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.)
What a nice steady rain with honest-to-goodness drizzle mixed in over the past two days. We’ve now had 4.24 inches in the past 30 days!
And yesterday, you saw the rarely captured on film, drizzly Stratus clouds, essentially something akin to wallpaper in the sky, but with misty visibility below its base. I hope you got a lot of photos of it; occurrences like that in Airizona1 its like finding a clean-shaven Lincoln penny.
And, of course, you knew that with misty, drizzly rain, clouds were shallow, no matter how dark they looked! Here’s the afternoon TUS sounding (from IPS MeteoStar) confirming that assertion2:
The drizzle likely fell from shallower parts of this cloud, while the accumulating rains, ones that “tip the bucket”, were likely associated with clouds all the way to that -10° C, where lots of ice would have formed. Drizzle occurrences and lots of ice in clouds at surprisingly high temperatures such as those tops we had yesterday are common, mutually inclusive observation in airborne studies of clouds then the tops go much below -4° C. But, its an unusual occurrence in AZ since we rarely have shallow clouds like yesterday’s with droplets in them large enough to form drizzle.
So, drizzle and what we call, “ice multiplication” occurring in our clouds yesterday made it a rare day, indeed for Arizonans to enjoy even if the mid-40s temperature all day was “less than optimum.”
Next up, more substantial rain after a couple of pretty nice, but maybe not thermally optimum days. Below, the latest output from the U of AZ supercomputing weather calculator showing the cumulative precipitation over the whole SW during the next week, starting from last evening. Quite fun to see the totals build up in that link above:
Being from southern Cal, what I find interesting is that another 10-15 inches of precip is forecast by this model’s output in the northern mountains of Cal, on top of the 20-30 inches they’ve already had JUST THIS MONTH!
Some cloud highlights
It pretty hard to top a photo like this one, so maybe I will just quit here. Wait to see what interesting clouds today brings for us. They’ll be shallow again as an inversion clamps down on the tops even a little more so than yesterday’s afternoon sounding shows, and the Stratocumulus and Cumulus clouds will be thinner, higher bases, lower tops, marginal for ice formation. So, not expecting to see ice in clouds today, but, then I wasn’t expecting so much rain, either from this little system that went through….
OK, one more:
————————— 1Misspelled on purpose to emphasize the quality of the air we have in Arizona, at least yesterday. Chamber of Commerce, are you listening? “Airizona,” as our new State name, would work great to attract people from smog-laden regions. I’m sure! Hmmm, or maybe just a good, new athletic shoe would do it, “Nike Airizona”… Nike, are you listening? 2One of the great moments in a life, as we all know from time to time, is in confirming an assertion, which also might be accompanied by gloating.
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.
Former Hurricane ‘Newt’ brought some real humidity, low clouds with unusually warm bases (around 15-20 ° C) to Tucson and Catalina yesterday as its remnant center passed just about over us.
Old Newt was “dragging” here as a tropical storm, aloft it was pretty strong still, brought near hurricane force winds on isolated, high, mountain tops. Mt. Hopkins reached 59 kts from the ESE before the “eye” passed nearby and the winds turned to the west. And in the Rincon Mountains a gigantic 6.39 inches was logged, and a site on Mt. Graham reported 6.43 inches. (Thanks to Mark Albright for these reports.)
While Sutherland Heights received only 0.29 inches in that all day rain, there were eye-popping totals in the Catalinas. Take a look at some of these, Dan Saddle near Oracle Ridge, nearing 6 inches in 24 h! Below, 24 h totals ending at 2 AM this morning, which pretty much covers Newt:
Horseshoe Bend Rd in Saddlebrooke
Oracle Ranger Stati
approximately 0.5 mi SW of Oracle
Edwin Rd 1.3 mi E of Lago Del Oro Parkway
approximately 1.5 mi W of Charouleau Gap
approximately 1.1 mi NE of Charouleau Gap
NE corner of Catalina State Park
CDO @ Rancho Solano
Cañada Del Oro Wash NE of Saddlebrooke
CDO @ Golder Rd
Cañada Del Oro Wash at Golder Ranch Rd
Oracle Ridge, approximately 1.5 mi N of Rice Peak
CDO @ Coronado Camp
Cañada Del Oro Wash 0.3 mi S of Coronado Camp
Samaniego Peak on Samaniego Ridge
Dan Saddle on Oracle Ridge
Catalina Hwy 0.8 mi W of Palisade Ranger Station
Sabino Creek 0.6 mi SSE of Marshall Gulch
Your cloud day yesterday; we don’t talk about today. That’s for tomorrow.
The day began with one of the great examples of Nimbostratus, that technically a middle -level cloud greeted us at daybreak in what was one of the great examples of the phantom cloud, the true precipitator, usually hidden from view by lower clouds such as Stratocumulus. But, yesterday morning, there it was, “Ns” naked as could be. I know many of you have been looking for a good shot of Nimbostratus to add to your cloud collection for a long time and I could feel the joy out there when I saw it myself. I only took a couple of shots myself, wish now I had taken more of an extraordinary scene.
Then, as the light rain here moistened the air hour after hour, low clouds, such as Stratocumulus and Stratus fractus began to form along the mountains, producing some interesting “tracers” of the chaotic air movement over there by the Catalinas under nearly calm conditions. Newt disappointed in his wind accompaniment.
Later in the day, as the highest, coldest cloud tops associated with those beautiful Nimbostatus clouds moved off to the NE, and our cloudscape became a mix of deeper Stratocumulus with Cumulus and isolated Cumulonimbus cells, they produced true drizzle and misty, visibility-reducing “warm rain”, that rare type of rain that falls here from clouds lacking in ice, began to be observed producing Hawaiian looking rain on our mountains, delicate shafts of rain whose small drops slanted away from the base.
Here, you might well erupt with, “This doesn’t look like Hawaii, but Ocean Shores, Washington, or some other coastal location along the West Coast on a spring day having Stratocumulus with drizzle!”
You would be correct in that eruption.
Below, an example of drizzle drops on your car’s windshield:
Later, it was to look little more “Hawaiian”, but if you’ve been to Hilo, you know its mostly cloudy all day.
“Warm rain” or rain due to the colllision-coalescence process, is also mainly associated with “clean” conditions, ones low in aerosol particles that can act as cloud condensation nuclei. The fewer the “CCN” the fewer are the droplets in clouds, and the larger the individual cloud droplets are when saturation and cloud formation occur. So, by yesterday afternoon, certainly, it was doggone clean here, no doubt aided by washout in that light rain we had.
Particularly heavy rain with low visibility fell just south of Catalina yesterday afternoon around Ina and Oracle just after 4 pm. However, that rain did not have those HUGE drops that we see from unloading, deep, Cumulonimbus clouds making this observer think as heavy as it was, it may have been due to a Cumulonimbus topping out at less than 20,000 feet, where the temperature would have been too warm for ice. The 500 mb temperature yesterday was a tropical-like -3.7° C on the TUS sounding, almost unheard of with a rain situation here. This, another sign of tropical Newt, since tropical storms/hurricanes have warm cores.
lacking in those huge drops we see in our thunderstorms, this rain likely formed from the “warm rain” process except maybe in the very heaviest rain areas. It was a special day.
You probably noticed how quiet it was; no thunder around, for one thing, indicating the updrafts in the clouds were not very strong, and that was another indicator that the clouds may not have contained ice. Without ice, hail and graupel, soft hail, you don’t have lightning.
The lack of lighting, the all day off and on rain, such as you might experience at Hilo, Hawaii, on the windward side, made it seem like you were in Hilo, Hawaii, or one of the other wet spots on the windward side of the Island.
The “perfect storm”? Well, maybe the perfect rain, and it kept giving fro several hours yesterday after our best model said it should end yesterday before 11 AM. And what a nice rain! 1.18 inches total here in Sutherland Heights, as measured by a CoCoRahs plastic 4 inch gauge. (You might consider getting one, btw, or one from the U of A’s rainlog.org)
Went down to the CDO and Sutherland Washes to see what was up after seeing the gargantuan 4.96 inch total on Ms. Lemmon, and the 3.62 inches at the Samaniego Peak gauge. Below is the resul for the Sutherland, both were the same, nary a drop in them:
The weather WAY ahead, too far ahead to even speculate about:
NOAA spaghetti plots still suggesting a pretty good chance of rain here around the 23-25th of this month. Nothing before then.
Yesterday, in the wake of TD Odile, it was about as Hawaiian a day in Arizona as you are ever likely to see. First, the high dewpoints, ones that replicate those in HI, mid and upper 60s (69-70 F in HNL right now), cloud base temperatures of around 60 F, and with misty, even drizzly warm rain around at times. The only thing we didn’t see was a rainbow, so common in HI they named a sports team after them.
If you thought the clouds looked especially soft-looking yesterday, I thought they were, too. That soft look that also characterizes clouds in Hawaii and other pristine oceanic areas arises from low droplet concentrations (50-100 per cc), characteristic of Hawaiian clouds.1 Both low updraft speeds at cloud base, and clean air result in low droplet concentrations in clouds.
The result of these factors?
The droplets in the clouds are larger than they would be forming in air with more aerosols (having “cloud condensation nuclei”, or CCN) and stronger updrafts at cloud base. Yesterday, you could have remarked to your neighbors late yesterday morning, as the rain and true drizzle began to fall from that Stratocumulus deck out to the SW-W, that the droplets in those clouds, “….must’ve exceeded Hocking’s threshold” of around 38 microns diameter. Lab experiments have demonstrated that when droplets get to be that large, which isn’t that large at all, really, that they often stick together to form a larger droplet, which in turns, falls faster and bumps into more droplets, and collects them until the original droplet is the size of a drizzle (200-500 microns in diameter) or raindrop (greater than 500 microns in diameter) and can fall out the bottom of the cloud.2
Mods still coming up with cold snap at the end of the month, even with rain as the cold front goes by. How nice would that be to finish off September? Still have a couple of days of King Cumulonimbus around as tropical air continues to hang out in SE Arizona. Hope trough now along Cal coast can generate a whopper here before that tropical air leaves us. Am expecting one, anyway, in one of the next two days, probably our last chances for summer-style rain.
Speaking of Odile….
the thought that inches of rain might fall in Tucson, something we all heard about two eveings ago WAS warranted by the gigantic amounts that occurred as Odile slimed its way across extreme southeast AZ. In modeling terms, the error in its track was pretty slight, but the predicted amounts that we COULD have gotten were pretty darn accurate. I did not see these amounts until after writing to you yesterday. Note those several four inch plus values around Bisbee, and the one in the lee of the Chiricahuas. That one 4.45 inches over there suggests to me that the Chiricahuas like got 4-6 inches. Check’em out:
———————— 1Except those affected by Kilauea’s “VOG” which have much higher concentrations, and look a little “dirty.”
2A thousand microns is a millimeter, in case you’ve forgotten, and that’s only about 0.04 inches in diameter. Most raindrops are in the 1000 to 3000 micron diameter range, though the largest, measured in Brazil, the Marshall and Hawaiian Islands, can be about a centimeter in diameter.
Yesterday was equal to the most potent cloud day that cloud maven person has seen since moving to Catalina in 2008; from clear skies to thunder before 10 AM! Fortunately, in spite of all the incredible cloud scenes around, fine, tall clouds so early in the day, CMP was able to control himself and only take 190 photos yesterday, and will share only a 100 of the best with you.
Kind of lost interest, though, when the sky went gray in Altostratus opacus cumulonimbogenitus after about 3 PM. Didn’t get any rain here, either, which was a disappointment.
Oh, well, “Today is another day”, to paraphrase Scarlet O. And another chance for an isolated TSTM to land on us.
Saw some of the most intense rainshafts that you can see here, likely producing 1.5 to 3 inches over there on the Tort Mountains around 2 PM and thereafter yesterday. Thunder was continuous from it for awhile.
But, in poor little Catalina, not even a drop. Even though Altostratus opacus cumulonimbogenitus (copied and pasted that linguistic monstrosity to keep things moving) did not rain here, there were a few drops that got to the ground from it around James Kreig Park where CMP taking batting practice for some reason with a friend. The balls were winning.
In spite of the boring cloud scene in mid-late afternoon in Altostratus opacus cumulonimbogenitus, the skies were open far to the west and allowed a sunset display that was pretty much unequaled in CMPs experience anywhere. So, though it didn’t rain here, we got a nice light show. Hope you saw it. Go to the end to skip a lot of excess verbage and less interesting photos.
The end of the day, BTW, was ruined when a TEEVEE meteorologist came on during a local news program told his viewers that “drizzle” was falling somewhere in the area. My faced turned red, I clinched my fist, and pounded the dining room table, veins standing out. This is exactly why I don’t watch TEEVEE. Under my watch, he’d have been fired before he got off his next sentence off.
But that’s me, CMP, a person who cares deeply about educational standards. As a public service, once again I begin this blog with a photo of what’s not “drizzle”, its that important. Remember that guy (actually, a world famous prof) I told you about that asked me to leave his office and never come back right after CMP told him that it had been drizzling outside? Q. E. D. (The occurrence of drizzle meant that all of that professor’s peer-reviewed body of work in clouds was in error. OK. enough past interesting personal history… Well, maybe this; told him there was a lot more ice in his clouds than he was reporting before the drizzle comment. You could see why that prof might be “concerned.”
Drizzle, of course, is fine, CLOSE TOGETHER drops smaller than 500 microns in diameter (0.02 inches!) that almost float in the air. You can get really wet biking in drizzle, and forget about a baseball cap keeping those drops off your glasses. They can barely fall out of a cloud; you have to be real close to the base to even experience them and that’s why drizzle is commonly experienced falling from very low-based clouds along coast lines.
You can tell how much that erroneous report of “drizzle” falling in Tucson affected me in how I am starting this blog with an educational soliloquy instead of jumping into cloud photos.
By now, you’d probably like to skip to the chase, and going to the U of AZ time lapse is a good way to do that. Unfortunately, as the storm hit the campus, the power went out for a couple of hours and you miss a good part of it and end of skipping from the middle of the storm to, let’s hear it, “Altostratus opacus cumulonimbogenitus.” Its great when you can say big terms like that; it’ll make you sound more educated than you probably are!
OK, after LONG diversionary material, a sampling of yesterday’s fabulous clouds, so many will post them as thumbnails so’s I can cram in more, and, that glorious sunset, too:
And we might even end up with TWO inches total for this storm! Amazing! I couldn’t imagine it, even as a precipophile with a known bias, that more than 1.5 inches would fall from this situation (10% chance of more than that I wrote), with a best guess of only about an inch.
Even the mods grossly underestimated the amount of rain that would fall during the day yesterday, and THAT was the huge surprise in this situation, with several inches falling in the Cat Mountains in the first 18 hours. It appeared in the models that the major rains would occur overnight and this morning, rather than during the day yesterday.
Three to five inches of rain have fallen in the Catalina Mountains since the storm began about 36 hours ago. Is the CDO flowing? Sutherland Wash? Streamflow reports for the CDO don’t show anything at this hour, surprisingly.
We’re now in the main cloud and rain band wrapping around the upper low near San Diego and more showers, maybe a roll of thunder, will continue through this evening. This band was supposed to be the major rain producer, in the mods, but likely won’t now, though won’t be as great a rain producer as yesterday. Probably a tenth to half an inch likely during the day as the band continues over us for another few hours. And here is your U of AZ mod rain forecast, hour by hour.
While not forecast in this U of AZ mod run, sometimes secondary bands develop separate from, and behind the main one we’re now in, and I think there is a pretty good chance of that happening today. Often, there’s a nice sunbreak as the main band departs and before the second separate one comes through, so watch out for that possible surprise in case you think the storm is over.
Pity the poor Oregon Donald DuckTM football team, playing in “Eugene weather” against the Cats today in Tucson, Arizona. Imagine what they expected the weather to be here even a week or two ago! And those poor Tour de Tucson bicyclers, too, peddling around flooded streets!
Upper low passes overhead later in the day tomorrow, which means a day with the coldest air will be over us then, and with that, we’ll have some great looking Cumulus and small Cumulonimbus clouds, scattered showers, maybe enough depth for some graupel and lightning before the weather dries out again for a few days.
Sometimes in these situations like we have today, dramatic line of showers/thundershowers with a fronting arcus cloud can develop to the west and southwest and roll across Marana and Oro Valley in the afternoon. Will be looking for something exciting like that today.
Coming up, another forecasting conundrum….
While the US model has a trough passing over Cal as November closes, while the GEM Canada has the SAME trough offshore of Baja at the same time, a huge dispersion in model results we don’t see very often when they start with the SAME global data and its only five or six days away!
Recall the USA model was in error for the current storm early on, showing it to come inland and be rather dry when the Canadians came up first with a monster using that same global data. So, leaning toward the Canadian model this time around; that the incoming low at the end of the month has a good potential to produce more rain here by having a more offshore and southerly trajectory before arriving.
Below, the Canadian solution, and below that, the USA one, FYI as an example about what weather forecasters have to deal with sometimes:
Yesterday, too, after the light to moderate rain in the morning, was a rare episode of Arizona drizzle. I am sure the best of the CMJs noted this. And what does it tell you? The clouds overhead are exceptionally “clean”, droplet concentrations are LOW, likely less than 150 per cubic centimeter, or 150,000 per liter, which we consider low, though it probably sounds high to normal people.
The aerosols on which cloud droplets form on, called “cloud condensation nuclei”, or CCN, got pretty much wiped out by rain, as you would guess yesterday, and so air involved in cloud formation hasn’t got a lot of CCN available. Normally in inland areas, clouds with 300, 000 to a million droplets per liter are common.
When droplets are few, the water that condenses in the cloud is dispersed on fewer drops, and so each drop tends to be larger than in polluted clouds. When they are larger, and reach diameters of 30-40 microns (about half or so of a human hair) they can collide and stick together, form a much larger droplet that falls faster and collides with more and more droplets until it falls out of the cloud. In this case, because its a thin Stratus cloud, the droplet only can grow to drizzle size, one by definition that is smaller than 500 microns in diameter (about five human hair widths. They don’t or BARELY make a disturbance in a puddle. So, when you saw those drizzle drops falling out, you KNEW that the largest droplets in that shallow Stratus cloud overhead had attained 30-40 microns in diameter.
Some rare drizzle precip1 fell yesterday. Suggests clouds were pretty “clean”, that is, didn’t have much aerosol loading and the concentrations of droplets in them was low (likely less than 100 cm-3) Also likely, in view of the recent strong winds, some of the aerosols in those clouds might have been large dust particles2 rather than those due to just “smog” and other tiny natural aerosols. Large dust particles can not only influence the development of ice at higher temperatures than normal (above -10 C), but is also known to aid the formation of rain due to cloud drops bumping into each other and sticking together; collisions and coalescence because large dust particles can accelerate this process by forming large initial drops at the bottom of the cloud where drops first condense. Here, drops are nearly always too small to bump together and join up unless clouds are deep, like our summer ones, and ice is going to form anyway.
So, yesterday, was a bit of a novelty. Some photos and story telling:
Mods paint dry weather for the next 15 days, and so yesterday’s disappointing “trace” (don’t recall here that Mr. Cloud Maven person had predicted at least 0.02 inches!) may be it for October. Phooey.
1Drizzle: Fine (size range, 200-500 microns in diameter drops) close together, that nearly float in the air. Very difficult to bicycle in drizzle even with a cap or big hat. Fallspeeds, just a few mph. Smaller sizes can’t make it out of the cloud, or evaporate within a few feet almost if they do. Even true drizzle occurrences, you can’t be too far below the base of the clouds or those tiny drops won’t make it down to you.
2What is a “large” dust particle in a cloud? Oh, 1-10 microns in diameter, real rocks compared with the other stuff normally in them. So’s you get a drop that’s already pretty large as soon as condensation takes places. And, if the updrafts are weak at the bottom, then only them big ones might be activated, keeping the whole cloud’s droplet concentrations low! Happens even in places in the middle of huge land masses where in Riyadh, Saudi Arabia, we saw this happen on a dusty, moist day in shallow Stratocumulus clouds. They developed some drizzle drops. I was with the National Center for Atmos. Research on a field project then.
31988: Rain from Clouds with Tops Warmer than -10 C in Israel (Quart. J. Roy. Meteor. Soc.)
Yesterday, that is. It felt like I never left. Only 49 F here; was 55 F in Seattle yesterday.
But the main thing that made it seem “so Seattle” was the persistent low Stratocumulus overcast, almost no sun whatsoever, and a little rain. We picked up another 0.03 inches in a couple of morning episodes of R– (an old weather texting1 shorthand for “very light rain”) to bring the storm total here to 0.55 inches. Of course, the best part of that overcast was that it allowed the ground to be damp for another day, helping the spring grasses and wildflowers by keeping the soil moisture in the soil and not flying away under a hot sun. The worst part of the overcast that lasted almost all day, was that Mr. Cloud Maven person had the day completely wrong–thought it would break open in the afternoon to “partly cloudy” and so he was as gloomy as the sky. You see, as a weather forecaster, you can’t even really enjoy a nice day if you didn’t predict it. Had some sad 75 F days in Seattle when I only predicted 69 F; everybody having summer fun but me.
Enough nostalgia, here are the clouds, even if you have no interest in seeing such boring clouds again:
Some residual small Cumulus, maybe clumping into a larger group this morning for a bit, which you would then refer to as Stratocumulus. Should gradually diminish in size and coverage until almost completely clear in the afternoon. Expect a north wind in the afternoon, too.
The weather ahead
There isn’t any, well, not right away, but WAY ahead….
Chances for rain begin to pick up after the 19th as we enter the “zone of curl”, “cyclonic curls” in the upper atmosphere with a lot of “vorticity” in them again, with temperatures falling back to normal values. Pretty tough to have warm weather for long at this time of year in AZ. You see, its troughs like to “nest in the West” in March, April, and May, even when they’re not strong and far enough south to bring rain, maybe only wind. Its a climo thing, and it causes many areas of the West to see an increase in precipitation in March from February, and also halts the rapid rise in spring temperatures (especially in Seattle, hahahaha, sort of).
This because the global circulation pattern, responding to the climb of the sun in the sky and warming continents in the northern hemisphere, those forces acting on the position of the jet stream, and weakening it here in the NH (northern hemisphere), is changing the jet stream pattern so that storms begin to move southeastward from the north Pacific across the Pac NW into the Great Basin area in the spring, bringing cold north Pacific air into the West. There was a great report about this phenomenon by old man Bjerknes out of UCLA with his Ph. D. grad student, Chuck Pyke, back in the mid-1960s. Pyke was a UCLA sports nut, BTW, to add some color to this account.
We won’t see that “trough in the West” pattern for awhile here in our “oasis of warmth” now about to begin, but count on it returning, as it appears to do late in the model runs from last night. Climo is forcing it.
The End, except for footnotes.
——————————————- 1Yeah, that’s right. Weathermen, as we would say it then, were way ahead of their time, “texting” each other long before kids thought of “texting.” You might write a weather friend, if you could find one: “We had a TSTM to the S with FQTLTGCCCG ALQDS last night for a few H. MVD N.” PIREPS, SIGMETS, too, were all “texted” and texted by teletype! Tell your kids.
2Was under the aegis of Research Applications Program (RAP) at the National Center for Atmospheric Research (NCAR) in Boulder, CO. Money was good…though not nearly as much as you would make as a TEEVEE weather presenter (hahaha). I was a post retiree guest scientist for RAP NCAR. Clouds could be real bumpy there in Saudi, thought I was gonna die once as bottom dropped out of the Lear going into Cumulonimbus at night that one time. Pilot liked to cut it close between the hail shafts and the rising parts of the Cu with little or no precip, using his aircraft radar. But sometimes, it was a little too close…and we got into the shear zone between a strong updraft and the downdraft.
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