming up from there. Nice. Will keep me posted on these developments, in case no one else is reading this far.
