One passed over at 9:19 AM with a hard multi-second, surprise rain shower. One person reported a couple of graupel, or soft hail particles. Tipped the bucket, too; 0.01 added to our Sutherland Heights storm total. Its now at 0.23 inches. Of course, there was no damage, but putting that word in a title might draw “damage trollers”, increase blog hits….
The rest of the day was clouds withering, getting mashed down on tops as bases rose and tops settled back, then suddenly, about 3:30 PM, small areas of ice crystals began to show up in a couple of spots, and, boy, did things take off after that. Tops were lifting to higher temperatures, likely due to an approaching trough, one that otherwise is too dry to do much else.
Honest to goodness cold, wintertime Cumulonimbus clouds formed, though not very deep ones. Probably of the order of 2-3 km thick is all (eyeball estimate).
But with our cold air aloft, tops were well below -20° C (4° F), lots of ice formed in them and produced streamers of ice and virga across the sky, and in tiny areas, the precip got to the ground.
And with “partly cloudy” conditions, there were lots of gorgeous, highlighted scenes around the mountains.
Let us review yesterday’s clouds and weather and not think about the future too much, starting with an afternoon balloon sounding temperature and dew point profile from IPS MeteoStar:
So what do clouds look like when they have tops as cold as -28°Ç?
Well, I really didn’t get a good profile shot of those clouds, they were either too close, obscured by other clouds, or too faraway, so instead let us look at two dogs looking at something as a distraction:
Well, let’s start this when the ice first appeared in a cloud, much later in time than what was thought here yesterday morning. If you logged this “first ice” you are worthy of a merit, a star on your baseball cap:
Well, while flawed from a cloud profile sense, here’s what they were looking at, it was the best I could do:
Let us go zooming:
Looking elsewhere, there are snow showers everywhere!
The day concluded with a very nice sunset:
Now, the long dry spell… Break through flow from the Pacific under the “blocking high” eventually happens about a week away now, but more and more looks like that flow might stay too far to the north of us, rather blast northern Cal some more, and not bring precip this far south. The blocking high needs to be in the Gulf of AK, but now is being foretold to be much farther north…
The End, gasping for air here. More like a treatise than a quick read!
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:
Later….drizzling Stratocumulus, same view:
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.
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.):
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.
A very few small, isolated drops fell between 4:50 and 5 PM here in Sutherland Heights from what appeared to be nothing overhead. You’d have to be really good to have not been driving, and to have anticipated the possibility (by recognizing ice in upwind clouds) and then having observed it. You would be recognized, given some extra adulation, at the next cloud maven junior meeting if you did observe it, that’s for sure.
So, a long blog about anticipating and observing a sprinkle of rain (RW—, “RW triple minus” in casual weatherspeak or text).
We start with some nice, but inapplicable to our main story photos from yesterday.
(What about those gorgeous Cumulus congestus and Cumulonimbus calvus clouds over toward and well beyond Charouleau Gap about this time? Maybe later or tomorrow.)
Some apocalyptic cloud scenes can be Cumulus that explode suddenly into Cumulonimbus, and Cumulonimbus clouds with their foreboding (unless you live in a desert) rain shafts, and their predecessor shelf clouds like “swirly dark Stratocumulus”, and arcus clouds, the latter, a lower line of clouds just above and a little behind the wind shift at the ground, usually just ahead of the main rain shaft. While we didn’t get to see an arcus cloud yesterday, we had some dramatic swlrly dark Stratocumulus clouds to scare us. I say “swirly” because if you looked up yesterday evening as they passed over, you would have seen rotation in them.
These can combine, as they did yesterday, to make you think someone might drop out of the clouds and fix the world1. See those scary photos below, way below as it turns out.
This monster collection of Cumulonimbus clouds (“mesoscale convective system” or MCS in weather lingo) with swirly shelf clouds preceding it barged over Catalina later yesterday afternoon after it appeared that not much was going to happen all day. Heck, there wasn’t even a decent Cumulus over the Catalinas until after 2 PM!
The result of this system slamming Catalina was the usual strong preceding winds roaring down from Charouleau Gap way and points north or northeast. The winds were not as damaging as three days earlier.
Then the rain! So nice! Got 0.55 inches of rain here in Sutherland Heights, an inch and half on Samaniego Ridge, and 1.65 inches on Ms. Lemmon.
Worth watching is the U of AZ weather departments time lapse video, especially beginning at 2 min 50 s into it. That’s when the big group of Cbs begins to make its presence known from the east. What is interesting, and what I have not seen before, is that you will see the tops of a thunderhead farther west, that icy part up around 30,000 to 40,000 feet, shoved backwards (back toward the west) by outflow at the tops of the huge incoming system. Very dramatic.
Detour: detecting ice in clouds….some practice shots
As the burgeoning cloud maven junior person you, of course, know how important the appearance of ice in our clouds is. You got ice; you got precipitation, which is snow up there, soft hail, hail, frozen drops.
Only the largest hailstones up there can make it to the ground as such here in Arizona due to our high summertime freezing levels. The rest melt into raindrops, some of which are large enough to reach the ground. Those downpours that suddenly emit from cloud bases were always hail or graupel (soft hail) aloft.
Sometimes in deep stratiform clouds attached to clusters of Cumulonimbus clouds, and with especially moist air from the base of the stratiform layer to the ground, clusters of ice crystals we call snowflakes make it to the ground without evaporating as steady light or very light rain.
Last night as our storm was coming to an end, it is likely that THOSE drops were once snowflakes rather than soft hail or graupel.
The End (finally)
1Huh. Maybe that wouldn’t be a bad thing. I am very concerned about microplastics (particles 5 millimeters and smaller) in our oceans, resulting from the breakup of larger plastic items we’ve been throwing in the oceans for decades. Seems those tiny particles are getting into everything, including the fish out there! It would be great if someone could get rid of them.
Lot of great scenes on the 18th, but, ultimately with hopes raised for appreciable measurable rain in Catalina, it was a disappointing day. Nice temperatures, though, for May if you’re a temperature person. Only a sprinkle fell (4:15 PM), and if you weren’t outside walking the dogs you would NEVER have noticed it.
Here is your full cloud day1, as presented by the University of Arizona Weather Department. Its pretty dramatic; lot of crossing winds, as you will see, and an almost volcanic eruption in the first Cumulonimbus cloud that developed near the Catalina Mountains.
That blow up was indicative of an remarkable amount of instability over us yesterday morning, one that allowed really thin and narrow clouds to climb thousands of feet upward without evaporating. Usually the air is dry enough above and around skinny clouds that even when its pretty moist, they can’t go very far without the drier air getting in and wrecking them (a process called, “entrainment”). Here are a few scenes from your cloud day yesterday.
More troughiness and winds ahead during the next week as has been foretold in our models, and reinforced by weather “spaghetti” plots, after our brief warm up today. No rain here, though. Seems now like rain can only occur at the very end of the month where weaker upper troughs coming out of the Pac appear to be able to reach down and fetch some tropical air.
1Its gone now because I couldn’t finish yesterday. Went off to Benson for horse training with Zeus.
I was really happy for everyone out there when the skies were dotted with so many perfect examples of Cumulus humilis. It was like a numismatist finding a perfect Indian head penny. If you were like me, and I suspect you are, you were just going CRAZY taking pictures of those flat little pancake clouds. Those clouds were pretty much limited to about 1,000 feet (300 m) thick at most
Not cold enough for ice in them, of course, since the temperatures at Cumulus cloud tops were only around -3 ° to -5 °C (28 ° to 23 ° F, respectively). Around here, ice USUALLY does not appear in clouds until the temperature is lower than -10 °C at cloud top.
Yesterday began with some light snow falling on Mt Lemmon…well, it was falling downward TOWARD Ms Lemmon, actually. Fell out of some thick Altocumulus clouds up there around where the cloud top temperature is… what? OK, silly question for you, probably lower than -15 °C (5 ° F).
Let’s check the sounding to be sure, remembering that the launch site (University of AZ) was downwind of air flowing from the NW yesterday that went over the Catalinas, so a sounding at the U of AZ might suggest higher temperatures than this cloud was actually at since the air was probably descending before it got there.
Indeed, as just seen by me, the TUS sounding indicates that layer, up around 14 kft above sea level, 11 kft or so above Catalina, not a city, but rather a Census Designated Place or CDP, was “only”at -10 ° C.
I reject that as the temperature of the virga-ing cloud over Ms. Lemmon! Its a little too warm IMO.
By afternoon, the skies over Catalinaland were spotted and dotted with spectacular Cumulis humilis examples. (The littlest shred clouds are Cumulus “fractus.”)
I’ve left the time of the photos off today. After all, there was only one true time yesterday, “perfect humilis time!” or as we like to say, “PHT.” Immerse yourself.
Yesterday was a great day both for airborne researchers studying the onset of ice in clouds, and for my followers to test their “ice” Q detecting abilities, to come up with a clever play on words there.
What was so great about yesterday’s clouds?
Well, they were real cold, bases up around 9,000 feet above Catalina (about 12,500 feet above sea level) at -7° C (19° F). Excellent. Nice data point.
This is what was pretty great for you and me; they didn’t overshoot much, the clouds were pretty flat, not very deep, not a lot of flight time needed climbing to cloud top to see what it was around here. That means that if you are flying around up there sampling clouds for ice content, that the tops you smashed with your aircraft were pretty much the ones at the temperature that the ice crystals you ran into later formed at. Remember, when cloud tops first rise up, they usually have little detectable ice (the ice crystals are too small for your instruments, or, they haven’t formed yet, takes a little time.
When there are big overshooting tops, an inexperienced, well, crummy researcher in an aircraft finding the ice, as it is usually found, lower down in the cloud, might put the origin of the ice at the temperature of the collapsed top, not at the lower temperature where it formed and the original top reached up to.
So, the lack of much overshooting made it a great day to assign the ice you found to the right cloud top temperatures.
What else was great?
It was a marginal day for ice formation here in the Catalina area, so you get a good data point on when ice starts to form in clouds given that base temperature. As the cloud deepens upward, more ice would be expected with the lower temperatures.
And, as noted by Ludlum way back in the 1950s, and by Prof. Battan right here at the University of Arizona which I did not attend, btw, that level at which ice and precip onsets changes from day to day (largely related to how warm (crazy isn’t it?) the cloud base temperature is. On days with warmer cloud bases, the ice onset temperature is also higher. For example, in summer here, its not unusual to have ice onset between temperatures of -5° and -10° C (23° and 14° F) when bases are warmer than about 10° C.
Anybody still out there?
So, yesterday, with the deepest Cumulus clouds around 2,000 to three thousand feet thick right in our area (they were deeper elsewhere), tops were running around -15° C, this temperature, as you know, leads to the formation of plate-like crystals, hexagonal plates, stellars (Christmas card crystals), maybe some spatial dendrites (stick out in different directions) if the latter crystals were in the Cumulus cloud long enough. If the concentrations of ice get high enough, you’ll get “snowflakes”, interlocking dendritic crystals. A single, good-sized snowflake might have 20-50 individual dendritic crystals.
Is anybody still out there?
Below some shots from yesterday afternoon when there were traces of ice spewing out of local clouds. Did you see those regions and note them in your cloud diaries, that’s the important question.
Stormy weather still ahead as noted here I don’t know how long ago. April looking more and more to be a generous month of rain here in Catalina. But will those showers be too late for May flowers?
When some of you were weather browsing this morning, and you saw this forecast map from IPS MeteoStar, valid for next Tuesday, which shows a very late in the season tropical storm off Baja heading toward the Southwest US, while a vigorous winter storm bashes the West Coast, I had a feeling that it reminded you immediately of one of your early weather memories of a similar situation. First, the IPS map.
The map below is from an era when you were a little child and maybe you, too, were clipping weather maps out of the Los Angeles Daily News, if that’s where you lived:
Looking back, but a little closer, like yesterday and the day before…..
Nice storm we just had. 0.65 inches fell in Sutherland Heights. Would not have predicted that much over these past couple of days to be honest. Total for month now 1.10 inches or a little above the 38 year average of 0.97 inches.
After a long dry spell though at least the next week, November will close out on a dry or wet note, which is pretty encouraging.
Yesterday’s clouds, ice and sun: a soliloquy on ice
Fair amount of ice yesterday in our low clouds. As you would guess on your way to becoming a cloud maven, bases AND tops were especially cold for AZ. Afternoon cloud bases were running about -8° to -9° C, whilst tops were about -15° C. Still ice was not plentiful. How’s come? Well, it seems the amount of ice in clouds is dependent on both the cloud top temperature and the droplet sizes in the coldest parts of the clouds (see Rangno and Hobbs 1994, Quarterly Journal of the Royal1 Meteorological Society) (Hell, no one’s going to read this, though it is now available without having to go through a “pay wall” and the page linked to above has been updated with new pdfs!)
In sum, a cloud with a base of -10° C and a top of -20° C will have LESS ice than a cloud with a base of 0° C with the same cloud top temperature (-20° C) because with a warmer base, the drops near the top of the cloud in second example will be larger.
That seems to be the way it works. So, yesterday’s thin cloud with cold bases had smallish drops, and ice production was a little limited.
Also, if you monitored Ms Lemmon, and the Catalinas in general, you probably were thinking, “Where’s the ice?”, in those cold Stratocumulus clouds as they piled up against them.
Well, when you have strong winds at cloud level as we did yesterday, and with ice crystals taking a little time to appear from some of the droplets that freeze in the cloud stream, grow, and eventually fall out, you’re not going to see much evidence of ice on the windward side of the mountains in these kinds of situations. The ice is going to appear and fallout as snow or virga downwind a good distance downwind, and that’s what was happening yesterday to nearly all of those deeper clouds (with slightly colder tops and larger cloud droplets in them) that formed over the Catalinas.
If you don’t believe me, yesterday’s time lapse movie from the our great weather resource, the University of Arizona, shows this. You’ll see a lot of precip and virga falling of those clouds as they stream eastward from the Catalinas. So, we didn’t get to SEE much ice from those Stratocu clouds but it was there.
Lastly, the sun, as it appeared yesterday at sunset in the dust-haze kicked up by that powerful low that brought us our rains. The jet stream, as was pointed out by a friend, was about 200 mph overhead of TUS at 40 kfeet. Wow.
1″Royal”–that is so funny; “hey”, guys, wake up, its the 21st century!
Looks like CMP is low AGAIN on his prediction! Thought a third was the most that could fall in our present storm chapter (10% chance of more, that is), and best estimate, 0.165 inches. Now it looks like met friend and professor at a major university will be much closer with his half an inch prediction. Very painful. Kind of like Stanford with their brainy team beating the Washington Huskies in fubball . It really hurts.
Let us begin today with a look at desert grasses from this summer and falls rains. Pretty deep, knee high in some areas, but as we know here, full of nettles. Kind of a cool look though.
Was heading out to see, what from Google Space, appeared to be a new meteor crater near me, one maybe the astro boys missed. Turned out it was just a house under construction, pretty much underground as well. Kind of a cool thought to build like this, lots of energy saved, which is always good. Cell phone service likely compromised.
…and a dense discussion of detecting ice in them. I am hoping that my followers noted the time of the first appearance of ice in those Cumulus and Stratocumulus clouds that began to fill in during the middle and late afternoon. As that happened, a few raindrops sputtered down here just after 3 PM as that happened. You should have logged both these events, the first visual appearance of ice, and when those drops fell in your weather diaries.
The whole point of this blog is the detection of ice in clouds by layman and laywomen, or “laypersons” I guess it should be now days. This is because if you see ice developing in lower clouds, something will be falling out of them soon. Ice grows in water clouds at below freezing temperatures at the expense of droplets. Therefore, if they stay in a water cloud long enough, they will get heavy enough to fall out. Poor droppies disappear, unless the air is really rising fast.
An interesting side note is that the air FLOWS THROUGH clouds, exiting on the downwind side. A cloud does not just float along as is. It is moving slower than the air, even itty bitty Cumulus clouds the cloudy air is being replaced constantly. The cloud is really moving upwind relative to the air! The POSITION of the cloud moves downwind, but SLOWER than the air that goes into it.
However, if ice crystals form in a small cloud then, they will fall out as single crystals at the downwind edge; they are not going to reach the ground unless you’re on a mountain top. You saw a fair amount of ice exiting the downwind end of clouds yesterday, falling out and evaporating in the dry air there. Where the cloud is wide, then they can gain some mass, collide with droplets, or other crystals and fall to the ground.
You need clusters of crystals locked together, called “aggregates” or ones that have gone through riming, collisions of ice crystals with drops at below freezing temperatures that freeze on the ice crystal making it more massive to get rain drops to the ground. Riming is what leads to graupel (soft hail) and hard hail (the latter to crystals impacting larger, often precipitation-sized drops that freeze on them).
For air travelers, or those who examine tree icing after storms, rime ice is white and produced by small cloud drops; clear icing is caused by much larger drops, usually drizzle or rain drop sizes. If the drops are too small (much less than about 20 microns) they are too small to hit anything and rather go around solid objects. Let’s say you’re on the top of Ms Mt Lemmon, say at 8.000 feet in the fog. The temperature is 24° F. Its windy. You look around and you see no icing on the pine trees trees up.
Where are you?
Ans: at cloud base.
That’s because itty-bitty drops, too small to hit on pine tree needles are flowing around the needles. Some great comments to make that would enhance your stature as a cloud maven junior is to offer your companion the information, “Wow, look at those trees! Here we are ing the freezing fog, and yet they have no ice sticking to them! That means the cloud droplets are pretty small, smaller than about 20 microns! I guess we’re at the base of this cloud system above us.”
These would be really great things for you to say. Of course, as you drove up to Mt. Lemmon, you would know already how far above cloud base you are, but, what the HECK.
You’re at Ms. Mt. Lemmon again, You like it up there when its in the fog. This time the temperature is 25 ° F. Its windy. The pine trees are loaded with rime icing, the ice juts out in the direction from which the wind is coming.
Where are you?
Answer: At LEAST a few hundred feet, more likely a thousand feet or more above cloud base. Drops have reached sizes above 20 microns in size, as they usually do at these heights above cloud base in old Azy. Later, you notice that the clouds are topping Sam (Samaniego) Ridge at the 6500 foot level. Now, they can’t be disconnected layer clouds, but rather SOLID from base to where you are. Drops are tiny again at the bottom of each layer.
Here’s another example. You get up in the morning after a cold winter storm to see “iced trees” on Ms Lemmon. Another comment you could be making is that, “Wow (always begin with “wow”), those clouds must have really been low based last night, way down on Sam Ridge!”
Riming on trees is analogous to the collection of fog droplets by trees and vegetation along the west coasts of the continents in onshore moving banks of Stratus and Stratocumulus clouds that intercept hillsides. These can be significant sources of water. Some studies of droplet collections by trees have found that under the tree, something like 20-40 inches of “rain” can be collected by a tree in northern California.
Wow, I can’t believe all the information I am providing today! Its really incredible.
“Just Another Day“, btw, one of the many great songs by Oingo Boingo, if you’ve ever heard of them. We’re not just about clouds here. Trying to broaden your pop cultural knowledge with distractions like this.
Yesterday was remarkable in how exact it was to the day before in clouds, but ultimately disappoiting.1 There was supposed to be more cloud action, shafting around, that kind of thing, but there wasn’t. It was virtually identical in every way, including having only two clouds that got high and cold enough to have ice in them. I am sure you recorded them in your cloud diary, and this will be a little tedious as a result, but….what the HECK.
Here is your cloud day for yesterday, focusing on the detection of ice in clouds:
Today is another day. More hope for a shower late today or tomorrow, models say, then likely another dry spell as the summer rain season ebbs again for awhile until that possible super hurricane Dolores drags some moisture up this way. (Dolores, now just a tropical storm, was just born off southern Mexico near the coast. Will be interesting to see just how strong she gets.
1Some fans like to see misspelled words here. Amyone see that criminal who was sentenced to “life in person” as described in the AZ Star? That was pretty grate.