Once again we had a brief period of optical fireworks, as a rare “circumzenithal arc” developed overhead of Catalina in some Cirrus strands. Hope you saw it and bragged about it to your less observant friends. After saying that, follow it up in a moment of feigned reflection, speaking to no one in particular, with a comment about “how sad it is when people don’t notice the beauty in the world around them.” Your friend will appreciate what a sensitive person you are. That would be great!
Here are the scenes so many missed because you only have SECONDS to see them light up, peak out and disappear (but I saw it!):
9:28:31 AM. First highlight begins, center, leading edge.9:28:44 AM. Here we go!9:29:43 AM. Starting to really light up!9:29:45 AM. Zooming in…. Of course, like a rainbow, you would have to be exactly where I was to see this exact same sight, but I was alone and therefore, the only person in the world to see this.9:30:29 AM. Last little wisp of color goes over.
Whew, that was pretty much the climax of this event. Began to relax. calm down, as the possibility of seeing more “arcs”, began to fade. No more Cirrus was upwind.
Most of these I have seen have been due to aircraft-produced ice particles (“APIPs”, as named by Rangno and Hobbs way back in 1983, J. Appl. Meteor.), i. e., contrail like events produced by aircraft that occur at much higher than expected temperatures in “supercooled” clouds.
No Altocumulus clouds were around this line of Cirrus uncinus clouds at the time this passed over, though there were plenty around, however. Likely this was produced upwind by an aircraft in Ac clouds, and the Altocumulus droplet clouds just evaporated.
These aircraft produced ice clouds start out having prodigious, unnaturally high concentrations of ice, thousands per liter, and that in itself would lead, due to the competition of vapor among them, to tiny, pristine ice crystals like solid columns that would refract the sun’s light. So, that’s my thought on the origin of this line of Cirrus uncinus, the line itself raising suspicions about its origin. It extended much farther than shown in these photos, and was intermittent, likely reflecting where the Altocu was, and where there were holes in the coverage.
11:03 AM. Iridescence, about as good as it gets.11:07 AM. More iridescence. Hope you saw this, too.
Next, holey stuff.
Never seen anything quite like what happened in those quasi-laminar clouds that developed later in the morning over and near the Catalinas, so must show :
11:08 AM. Intrusions of dry air started punching holes in clouds all over.11:09 AM. Holes started to appear in adjacent clouds.11:09 AM. Zooming in at this strange phenomenon.11:11 AM. Geeminy Christmas, the sky is falling!11:12 AM. Closer to life size here. Pretty remarkable. Outside border of hole seemed to have collapsing cloud filaments supporting a localized downdraft punch.11:12: More holes began to appear next to the main one.11:14 AM. More hole craziness!11:15 AM. Wow. Look at the complexity in that hole.11:17 AM. This lenticular had an exceptionally smooth top, but a hole started to develop underneath and a little downwind.11:17 AM. Another dry air hole punch appeared. What an interesting day this has been so far, and its not even noon!
Well, as you could imagine, I could go on and on about this, with many more photos, but need to quit here. And besides, it pretty much cleared off in the afternoon, and the hole phenomenon ended.
12:49 PM. Wow, look how much thicker a seemingly uniformly thing layer of Altocumulus perlucidus is in those dark areas!! Not! Those are shadows from a higher splotches of CIrrus, some of the “uncinus” species. This is what I do here, try to pull a fast one on you.12:02 PM. The prior shot was looking S under the Ac per layer later in the day. Here’s what the sky looked like to the N a little earlier, providing the explanation for dark spots in that Ac layer. Haha, really fooled you at first!
Now, we take this break for art, and not fun:
“Saddle with Undulatus”. Yours for $1200, and, of course, free shipping!“saddle with Undulatus”, zoomed view, full-sized jpeg! Yours for $1800!
Some water was still flowing in one of the little creek tributaries to the Sutherland Wash yesterday. Nice.
1:53 PM.2:01 PM. Short-lived patch of Cirrocumulus undulatus (right) with larger Altocumulus elements (left) all at the same level. Also, if you can find it, and aircraft-produced patch of ice. Testing 1-2-3…..
Big rains in Cal mountains and Bay Area, some hill totals over 6 inches past 24 h, lower sites, 1-3 inches. Floody rains will take a big bite of out of drought during the nest 12-14 days.
Nothin’ reliably seen here, though, except passing high and middle clouds.
Then this, looking straight up when CMP first noticed it because he wasn’t paying attention:
11:24 AM.
A few minutes later, as it moved away:
11:27 AM.
What happened? How cold were these Altocumulus clouds?
(Answers printed upside down below).
There were more, off in the distance, too.
Here are a few more shots of this phenomenon:
11:29 AM. As it went over the horizon to the east. You can really see how strange it made the sky look. Note, too, the contrail from a much higher flying aircraft (at Cirrus levels).4:02 PM. Those fine trails of virga (center of photo, trailing in strands to the right), were “probably” created by an aircraft. They don’t look natural to me, though when this happens without producing a ice canal or a clearing, its much more difficult to be certain. Those trails look too flat, a result of likely very high concentrations of ice crystals, all of which remain small due to the competition for the vapor in that cloud, and would be too small to collide with cloud droplets. There would be no hole or canal because the rise rate of the layer is producing droplet cloud faster than the ice crystals could take it away. In the prior photos with the ice canal, which did not fill in, you can guess the rise rate of the layer that produced the Ac per was nil. Those clouds did not fill in as the ice settled downward and out of the layer. Whew, lotta typing just then.5:23 PM. Numerous holes were being punched in that cold Altocumulus layer out to the southwest of us. If you are pretty observant, you know that there is an airway out there, often filled with contrails. These, though are likely produced by those aircraft below the normal Cirrus levels, but rather would be ones departing or landing, in descent or climb modes, maybe from TUS?5:41 PM. Zooming; pretty virga, but not natural.
Now, we’re really quitting because I have other things to do, ones that have to be done, like discovering why our attic has so many rodents in it? Well, one, every so often, dammitall. Why is life one problem after another?
The pre-dawn TUS sounding, PRESUMMED representative of that Ac per layer. It would have been where the two lines pinch together, and if somehow you can read the temperature, its between -25° and -30° C.For the evening aircraft effects, there are two choices of layers. Probably was the lower, warmer one IMO.
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Answers not printed upside down instead:
It was an ice canal created in a highly supercooled layer of Altocumulus perlucidus. How cold? Whenever you see one of these in a middle cloud like Altocumulus, you can guess that its colder than -20° C. They’re rarely seen in warmer clouds. The TUS soundings suggested this layer was between -25° and -30° C. It mostly was ice free, bur regions of some slight (natural virga) were seen,
It was probably created by a jet, though the rarer prop aircraft can’t be ruled out. Seems to be associated with cooling around prop tips or some say over the wing cooling momentarily below around -40° C, though visually I would offer that its from the water-loaded exhaust, at least in jets, rather than air cooled as it goes over the wing.
0.24 inches was recorded after 7 AM yesterday, bringing our voluptuous rain total to 0.95 inches1. How nice.
Dry spell ahead now, maybe a LONG one. “Fiddle-dee-dee.”
Yesterday: another day shallow precipitating clouds and “ice multiplication”
Seemed to be another day of “ice multiplication” here in southeast Arizona, a term that was coined in 1969 by Peter Hobbs of the University of Washington when he and his group reported that clouds were snowing on the peaks of the Olympic Mountains when the cloud top temperatures were warmer than -10° C (14° F). They had a hut on the top of Mt. Olympus at 7,000 feet! Lots of stories about that experiment, many swirling around Abdul Alkezweeny, a Peter Hobbs grad student in those days. An aircraft with skis landed up there to bring supplies! Imagine. (Yours truly was not embedded in the Hobbs group at that time.) It was an exciting time in that group, prior to the acquisition of their first research aircraft, WWII B-23 “tail dragger.” Peter himself, did not fly in this with RARE exception. Many flights were quite sickening, bumping around in Cumulus and small Cumulonimbus clouds, spinning around power plants stacks, wings vertical to ground….
In a nostalgic mood, posting this photo of our venerable B-23 research aircraft in which I spent SO MANY hours!
His group’s observations, however, were not the first, but were among many airborne and ground reports in the mid and 1960s that left jaws dropping about how much ice was in clouds at these moderately supercooled temperatures, even in clouds with tops as warm as -4° C. It was believed, in various ways that ice nuclei measurements were made on the ground, or in aircraft measurements, that not much ice would be found in clouds until the top temperatures was lower than -20° C. In fact, it was generally believed that only about one ice particle per liter would be found in clouds with tops as cold at -20° C, while actual observations were telling a much different story.
This discrepancy between measured ice nuclei concentrations is a scientific enigma that is still being investigated today! And it appears that me and you cloud maven juniors out there got to see it again yesterday, the second day in a row to see an cloud-ice enigma (“nigma” for short)!
Let us continue this module by examining the assertion of “ice multiplication” with the TUS balloon soundings for yesterday morning and evening as rendered by IPS MeteoStar:
The TUS rawinsonde balloon data from yesterday morning. Launched around 3:30 AM AST.The TUS rawinsonde profile yesterday afternoon, balloon launched at about 3:30 PM AST.
These soundings strongly suggest at the start and end of the day, that coldest cloud tops were warmer or no colder than -10° C.
However, the fly in the oatmeal here is that a cold front and associated wind shift came through in the mid-morning hours, heralded by an little arcus cloud, and cloud tops would have been somewhat colder during that period of rain; we don’t know for sure how much, and satellite imagery suggested lower temperatures, though possibly due to over-riding CIrrus cloud above the “Nimbostratus” layer that produced the steady light rain.
However, the rain before the front went by, and the very light rain showers that fell in the late afternoon were likely well represented by the TUS soundings. That’s my case! Wish I’d had a cloud-instrumented yesterday and the day before. Woulda got a paper out of it: “Ice multiplication rampant in Arizona!”
Yesterday’s actual clouds
No more hand-waving…. Let’s see if it really was raining near the time of the TUS soundings above. Picture of the day:
5:18 PM. Rainbow goes INTO a RAIN GAUGE! Amazing. Proves that it was raining, though very lightly (RW–) at 5:18 PM, when the sounding profile was likely valid for these light showers. Q. E. D.! Yours for $2,000, today only. Should get a lot of money out of this photo. I had to practically have the camera on the ground to get the right alignment and illusion. 8:08 AM. Misty, light rain showers shower on the Catalinas and in Catalina itself.
8:50 AM. Misty light rain continues from relatively shallow clouds. No shafting observed, something that would suggest much taller cloud tops. These were likely “mounding” up there, like rolling hills, mounding the most prior to releasing slightly heavier rain. Here’s where you would be thinking, “Could this be ANOTHER ice multiplication day? Wow, if so.” And, of course, the thought of it being a warm rain process day (no ice, thank you) can’t be ruled out either, since rain can form at below freezing temperatures in clouds, though supercooled raindrops are the most vulnerable to freezing at high temperatures, to go a little deep here, and complex the interpretation some.
That was phase one of yesterday’s weather, rain from shallow clouds.
Phase 2 is, “The front marches in across the OV! Cloud depth not so certain, but is probably not real deep, as inferred from the disappointing amount of rain that fell so lightly from the frontal band in spite of its dramatic entrance, fronted by an arcus, wind shift cloud.”
9:55 AM. Here comes the front and arcus wind shift cloud!10:06 AM. Here the approaching front and wind shift appeared to have jacked up a cloud top near Pusch Ridge. Was thinking, as you were, maybe we’ll get some thunder today.10:14 AM. Arcus cloud rolls fast across the OV; rain follows.10:19 AM. Arcus cloud passes over Sutherland Heights, and light curtains of rain begin to fall from it.11:26 AM. The end is near. The sun became visible after only an hour of steady, very light rain, and a tenth of an inch of rain. Thought there might be a gush in this, but, no. This also points to shallow, mounding or even flat cloud tops, not tall ones. This was not a good sight.
But, as those who live here know, some of our best scenes are AFTER after the rain has stopped and the skies partially clear. Yesterday was no exception. But first, the Stratus, which you don’t see too often:
1:09 PM. Looking north at a Saddebrooke highlight. Stratus is beginning to break up out there.1:11 PM. Stratus in the cold air following the frontal passage (“FROPA”, in weather speak or texting). Not budging yet.1:35 PM. Yep, only 25 or so min later, this! So pretty. Stratus fractus lining the area around Charouleau Gap.2:30 PM.2:57 PM. Cumulus puffing up by the minute. Will they form ice?3:04 PM. Just a pretty scene of Cumulus over there toward Saddlebrooke.4:02 PM. A bit of a surprise as a group of precipitating Stratocumulus like clouds came rushing in. No shafts, suggesting tall tops were seen, so likely again just mounding tops up there.5:24 PM. As the last sprinkles ended and the sun peaked through an opening to the SW, our mountains and clouds lit up with an orange tint. As the air cooled the Stratus fractus clouds (highlighted) again were once again straddling the side of mountains near Charouleau Gap.
Looks like only streamers of high and middle cloud from the tropics as California gets blasted with extremely heavy rains over the next two weeks. Totals in favored central and northern California coastal ranges, and in the central and northern Sierras will fall between 20 and 30 inches of rain during this period. A great place for you and me to be would be near the King Range, Shelter Cove (see below), or Honeydew to see those pounders.
Part of Shelter Cove, CA, with King Range in the background. A coastal jet rams the King Range and causes prodigious rains from ordinary looking storms. Average precip more than 100 inches, farthest south point for such a high average rainfall on the West Coast.
The End
—————————– 1The online gauge is a Davis tipping bucket. It has been consistently under-measuring totals recorded in the NWS 8-inch diameter gauge, and the 4-inch diameter, ground-mounted (it sits on the ground among grasses and weeds) CoCoRahs gauge. CoCoRahs is a national organization of rain and snow measuring nuts (haha, just kidding-they’re really precipophiles like me) all over the country and overseas as well. You can find them here. Part of the reason for the under-measurement of the Davis instrument is loss due to wind. That tipping bucket sits up at about 6 feet off the ground, thus sees a lot more wind than gauges on the ground. A gauge on the ground, away from tall objects, is always the best way to go! The reason for this explanation is because if you go to Wundermaps or Weather Underground and see the total for this site, it is ALWAYS going to be low compared to the actual amount that fell. This is a degradation that has come up over the past year or two.
3:55 PM. Rainbow fragment and solar home, an extraordinary combination.. It was yesterday’s visual highlight. Yours for $1995.95. And, if you order now, we’ll throw in a second, exact copy of this extraordinary, magical scene FREE!
Here’s a nice one from the day before as the clouds rolled in, starting with Cirrus and Altocumulus, lowering to Stratocumulus later in the afternoon.
Yesterday’s clouds; an extraordinary day with a little drizzle amid light showers
Hope you noticed the true drizzle that occurred yesterday, namely, fine (larger than 200 microns, smaller than 500 microns in diameter), close TOGETHER (critical to the definition of “drizzle”) drops that nearly float in the air. They may make the least impression, or none, when landing in a puddle.
When you see drizzle, you have the opportunity of chatting up your neighbor by educating them informally to what drizzle really is (many, maybe most, TEEVEE weatherfolk do NOT know what “drizzle” is, btw), and 2) by telling your neighbor, if he/she is still listening to you, that the droplets in the clouds overhead must be larger than 30 microns in diameter, or better yet, “larger than the Hocking-Jonas diameter of 38 microns, at which point collisions with coalescence begins to occur” and “drizzle is not produced by ice crystals in the clouds overhead; they’re not enough of them to produce ‘fine, close together drops.'” Your neighbor has likely left the building at this point, but, oh, well, you tried.
Here, in Arizona, shallow clouds, such as we had yesterday, hardly ever can produce the broad droplet spectrum in which clouds have droplets larger than 30 microns in diameter. Its because this far inland from the ocean, where the air is very clean, the air has picked up natural and anthro aerosol particles that can function as “cloud condensation nuclei” (CCN). As a result of ingesting dirt and stuff, clouds have too many droplets here as a rule for the droplets in them to grow to larger sizes. They’re all mostly less than 20-25 microns, sizes in which even if they collide, they can’t coalesce.
In “pristine” areas, if you go to one, such as on a cruise out in the oceans, droplet concentrations in clouds are much lower, and even a little water that might be condensed in a shallow cloud can produce a broad spectrum, one that extends to droplet larger than 30 microns.
So even little or shallow layer clouds can precip over the oceans, produce drizzle or light rain showers (in which the larger drops are bigger than 500 microns in diameter). Of course, here we recall that the (whom some consider “villainous”) geoengineers want to stop drizzle out over the oceans so that clouds have longer lifetimes, are darker on the bottom, and reflect more sunlight back into space.
Those guys can be lumped into the same ilk as those who want to change the color of the sky from blue to whitish or yellowish by adding gigantic amounts of tiny particles in the stratosphere, again for the purpose of cooling the planet! Unbelievable. Please ask before doing this!!!
A Pinatubo sampler for what “geoengineering” would do to our skies, say, sunsets in particular. I took this photo from the University of Washington’s research aircraft in 1992 off the Washington coast in onshore flow. But we saw these same sunsets, sunrises, yellowed by the Pinatubo eruption of June 1991 everywhere we went, including in the Azores in June 1992.
OK, pretty boring, whiney, really, so inserting picture of a nice horse here to make people feel better if you’ve been depressed about what our scientists have been pondering to do about global warming other than controlling emissions:
8:57 AM. Zeus. Led cloistered life for 13 years; likes to bolt, now that he’s getting out on the trails.7:40 AM, yesterday, Dec. 31st. The low hanging Stratocumulus clouds, about 1500 feet above Catalina, and the mountains had a bit of an orange tinge. It was probably due to sunrise color on a separate much higher layer.
Later….drizzling Stratocumulus, same view:
10:30 AM. Stratocumulus praecipitatio, if you want to go “deep” into cloud naming. “Stratiformis”, too, covers a lot of the sky. Note misty-like view, lack of shafting.12:48 PM. More Stratocu P., an example of those clouds in the distance that kept dropping little and light rain showers on Catalina.1:01 PM. Highlighting amid the RW– , (weather text for “very light rain showers”). Stratcu P., with maybe Stratus fractus or Cumulus fractus below. The shadowed, dark shred clouds in the mddle would be Stratus fractus IMO.3:55 PM. Zooming in on that pretty rainbow. You know, this is a cloud heaven here. I hope you all appreciate it! Maybe that’s why I get upset over “geoengineering” and changing the sky anywhere.3:57 PM. Between showers, but new ones erupted upwind. This one have a shaft, implying a higher cloud top than the prior, non-shafting clouds that brought us semi-steady RW–.
The second extraordinary thing about yesterday was that the top temperatures of these clouds was around -10° C (14° F), temperatures that ice does not form act as a rule in Arizona. To get ice at temperatures that high, you also need larger cloud droplets, and they have to occur in the -2.5° C to -8° C range. In this range, it was discovered that falling ice crystals, mostly faster falling ones like “graupel” (aka, soft hail) when colliding with larger drops, ice splinters are produced. The cloud droplets must be larger than 23 microns in diameter in THAT particular temperature zone, something that would occur more often in our warm, summer clouds, but would rarely be expected in our winter ones.
Why?
Again, it goes back to clouds in inland regions ingesting lots of natural and anthro aerosols that cut down on droplet sizes in clouds (by raising droplet concentrations in them). Our recent rains have helped cut down on that process on ingesting dirt, for sure, and was a likely player yesterday. Furthermore, our winter clouds are moisture challenged relative to the summer ones with their tropical origins and high cloud base temperatures, a second reason not to expect larger droplets in our winter clouds.
Here is the TUS sounding with some writing on it for yesterday afternoon from IPS MeteoStar. (Satellite imagery was also indicating warmer than usual tops for precipitating clouds yesterday.):
The TUS balloon sounding (“rawinsonde” in techno speak) launched at about 3:30 PM yesterday afternoon. Balloon rises at about 1,000 feet a minute, FYI. Typically they pop up around 100,000-120,000 feet! Instrument package is parachuted down so it doesn’t conk somebody on the head. Sometimes they are found and returned to the NWS and re-used! How great is that?
Here’s the punchline: If clouds are drizzling, then they are ripe, if the tops get to lower temperatures than about -4° C for what we’ve termed “ice multiplication” or “ice enhancement”. A very few natural ice nuclei at temperatures between -4° and -10° C, say, starts the process, those forming “soft hail” which then leads to ice splinters. This is the leading theory of this anomaly of ice in clouds at temperatures only a little below freezing, if you think 23° to 14° F fits that definition.
There are exceptions where this process did not explain the ice that formed at such high temperatures, so standby for further elucidation about how in the HECK ice forms in clouds at some point in the future.
As usual, no time to proof, so good luck in comprehending what’s been written.
The weather just ahead:
The second main rainband is just about here at 9:25 AM. Cloud tops will be deeper and colder than in the prior rains, raising the possibility of some thunder today, and maybe another third of an inch of rain. Watch for an windshift line cloud (“arcus” cloud) might well be seen today. That’s always dramatic and exciting here in Catalina cloud heaven.
What a day for cloud maven juniors and me, too, watching the Altostratus opacus (but sometimes “translucidus” cuz you could see where the sun was) become Altocumulus! It happens pretty often and is the result of lowering, and warming of the cloud tops, but I need to generate some excitement on an otherwise somewhat dull day.
What else is happened as tops warmed? Good-bye virgae (“virga”, in plain speak), except in a couple of locations that raised the question, “Was it hers (Mother Nature’s) or ours (aircraft effects)?”
The TUS balloon sounding through all that Altostratus opacus virgae. Launched at about 3:30 AM. The top temperature is so cold (-60° C, -76° F) we don’t even want to know here in Arizona that such temperatures are possible. So, you can imagine all the ice that might form in a moist layer of air. The bottom is even cold at nearly -15° C, there were the temperature jumps out to the right. This is a situation we call “overrunning”, where warmer air is going over a colder air mass. This cloud was about 22,000 feet thick, 7 km at this point.
The slight spread between the two lines illustrates the classic representation of what we measure when the balloon passes through an all ice crystal/snowflake cloud like this version of Altostratus was yesterday morning. The humidity element on the balloon measures the humidity relative to liquid water, not ice, so there will be some spread between the dew point temperature (line on the left) and the temperature (line on the right) when the balloon ascends through an ice cloud. Saturation with respect to ice is indicated here in that deep “overrunning” layer, something also likely to happen tomorrow to the writer’s “company” fubball team tomorrow.
And here’s the TUS sounding launched yesterday afternoon when we only had Altocumulus opacus clouds, just as dark as Altostratus opacus, but much thinner. Tops around -10° for the most part, but there may have been some turrets to around -20° C. The balloon almost certainly passed between clouds, did not go exactly through a Altocumulus cloudlet. Don’t worry if you can’t make out the actual temperatures on the lines sloping up to the right, just take my word for everything I say. You can easily see how much it dried out in the middle and upper cloud regions between the morning sounding and this one.
Yesterday’s clouds and the transition
8:29 AM. Altostratus opacus virgae (has some downward pendants of ice and snowflakes coming out of it). The TUS radar had some sprinkles showing up here and there.8:29 AM. Altostratus opacus virgae (has some downward pendants of ice and snowflakes coming out of it). The TUS radar had some sprinkles showing up here and there. If this seems familiar, the caption is identical with the prior one. Redundancy is one of the niches we practice here, mostly in cloud photos of the same thing.
Now let’s look over here:
8:29 AM. The same.9:19 AM. “Thin spots in overcast”: we used to say that a lot in our human weather reports of ages gone by. Here the thin spot makes this Altostratus translucidus.. While there is an irregular look to this Altostratus due to virga hanging down, there is no indication of liquid water elements, ones that would show up as sharply-outlined darker elements. While this is hours later than that morning TUS sounding, it is likely that in spite of this thin spot, the Altostratus layer was still many kilometers (thousands of feet thick). Ice crystals and snowflakes are far less numerous than droplets in liquid clouds, and, therefore clouds composed of ice are more transparent given equal depths. Compare the visibility in a dense fog with being in a light snowfall.9:38 AM. Example of a some sharply-outlined liquid clouds embedded in the Altostratus layer have formed. The growth of ice crystals and snowflakes is enhanced in liquid clouds because they represent regions where it is saturated with respect to WATER, and highly supersaturated with respect to ice (the relative humidity with respect to ice is well over 100%). Also, if the droplets in these clouds are large enough (larger than about 15 microns in diameter) they can be collected by the falling ice and snow, adding to their mass of those, causing them to fall faster.10:29 AM. Had numerous, dramatic outbreaks of mammatus around this time, probably representing the fall back of turrets on top of the Altostratus as this time. We will say no more about mammatus since the author has tended toward the prurient to break up the tedium in past notations about” mammatus.” This might be viewed as an upside down look at the cloud tops at this point, BEFORE they collapsed and dropped below the main bottom of this layer. At the top (rumpled area), regions of a liquid cloud layer are beginning to appear, a sure sign that tops are receding.11:55 AM. Moving along,looking upwind across the Oro Valley. Still looks composed mostly of ice (Altostratus opacus virgae here), but liquid clouds are on the far horizon.1:21 PM. Altocumulus opacus rules. The deep icy cloud is all gone by now. No virga. Notice, too, in spite of being less than a kilometer thick, this cloud looks as gray as the Altostratus that was many kilometers thick. The droplet concentrations in a liquid cloud such as this might be 200, 000 per liter, while the ice concentrations in that Altostratus cloud were likely in the 10s per liter. The smaller particles in Altocumulus clouds, average perhaps only 15-20 microns in diameter also are able to reflect far more sunlight back into space, and less sunlight reaches the bottom making it darker. In contrast, the (ice) particles in the Altostratus would be hundreds of microns to millimeters in diameter (i.e., precip-sized).2:22 PM. Looking around at these cold Altocumulus clouds, generally not showing virga, you begin to wonder if those areas you do see have been the result of an aircraft passage, as here in that little spot of virga.2:28 PM. Some breaks in the overcast allowed some nice scenes to fall upon our mountains. Here, the Charouleau Gap is highlighted.
From the global ingest of data at 11 PM AST last evening. Indicates that green Catalina will be in the half inch to three quarters of an inch between now and New Year’s Day afternoon. Comes in two segments, the first overnight tonight, and then another starts New Year’s Eve. Seems reasonable. Probably not quite reasonable is the red on the Cat Mountains, indicating 3-4 inches accumulation during this time, probably a bit overdone. Both storms are rather small in size, so the amount of rain depicted in these model runs has varied a lot. But, they seem to be settling on something decent. Seems the least we’ll end up with has to be more than a third of an inch, worst case scenario. See Bob and the NWS for a good look at these incoming events. We’re mostly about clouds here.
Undercutting flow from the tropical Pacific is on schedule. So, a good chance for major rains along the southern portions of the West Coast in a few days, with a pretty good chance they’ll leak into Arizony.
What a gorgeous day yesterday was with deep blue skies dotted with Cumulus and one or two shallow Cumulonimbus, highlighted by our snow-capped Catalina Mountains. After the brief warm up, more storms ahead for Catalina!
Yesterday’s clouds
10:23 AM. By this time Cumulus were popping up all over, and with the temperature at just 10,000 feet above sea level (7,000 feet above Catalina) cloud mavens everywhere were pretty sure ice would eventually form in lots of Cumulus.10:24 AM. Shallow Cumulus congestus (left side) converting into an equally shallow Cumulonimbus capillatus (right half of cloud). This scene from a fairly primitive area of Arizona.10:26 AM. Pretty scene over Saddlebrooke.10:37 AM. Ice, there it is. Even shallow clouds spewed ice crystals and or small snowflakes (clusters of individual ice crystals.
Explanatory module below
The TUS balloon sounding, launched at about 3:30 AM yesterday morning from the campus of the University of Arizona Wildcats.10:27 AM. Wintry scene #1, view toward the Charouleau Gap, and why do the French make spelling so hard?11:04 AM. “Ice, there it is!”, to paraphrase a song from “In Living Color.”11:12 AM. Wintry scene #2. View is toward the Charouleau Gap.11:12 AM. Icy, but shallow Cumulonimbus cloud heads toward Catalina spewing a light rain shower and soft hail called “graupel.”11:44 AM. Wintry scene #3.12:32 PM. Not an advertisement for the University of Washington Huskies sports powerhouse, but rather a demonstration and graupel did, in fact, fall from our shallow Cumulonimbus clouds yesterday. BTW, the Washington Huskies play the NFL-ready, #1 Alabama Crimson Tide on New Year’s Eve at 1 PM AST in a fubbal playoff game. It would be great if you watched, raising viewer numbers, and possibly therein, the revenue stream flwoing into the University of Washington (from which I emanated). Oh, there appears to be a conical graupel there on the left. Graupel falling through a cloud of droplets often stays oriented with one face down, and that face collects all droplets that are freezing on it making that downward facing side, as you would imagine, bigger than the rear part, and so you get a pyramidal-shaped piece of soft ice. If it mainly tumbled on the way down through the cloud, it would be pretty spherical. That white streak on the right is one that’s falling.11:12 AM. Another ice producing candidate forms in cloud street aligned with Catalina. Couple of drops is all that came out of this.3:18 PM. Very shallow, ice-producing clouds. Few in the area had ice at this point in the afternoon, and a very tedious inspection of these clouds, comparing them with surrounding clouds, suggested that their tops were just a bit higher than the ones around it that did not spew a little ice.The TUS balloon sounding launched at 3:30 PM AST, also with writing on it.5:06 PM. Wintry scene #4 Pretty, eh?5:32 PM. Stratocumulus with red liner. Nice.
After the brief warm up ahead, still looks “troughulent” and stormy in the SW as December closes out, continuing into January.
The “entrance” of our major cold front yesterday was spectacular! Hope you were able to stand upright in the wind, gusts to 60 mph, that just preceded it and saw that arcus cloud march across the Tortolita Mountains and into Oro Valley and Saddlebrooke. If you didn’t, its reprised here, of course.
The arrival of the rain and front was PERFECTLY predicted1 by the U of AZ model night before last; the first drops were supposed to fall between 3 and 4 PM, and by 4 PM, there they were, framed by one of the most spectacular arcus cloud formations I have ever seen. Let’s look now, instead of wading through the whole cloud day leading up to it. Feature a lot of views of the same thing, zoomed differently, it was THAT spectacular:
3:46 PM.3:46 PM.3:46 PM.3:49 PM.3:52 PM.3:58 PM. The engulfing of Saddlebrooke.3:58 PM. And as it passed over Sutherland Heights. Not quite as spectacular appearing as elsewhere.
Here’s what the temperature did yesterday afternoon as this arcus cloud and wind shift line hit:
A temperature record (in Fahrenheit, of course) of our cold front passage yesterday. Got down to 37° F for a few minutes before the recovery started.
The End
——————————– 1CMP got a little overexcited and had rain in the area prematurely in his own forecast (i. e., rain in the area beginning between 11 AM and 2 PM), trying to go 1 up on the model. Bad idea. And no ice whatsoever was seen in those afternoon Cu that started to develop, as CMP was SURE was going to happen, eyeballs straining for ice. Didn’t see the expected precursor lenticulars, either!
Yep, a dramatic Christmas Eve storm, complete with rain and bluster, maybe even ending with a little snow, in case you’ve been in a cave for the past couple of days and haven’t heard about it. Media folks have been all over this, so am tuning it here just a bit, if, in fact, I can, for Catalina.
The wind today in Sutherland Heights will likely gust to over 40 mph from the southwest in 1-2 second bursts here , similar to the wind in the last big couple of FROPAs, so best to put loose stuff away.
In fact, the U of AZ mod from last evening sees winds of 115 mph above TUS at mid-day at just the 500 millibar level (15,000 feet or so above Catalina), a quite unusual strength of wind at that elevation, to give an idea of how strong the jet stream will be above us today. So, if it looks like the clouds are moving too fast, as in a time lapse movie, they are!
The core of that jet at 500 millibars passes over during the middle of the day, and that pretty much should coincide with the onset of rain as it usually does. So, look for rain to start around between 11 AM and 2 PM AST today based on that passage; the U of AZ mod output from last evening’s global data sees the start time somewhat later, between 3-4 PM. Be ready, though; it will come in a hurry! From IPS MeteoStar, this for 11 AM AST today, a real screamer of a jet is overhead:
Forecast of the flow at 500 millibars valid at 11 AM AST today. Its based on the global data, such as is available, from 11 PM AST last night, the most recent model prediction available.
We’ll have the usual “temperature slam” when the wind shifts to the NW here in Catalina during the FROPA late this afternoon or early evening. Looks like it will be a good 15° F drop, typically occurring within an hour, the first ten degrees in 15 min or so, with the temperature likely ending up in the mid-upper 30s. This is where some snow is possible. Imagine, a little SNOW in parts of Catalina on Christmas Eve is possible.
And with fronts/jets as strong as this, the rain band with the front should lead to at least moderate rain for a couple of hours. “Moderate rain”, probably “immoderate” in intensity for some desert dwellers and snowbirds, is 0.10 to 0.30 inches per hour. So rain will pile up pretty good during those periods of “moderate rain. ” Even a couple of hours of that intensity will lead to a substantial amount for our desert.
AZ mod (see link above) sees half inch to an inch here in the Catalina area to Mt Lemmon! That would give us a December total that’s above average, something we haven’t seen in a few months, an above average monthly total. A shot from hip from this keyboard yesterday to a friend was for a lesser total, 0.40 inches in Sutherland Heights1. Truly hope it is LOW!
One of the best sights today will be the transition in the clouds from dawn today (if any) until the jet core gets here in the middle of the day. Typically, on the right hand side of the jet (looking downwind), which is also the warmer side of it, the air is stable and its a great environment for lenticular clouds (smooth ones that hold in place, such as downwind of Ms. Mt. Lemmon).
As the jet core arrives at mid-day, which divides that warmer air from much colder air aloft on the left side, looking downwind, the lower clouds deepen up or move in, merge with higher cloud layers, ice forms begins to form like mad, and you start to see virga and precip all around. So, a pretty dramatic sky change should occur in the middle of the day today; have camera battery charged up, and maybe video or time lapse cameras ready to go as well.
Some cloud shots from yesterday’s “in between” day:
12:45 PM. Small Cumulus clouds (humilis) dot sky.4:26 PM. Stratocumulus clouds cluster around the Catalinas.5:35 PM. Nice sunset of precursor to storm, Altocumulus perlucidus deck. But what’s that over there, far right corner? Let’s go zooming, take a closer look.5:35 PM. Right there next to that tree on the right is virga, the only virga in this whole layer! And, though hardly visible, there’s a clearing above this patch of virga, a hole in the cloud deck. This layer was “seeded” at this point, that is, ice was caused to form in what otherwise were clouds composed of supercooled liquid water droplets, by the passage of an aircraft. This demonstrates what happens in any cloud of supercooled droplets when ice is introduced. The droplets evaporate, and the vapor deposits on the ice crystals, causing them to grow and fallout. You may recall that it was Catalina’s own Cloud Maven Person and Hobbs that brought this phenomenon to the attention of the airborne research community way back in ’83, something I wish I could point out everyday! (J. Appl. Meteor.) That’s why even the tiniest blip of virga caused by an aircraft is brought to your attention as often as possible!
The exciting possible weather WAY ahead
We have a penchant here for pointing out quasi-disastrous storms that appear in the models beyond the normal skill period of 7 days or so. Remember last year, when Cloud Maven Person was talking up those gigantic, Big Niño storms that would appear in the models, but not one actually occurred as shown? Typically, as we all do, we look at the NOAA spaghetti factory outputs to see if there is much credibility to those sometimes wild predictions. As in the current weather, the indications of frequent trough passages was well indicated in those crazy plots more than 10 days ago. (How much precip will come with them is very “iffy” but we’re doing well this time!)
Well, there’s another set of “doozies” showing up in the mods now, ones that roar out of the central Pacific and into California, just like we expected with last year’s Big Niño! How odd. Those kinds of trajectories over the warmer waters of the eastern Pacific lead to the heaviest of all rainfalls in California, and heavy amounts here in AZ. Here’s my talking point, this:
Valid in only 312 h from now! Look at that “low rider” trough off southern Cal! This is SO EXCITING to see. And something like this COULD happen. If so, a trough with this trajectory and magnitude would be one of those that can bring 10-20 inches of rain in a DAY to southern California mountains, and, as shown later, continuing on at lower latitudes, bring a few inches in a day to the mountains of AZ! These are the kind of model outputs that make life truly worth living. A key ingredient here, too, is that trough that would bring extremely cold air down along the Pacific coast from Canada. That would help energize and deepen the surface low under the big trough offshore of southern Cal as it got closer to the coast. (Kind of reminiscent of what happened in Jan 1969, cold in the Pac NW, super rains in Cal, and maybe reminiscent of the weather configuration during the truly gargantuan Cal flood of late December-Jan of 1861-62 when 35 inches or so fell in 30 days in the Los Angeles area, which, in normal circumstances would have meant 70-100 inches during that time in the higher mountains! The LA Basin was a lake at that time, reports said. Does that much rain sound crazy for southern Cal? Well, the DAILY record Hoegee’s Camp Ivy, is 26.12 inches in ONE DAY, January 1943! More than 25 inches fell in one day in January 1969 before the gauge floated away. So, you COULD have 70 inches in only three days or so! Man, I am filled with historical facts today!
But does “spaghetti” support these exciting model outputs? I don’t know because I haven’t looked yet. But let’s do look at a couple and see if catastrophic, well, heavy anyway, rains are headed to Cal, and maybe AZ, too. The onset of this “break through” pattern begins in about nine days or so (exact timing will vary a bit):
Valid for about nine days from now, and shows a great beginning to the pattern discussed above. This says with pretty good confidence (judged by the bunching of the red contour lines) that the jet stream will break into Cal from the Pacific. The red lines bound the southern edge of the jet stream.
Moving ahead into the distant forecast future….(wow, this is getting to be too long again!):
Valid for 14 days from now. Note says it all.
Will look at this in a few days, noting that the ACTUAL model outputs will bounce around this “solution” but SHOULD tend to gravitate back toward it if it does bounce away from it (producing what would be considered an outlier).
Fun times in weather following ahead!
The End
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1Feel I have to ride that 0.40 inches rain prediction out since its “out there” and it was in the context of a friendly competition with a friend whose also big faculty member at a famous university in Fort Collins, CO, as well as a Catalina snowbird. In this regard, I have noted that some friends change their forecast with each model run, then in retrospect, select the forecast they made that was closest to the observed amount of the many they made, and then claim that they “really nailed” a rain prediction for Catalina.
Yesterday’s blog was re-written and re-organized some after finding several occasions of not such great writing and org.
