Haha, most readers won’t even notice! But maybe some cow-centric, instead of cloud-centric, folks will drop by, raising the worth of this blog to above $35 if sold….that according to a “biz” site.
Had a rainbow yesterday. Hope you noticed. It was pretty early and overhead west. I think the clouds did not have ice in them. The rain echoes were not showing up on the radar, suggesting the beam went over the tops. Sounding suggested tops might have been as cool as -5°C. In any case, the drops were able to tip the bucket a couple of more times, and along with yesterday afternoon’s brief, light rain showers our total has climbed to 0.37 inches for the storm. Not bad, though as in money, you always want more.
These storm breakup days are always our prettiest, and that’s often what this site is about, being pretty. Yesterday had some fabulous scenes; couldn’t stop shuttering cam. It is a real neurotic compulsive behavior pattern, as afflicts some of us cloud and storm-centric folk. Check Mr. Olbinsky’s work; his work goes beyond phenomenal whether you want a wedding photographer or want to see a storm chasing video. But it takes that kind of eccentric energy to be special, to stand out as he does.
Here, though, we let the storms and cloud scenes, such as they are, hope for the best, and let them come to us…. Kind of a lazy storm chaser’s attitude.
Still cold aloft, so having some nice Cumulus today is in the bag, the early Stratocumulus devolving into Cu, that is.
Honestly, I gave up on the chance of rain overnight into this morning at sunset yesterday due to the absolutely clear skies. And, like you, woke up to not one cloud within a 100 miles! How could this be, given the synoptic situation? Started slicing apples for some humble pie, but then, when looking at a radar and cloud loop (this one from IPS MeteoStar) saw that lower clouds had magically erupted to our west before midnight, and by the time they got here in the early morning hours, had little showers coming out of them!
I did not park my own dusty car out from the carport, either. I thought I would at LEAST see a pile of clouds on Ms. Lemmon, too, this morning! Sure wrong there. Here are a couple of images from what has to be considered a tiny weather miracle:
Chances of rain increasing (imagine!), for just over a week from now as actual model outputs begin reflecting what spaghetti (the many outputs) was indicating, i.e., a big upper trough in the West-Great Basin area. At the time that spaghetti was indicating that, the actual model outputs were not, indicating that they were outliers.
Check this out from last night. Since this model output is more in agreement with that crazy spaghetti plot, it inherently has more credibility, and is likely not an outlier model run. That what the NOAA spaghetti factory is used for, getting a handle on those runs that might be wild, and those that are more likely to verify.
Its valid on the morning of May 8th and shows a trough coming out of the Pacific ahead of the one from the Pac NW, shown at this time over northern Cal. The hope here would be that the one from the SW would have a generous amount of sub-tropical clouds with rain in them.
Cloud shots will be posted later this morning of the next day….. (i didn’t get to is as I had planned)
Yesterday afternoon, the 29th. Here’s what shallow, icy clouds look like, reflecting the unusually cold air above us.
PS: Chance of rain still holding for the 8th. See below for new depiction of big “cutoff” vortex over AZ from last evening’s model run:
Doesn’t look promising for much rain here in Catalina in March, however. No rain in sight through the next 10 days at least.
Let’s check our 7 inches with what’s happening upwind, say, in CALIFORNIA, and see if there’s been any drought relief there, through February, via the CNRFC:
As you are likely to know from many media stories last year, Cal was in a drought siege of five straight years, with but got a little relief last year in the northern part thanks to help from the giant Niño, one of the strongest ever.
Alas, it was one that failed to deliver as the big rain producer for the south half of Cal and the SW in general as was expected.
In case you’ve forgotten how bad things were in Cal, let us look back at what was being said, those horrific appearing drought maps, and also how hopeful were were at the time that the Big Niño would take a bit bite out of drought. This is a really good article:
Then, when the Big Niño faded away like maple syrup on a stack of buckwheat pancakes last spring and summer, we were surely doomed for more dry years. And, for a time, the dreaded cold tongue of water in the eastern equatorial region, the so-called, La Niña, started to develop, which would be no help at all for a good rain season like a Big Niño is, usually.
The Niña faded away, too, to nothing as the winter went on, so we really didn’t have much going on in the tropical Pacific to help us figure out what kind of winter rainfall regime we were going to have om 2016-17. Not having anything going on meant winter rainfall could go either way, a difficult to figure out situation for season forecasters.
In retrospect it is pretty astounding how big a signal must have been out there SOMEWHERE that this winter was going to be one for the history books on the West Coast in general, and in particular, for Californians. Californians saw their drought chewed up and spit out in a single winter, including snow packs so high the height of some mountain peaks have been revised. (I’m kidding.)
No one saw such an astounding winter coming.
This winter sure makes one think of the QBO (Quasi-biennenial Oscillation, one up there in the Stratosphere where there’s almost no air (haha, well, practically none)… Did the QBO have a role in this astounding winter; was there a delay in the effects of the Big Niño even without a bunch of convection in the eastern Pac tropics? Doesn’t seem that could be right…
But, William “Bill” Lau, U of Maryland scientist, reported some statistical evidence of such a lag way back in ’88 due to a QBO connection of some kind and ENSO, no physical cause could be discerned, however, not yet, anyway. Lau, 1988, is reprised below for readers who want to go deep:
Light rain showers overnight, just before midnight, and again just after 1 AM AST, raised our Sutherland Heights storm total to 0.33 inches, decent but disappointing in view of model and personal expectations (0.60 inches).
What was especially interesting is that those nighttime light showers didn’t show up on the TUS radar, suggesting very shallow tops, perhaps a “warm rain” event, one not having ice, or an “ice multiplication” event with tops warmer than -10° C, about where the tops were on the 5 PM AST TUS sounding.
By this morning, the tops were barely below freezing (about -3° C). Don’t expect to see ice today, except at Cirrus levels!
Last of the Cal rain blasters is making its way across the State today, with another 5-10 inches expected in favored Sierra and coastal ranges in the next 24-36 h. Numerous sites north of SFO have now logged over 100 inches since October 1st! Imagine. Great to see that Cal drought vanquished in a single year, so unexpected. Let’s hope the Oroville Dam, N of Sacto, holds.
PS: Using point and shoot cam now with “real” camera in the shop for awhile.
That’s why you come here, to answer important questions like that. After all, those precipitating clouds could have been Nimbostratus, Stratocumulus opacus praecipitatio, Cumulonimbus capillatus incus flammagenitus, or even just “plain” Cumulonimbus capillatus (no anvil), and possibly, Stratus opacus nebulosos praecipitatio.
Of course, with no large fires around, we can at once rule out Cumulonimbus capillatus incus flammagenitus….(the new name for clouds on top of fires, formerly referred to by the more accessible terms, “pyrocumulus” or “pyrocumulonimbus.”
For the curious, and since I broke my camera and don’t have the dozens upon dozens of photos to regale or bore you with, I will reach into the archives for a shot of “flammagenitus” and show you one from the pyromaniacs’ paradise, Brazil!:
Now, on to more recently viewed clouds, like yesterday’s:
Later these scenes were overtaken by a slab of Nimbostratus and steady light rain for a few hours.
A note on the recent southern Cal rain blast
As you know, up ten inches fell in some mountain locations in southern California as a monster low pressure system smashed into the coast near San Francisco1. You might recall, too, that the shift of the jet stream (and thus storm track) into the southern portions of California was well predicted two weeks in advance in those crazy spaghetti plots. You can’t always get much out of those plots except maybe the degree of uncertainty in weather patterns a couple of weeks out, but that was a rare case in which the signal far upstream for something strong barging into southern Cal also strong. And, of course, we are experiencing the residual of that storm, also as was indicated in those plots (“…the weather change around the 18th.”
Presently, a another sequence of extremely heavy rain is in the pipeline for central and northern California starting today, which will take a few days for it to come to an end.
Following a break, what was intriguing in the model outputs, and a little scary was that it appeared that yet another scoop of tropical air was going to jet across the Pacific under another blocking high in the Arctic and Gulf of Alaska into California. Take a look at this prog:
Here’s where spaghetti can shed some real light:
So while it is still possible that some model runs will indicate a blast from the sub-tropics affecting Cal, they can be pretty much waived off as outliers (not impossible “solutions” but rather unlikely ones. Breath easier Califs! At least after the current onslaught ends.
BTW, can you see what kind of weather is indicated in this plot for the SW and old Arizony?
Cold; temperatures below normal, precip likely at times.
——————————– 1The low pressure center that passed over San Francisco yesterday was not as deep (988 millibars) as the notorious “Frankenstormmaggedon” of 2010 which barged into Frisco with a 979 millibar center. You may recall, too, that spaghetti had strongly suggested a “Frankenstormaggedon”, as it was later called, also more than ten days in advance. Recall, too, if you can recall, that 2009-10 was an El Niño winter with this kind of thing pretty much anticipated.
For history buffs, I reprise that January 2010 storm as seen on our national weather map. You may recall that, if there’s anything left in that noggin up there, that Catalina experience no less than THREE inches of rain as this system went by, taking a couple of days:
I guess “billows” (“undulatus” in cloudspeak) two days ago in the late afternoon wasn’t enough of a sign that the weather was changing. Yesterday we had fast moving Cirrocumulus with rainbows in it, and as the sun was setting, “jet streak Cirrus”, a line of Cirrus clouds often seen in the very core of high altitude, powerful jet streams passed overhead.
How hard was the wind blowing up there in that Cirrus last evening? Oh, our Tuscon balloon sounding, lifting off around 3:30 PM, going up about a 1000 feet a minute to, indicates that the max wind up there at Cirrus level was 146 knots (just under 170 mph)! Yikes. Poor balloon. Must be in France by now.
The storm has been a bit of a disappointment in rain production. We’ve only logged 0.22 inches1. Not as much as foretold here, 0.33 inches, but that forecast was a better prediction than by “Weather Underground Robotics” (0.58 inches). Its great to beat a robot!
We had another sign yesterday in the fastest moving Cirrocumulus clouds I think you’ll ever see around here (about 100 mph), ones at just 18,000 feet above sea level, 15 kft above Catalina: rainbows of color near the sun called iridescence (also called “irisation”). Here, as is the norm here, are a few too many shots of the same thing2.
The colors themselves, of course, don’t warn of something about to happen, but the fast movement from the southwest did; a powerful jet stream is over you. That strong stream, the result of temperature gradients in the atmosphere, is dividing deep warm air from deep cold air, and steers the alternations of high and low pressure centers, and with those alternations of lows and highs along the jet stream, air is drawn from different latitude zones and the boundaries where those different masses of air meet at the surface, is called fronts. Here, such as last night, its nearly always cold ones.
The rest of the day was pretty exciting, the wind arising suddenly yesterday morning, along with our usual great visibility, and darker blue wintertime skies, made the clouds stand out more.
The sky at last, considering the power of the trough approaching, FINALLY began to fill in. Started looking around for the first sign of ice having formed in these clouds as the air aloft became cooler. Along with this filling in by Cumulus and Stratocumulus clouds, some sun highlights began to appear on our mountains, contrasted by the darkening skies above.
Eventually our jet streak Cirrus provided the background for another great sunset scene:
Today’s clouds and weather
From that map above, you’ll see that there’s a “tail-dragger” trough still to the west of us and about over Sandy Ego (haha). That’s going to keep the air over us extremely cold, and with some sun, the Cumulus clouds that arrive are expected to have tops colder than -15 to -20° C, plenty cold enough for the formation of ice.
Ice means precip, snow up there, rain down here in spots. So, we could still pick up a few more hundredths if a shower happens to drop by. The chance of isolated very light showers in the area is 100%, but no one can tell you if one will actually land on us. You’ll have to be watching, mostly after 12 noon. Look to the west toward the Tortolita Mountains, terrain that ought to spawn one or two of those.
Looks like a longer dry spell ahead; several days to a week, maybe more.
1CoCoRahs gauge, btw. NWS-style gauge had only 0.20 inches, likely due to enhanced wind loss associated with my collapsing prickly pear protector. 2 I was driving and had to park and jump out of car to get these. You only have seconds or maybe a minute or three to capture stuff like this.
In case you don’t believe me that over an inch fell, this digital record from Sutherland Heights with writing on it:
Probably a little more to come, too. Got some blow damage, I’m sure. Will be looking for roof shingles around the yard today.
And, as everyone knows from their favorite TEEVEE weatherperson, “New Storm to Pound SE Arizonans!” Begins Monday night, Tuesday AM. May have snow in it as it ends.
Your know, its no fun telling people what they already know, so lets look ahead beyond the normal forecast period of great accuracy, beyond not seven days, not eight, but beyond TEN days!
First, we set the stage with a ten day look ahead (from last evening) in a NOAA spaghetti factory plot:
This plot indicates that the pattern of a towering, storm-blocking ridge is certain along the West Coast by ten days–will be developing for a day or three before this, That ridge represents an extrusion of warm air aloft over the entire West Coast extending all the way into Alaska. The couple of red lines in and south of AZ are due to the change of a minor, likely dry, cutoff low in our area about this time (plus or minus a day).
In other words, this plot suggests a warmer, dry period develops over AZ, and storms are shunted from the Pacific Ocean, located west of the West Coast, all the way to Anchorage and vicinity, They will be welcoming a warm up in weather up thataway at some point in this pattern.
Is that it, then, for the AZ winter precip? It could happen. Just one more storm after the current one fades away today?
Hint: Sometimes anticyclone ridges like the one in the plot above get too big for their britches, and fall away, or, break off like a balloon from a tether, and a warm blob of air aloft sits at higher latitudes, often floating off to the northwest.
The exciting ramification of this latter scenario is that in the “soft underbelly” of the “blocking anticyclone” (as in American football), the jet stream throws something of a screen pass, goes underneath the belly of the blocking high, and races in toward the West Coast at lower latitudes. Having done so, such a break through pattern (“Break on through to the Other Side”) results in heavy rains in Cal and the Southwest.
Izzat what’s going to happen?
Let us look farther ahead, unprofessionally, really, and see if there is evidence in spaghetti for such a development and you already know that there must be because it would explain why I am writing so much here. Below, the EXCITING spaghetti plot strongly indicating break through flow breaking on through to the other side, i.e., the West Coast, from the lower latitudes of the Pacific:
Well, we’ll see in a coupla weeks if CMP knows what he is talking about.. I think this is going to happen, resembles what’s happening now, and weather patterns like to repeat, more so within the same winter. However, how much precip comes with this pattern will be determined by how much flow breaks on through to the other side….
Let us begin our look at yesterday’s clouds by looking back three days ago before the Big Storm. We had a nice sunrise. Here it is in case you missed it:
Moving forward to only two days ago, the day preceding the nighttime blast: a cold, windy day with low overcast skies all day, shallow, drizzle-producing clouds, something we don’t see a lot of here in Arizona.
By the end of the day, the clouds had lowered again, and we were about to have a very interesting night!
———————- 1Remember how great we hippie relics thought that first Doors album was? Later, the Doors, and that era were to be made fun of by 80s punk and humor group, The Dead Milkman in “Bitchin’ Comaro.” (Its worth a listen.)
Catalinans experienced a FOURTH cloudy day in a row, and, over the past few days, including yesterday’s few drops that fell at 4:24 PM, have experienced over an inch of rain!
Some grumbling has started concerning muddy, pot-holed and puddled up dirt roads, about the washes running across roads lately, water and mud splashing on the car day after day, and brutally low temperatures dipping to well below 50° degrees in the morning now for several days in a row. Its 40° F here as I write this.
While a brief respite is in progress now, Catalinans were discouraged to learn that more strong storms are due in this weekend, bringing possibly damaging winds and heavy rains that will augment the poor road conditions.
How much rain?
Let us look below and see how much has been calculated by our best model at the University of Arizona’s Wildcat Hydro and Atmos Sci Dept (I am so glad they provide this service; I donate to the Dept, as we all should!):
Hah! We can’t complain too much about inclement weather compared to California’s pluvialities. Here is a table and map of precip amounts for that State through just the first 14 days. Prepare to gasp:
The remarkable aspect of this rainfall anomaly on the West Coast and in the Southwest, which is also quite wet, is that it could not be seen in climate forecasts days to a couple of weeks in advance. Its not that the folks at the Climate Prediction Center aren’t the best that we can get, its just a statement about how hard it is to get a longer term forecast right. Many are right, but lately, recalling the “Big Niño Bust of 2015-16” where the forecasts of a wet Southwest and central and southern California went terribly awry, those forecasts have taken a beating. Here’s what was expected this winter by the CPC, first, for January, a forecast made on the last day of December. when the forecast models we use day to day would have had some influence:
As can be seen, the extreme rains that hit California, and our own well above normal precip, though on the doorstep on December 31st, were unforeseen. That’s how tough it is.
Below, the forecast for January through March, also going astray, though a recovery could be had by a very dry Feb and March in Cal and the Southwest, something not likely to happen now.
Glad I’m not forecasting for a month or three months! Gads, yesterday we had ice galore here and there, and I had predicted that morning that it was doubtful that ice could form in our clouds yeserday and how about that rainbow yesterday afternoon, to change the subject quickly, but smoothly; hardly a ripple, something gleaned from the election debates:
Some additional views, including a horse, which should increase web traffic:
OK, now for the rest of the day, your daily cloud diary:
But, then there were some great sun and lighting scenes in those showers, not to mention the brilliant rainbow that was to come:
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….
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:
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:
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.”
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:
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.
—————————– 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.
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.