Yesterday was as rare a day in Catalina, Arizona as seeing the marbled murrelet in Olympia, Washington.1
Our bit of rain (0.12 inches in Sutherland Heights) was only due to that formed by the collision-coalesence process, some times called the “warm rain” process, or more technically, non-brightband rain2.
No ice needed.
Usually clouds at inland locations like Arizona have so many droplets in them , a few hundred thousand per liter or more, larger drops that can collide and coalesce don’t form because the condensed water is spread over so many of them.
So I could feel the excitement out there as that frontal band got closer. Perhaps you saw the drizzle-mist rainbow on the Tortalitas, looked at cloud tops, and saw no ice. If you said you saw some ice yesterday you were mistaken or lying to impress your friends.
Let us review yesterday in clouds:
Skipping a LOT of pretty scenes now…..
Valid for 10 AM, yesterday. Output was from the 11 PM AST model run, a diagram with a lot of writing on it.
The rest of the day was overcast, cool with a period of light rain around 2 PM, with the temperature dropping to a remarkable 58° F here in Catalina.
The last TUS sounding seemed to confirm this unusual rain day, indicating that the stratiform tops near and over the site were at 0° C.
Our final rain total in Sutherland Heights was a respectable 0.12 inches from a rarely observed event. 0.47 inches fell on Ms. Lemmon for the highest amount around.
Might add more later, but am quitting now to go “lunge” and ride a horse..
PS: I have added more, re-written some not so great “formulations”…
1If upon reading that sentence you would like bail on reading about clouds and rain here in Arizona and read about that bird, please consult:
2When steady rain is occurring, returns have a bright band, or a augmented return from the layer in the atmosphere where snow is melting into rain. On days like yesterday, throughout the Tropics, along the West Coast, among many places, non-brightband rain is fairly common. Typically it falls from clouds with tops warmer than -5° C. Ice usually onsets at temperatures between -5° and -10° C in such clouds. Hawaii is a good example where “warm rain” produces most of the prodigious rain totals there on the windward slopes, such as that at Mt Waialeale on the Island of Kuwai where the average rainfall is more than 450 inches!
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.
The sky was packed with tropical Cumulus congestus and a few Cumulonimbus clouds in the distance at dawn yesterday, an unusual sight for Catlanders. A few of those Cu around the Catalina/Saddlebrooke/Oro Valley area grew overhead into “soft-serve” Cumulonimbus clouds with heavy, tropical-feeling showers you could hike in with great comfort; no lightning/thunder observed.
Up to an inch likely fell out of the core of the largest ones yesterday morning, but only .09 inches was recorded here in the Sutherland Heights. The Golder Ranch Drive bridge at Lago del Oro got 0.28 inches, Horseshoe Bend in Saddlebrooke near one core got 0.71 inches, Oracle, a half inch. Due to the exceptionally warm cloud bases, about 60 F again, warm-rain processes were certainly involved with those showers, though glaciated tops were usually seen, too. In warm base situations, they can act together.
Now here’s something interesting of me to pass along to you, something you might want to pass along to your friends when the opportunity arises: ice doesn’t seem to make much difference in the rainfall rates of true tropical clouds in pristine areas, only a little “juicier” than the ones that we had yesterday. Early radar studies in the 1960s1 indicated that the rainrates of tropical clouds peak out BEFORE the cloud tops reached much below freezing, a finding that has been confirmed in some aircraft studies of rainrates in tropical clouds2. Icy tops going to 30 thousand or more really didn’t do much but add fluff. All that really heavy rain that developed before the cloud tops reached the freezing level was just due to collisions with coalescence (AKA here, but nowhere else because its too silly, as “coalision.”) So, “coalision” can be an extremely powerful and efficient way to get the water out of clouds and onto the ground!
Scattered storms beautified the sky the whole day in the area. More are expected today, as you likely know. Have camera ready! Hope you get shafted!
Cool snap, maybe with rain, virtually guaranteed now for about the 26th-27th. Should make a good dent in the fly season, if you got horses and have been battling them all summer you’ll really welcome this.
Your Cloud Diary for September 19, 2014.
We start with an early morning vignette, down there somewhere:
Vignette: When this cloud bank above Sutherland Heights (shown above) darkened up, looked more organized, and with Cumulonimbus tops visible and showers already nearby, I made the not-so-surprising comment to two hikers about to leave on their hike hour long hike, “Watch out for these clouds overhead!”
They got shafted, see photo below; came back soaked, their dogs, too.
But, I had done my best. True, it was early morning, and after all, those hikers were likely thinking, “it doesn’t rain much here in Catalina in the early morning” (unless its FOUR inches like two weeks ago).
Cloud of the Day:
The End, enjoy our last couple days, it would seem, of our summer thunderstorm season. Oh, me.
1Saunders, R. M., 1965; J. Atmos. Sci.
2Cloud Maven Person with Hobbs, 2005, Quart; J. Roy. Met, Soc.
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.
Odile passed to the S and E of Cat land, leaving only 0.13 inches here in the Heights, the Sutherland ones. Didn’t even get the half inch I hoped for. Oh, well, we can be happy for the droughty areas of New Mexico that got the brunt of that tropical system as did portions of extreme SE AZ. You may know that for many days in advance and up until 11 PM the night before last (shown here), our best models had O practically passing right over us with prodigious rains indicated.
Unfortunately, we meteorologists often “go down with the ship” when this happens due to model forecast consistency. Only in the last minutes, so to speak, did the model runs get it right (but too late to be of much use) and finally indicated that the true path of the heaviest rain was NOT going to be over us, as was already being discovered via obs. O was such a cloud mess, the mods may have been off in locating where the center was. Not sure. Will have to wait for the panel report.
Seems to be preciping on the Cat Mountains right now, though doesn’t show up on radar, so its likely a RARE “warm rain” event here in AZ where the rain forms by collisions between larger cloud drops to form rain drops and the cloud tops are low1. Maybe that’s O’s legacy; tropical air and a warm rain day sighting.
BTW, whilst Catalina and most of Tucson didn’t get much, it has continued to rain steadily in our mountains over the past 24 h with Dan Saddle, up there in the CDO watershed, leading the way with 2.09 inches in 24 at this hour (5 AM) and its still coming down lightly, as noted. Its been a fantastic rain since it was steady and soaking up there over that whole 24 h period, much like in our winter storms. Below, some totals from the PIma County ALERT gauges. You can see more totals here.
Gauge 15 1 3 6 24 Name Location ID# minutes hour hours hours hours —- —- —- —- —- —- —————– ——————— Catalina Area 1010 0.00 0.00 0.00 0.00 0.16 Golder Ranch Horseshoe Bend Rd in Saddlebrooke 1020 0.00 0.04 0.04 0.04 0.20 Oracle Ranger Stati approximately 0.5 mi SW of Oracle 1040 0.00 0.00 0.00 0.00 0.12 Dodge Tank Edwin Rd 1.3 mi E of Lago Del Oro Parkway 1050 0.00 0.00 0.00 0.00 0.16 Cherry Spring approximately 1.5 mi W of Charouleau Gap 1060 0.00 0.00 0.00 0.00 0.16 Pig Spring approximately 1.1 mi NE of Charouleau Gap 1070 0.00 0.00 0.00 0.00 0.04 Cargodera Canyon NE corner of Catalina State Park 1080 0.00 0.00 0.00 0.00 0.20 CDO @ Rancho Solano Cañada Del Oro Wash NE of Saddlebrooke 1100 0.00 0.00 0.00 0.00 0.08 CDO @ Golder Rd Cañada Del Oro Wash at Golder Ranch Rd
Santa Catalina Mountains 1030 0.00 0.04 0.04 0.08 1.73 Oracle Ridge Oracle Ridge, approximately 1.5 mi N of Rice Peak 1090 0.00 0.00 0.04 0.04 0.75 Mt. Lemmon Mount Lemmon 1110 0.00 0.00 0.00 0.00 0.43 CDO @ Coronado Camp Cañada Del Oro Wash 0.3 mi S of Coronado Camp 1130 0.00 0.04 0.04 0.04 0.31 Samaniego Peak Samaniego Peak on Samaniego Ridge 1140 0.00 0.08 0.28 0.35 2.09 Dan Saddle Dan Saddle on Oracle Ridge 2150 0.00 0.00 0.04 0.08 0.71 White Tail Catalina Hwy 0.8 mi W of Palisade Ranger Station 2280 0.00 0.04 0.12 0.16 1.02 Green Mountain Green Mountain 2290 0.00 0.04 0.04 0.04 0.47 Marshall Gulch Sabino Creek 0.6 mi SSE of Marshall Gulch
BTW#2, true CMJs (cloud maven juniors) will want to photograph the rain from these shallow clouds, this rare, Hawaiian-like rain event2, lining the Catalinas this morning as soon as its light enough. It would be like photographing a parakeet on your bird feeder here in Catalina, one migrating from South America. I think that’s where they come from. Anyway, your cloud-centric friends from other part of the world would be quite interested in seeing your photos of this.
Is the summer rain season over?
No way! (But you already knew that, though it sounds more exciting to put it that way, in the form of a question like the TEEVEE people do)
Now we get into some interesting weather times as we go back into the scattered big thunderstorms feeding on the moist plume that accompanied O. That moist plume will be around for the next few days. These coming days, with their thunder squalls, may well be the most “productive” ones for rain here compared to the piddly output of O here in the Heights. We have upper air goings on that are likely to make storms cluster more into big systems a time or two during the next few days instead just the one over here and over there kind of days, the ones you hope you get lucky on to get truly shafted. So, “fun times at Catalina High” ahead, to paraphrase something.
The weather way ahead
Cool weather alert: based on model consistency, which I have already discredited earlier, there are cold snaps now appearing for the end of September and early October. They’ve shown up in a couple of runs now. They have some support in the NOAA spaghetti factory plots.
1There’s a nice description of “coalision” , the warm rain process not involving ice, in Pruppacher and Klett (1998) if you really want a nice book about cloud microphysics in your library.
2Mostof the rain that falls in Hawaii falls from relatively shallow clouds with tops at temperatures above freezing, no ice involved, contrary to the usual situation here where ice is necessary.
First, a tedious note about the Big One of two days ago.
While the Davis Vantage Pro 2 tipping bucket gauge registered a whopping 4.18 inches, a smaller plastic gauge from CoCoRahs here had 4.63 inches, after subtracting some rain (half an inch) I forgot to dump due to a brain cramp. A neighbor a couple hundred yards away here in Sutherland Heights, measured 4.65 inches in her gauge, and I now think that the 4.63 inches is the correct amount of rain for this spot. This goes with two other reports of 4.48 inches at Our Garden, and another one of 4.50 inches just a bit on the west side of Lago del Oro Parkway, and the 4.59 inches at the Samaniego Peak ALERT gauge just E of us. We seem to have been in the heaviest band of that storm! (Makes up for all the misses during the summer.)
The Vantage gauge is mounted above the ground, and some loss occurs due to wind, and also when the rain falls too hard, the tipping bucket can’t keep up. The CoCo gauge is ground mounted, and is protected from wind by surrounding natural desert vegetation (aka, “weeds”).
Below, from the University of Arizona’s rainlog.org, is a map of rain totals in our area and the northern areas of TUS. (The Our Garden and Samaniego Peak totals of 4.48 and 4.59 inches, respectively, don’t show up because they are not members of rainlog.org but probably should be so’s we can get all the rain we want to see in one site! I have added those values
In the meantime, from CDO at Wilds Road videos I took in heavy rain as the Sutherland Heights rain started to eclipse 3 inches, this larger wave that formed. I think it could have been surfed.
First of all, it was real disappointing to see so much haze in the air after so much rain! Not sure where it came from yet, will have to do some back trajectories to find out, but later…
The weather ahead
Still pretty confident in more summer rains and tropical air after the current dry spell of a few days, this partly associated with the next tropical storm, likely to be named “Opal” or something like that with an “O” as it takes shape. Of course, we could look up what name it will be, but it will be named soon enough, so why bother?Its already a numbered tropical depression (a weak area of low pressure) down there off Guatemala now.
Today will be a special one in the desert. Cumulus bases are going to be really LOW for summer, maybe only 3-4 kft above the ground, and likely warmer than 15 C (50 F). Maybe 50 F doesn’t sound special, but it is. A base temperature of summer clouds that warm is rarely observed here. And with that, and all the posts here about the temperatures that ice forms (around -10 C, 14 F) are out the window. Ice will form at much higher temperatures than usual.
This is because on a day when the Cumulus bases are that warm, rain forms by collisions between droplets before clouds even reach the -5 C (23 F) level, the highest temperature at which Ma Nature can produce ice. Rain mgiht even form in our clouds today even before the freezing level itself!
This is so exciting for an Arizonan who has studied ice-in-clouds development over the years because today ice will form in clouds around the -5 to -10 C level, and the mechanism of Mssrs Hallett and Mossop will be heavily involved as well as other lesser understood mechanisms to form ice in clouds today. And, along with that high ice-forming temperature will be categories of ice crystals that are rarely seen here, needles and hollow sheaths, ones that form at temperatures in clouds warmer than -10 C! You can see how excited Mr. Cloud Maven Person is. For comparison, it would be like a bird watcher seeing a _________, something pretty rare go by.
Dewpoint temperatures are running in the upper 60s and was 70 F (!) at TUS earlier this morning! Indicative of a really, really moist day from a cloud standpoint even now is that line of Stratus fractus cloud halfway down on Samaniego (Sam) Ridge. And this is BEFORE rain has fallen. Not too unusual to see something like that AFTER a good rain, but before, its pretty rare.
All in all, a very tropical day ahead, very “Floridian” I would call it, and that means more water in the clouds above us ready to fall out, and more “fuel” to send those warm plumes of Cumulus turrets spaceward. That’s because heat is released to the air around cloud droplets as then form, and the more “condensate” the more heat. The warmer the cloud bases, the more condensate that occurs. Its quite a feedback loop.
The last time we had bases this warm and low, some “lucky” areas got “Floridian” dumps of rain, that is, 3 inches in an hour. (Three inches in an hour is pretty common in Florida in the summer.)
However, need some heating and/or a good symoptic situation to gather up the clouds today if we are to get more than just high humidity from Norbert’s remains. Last night’s model run from the U of AZ was not real supportive of a great day because while the humidity is here, and upper level situation is going in the wrong direction, is not going to help much. A lot of what we needed was expended over night in huge storms that are raking central and northern AZ now, with some sites in PHX reporting up to 2 inches since midnight! And as that upper air configuration responsible for their great rains moves away, what’s right behind it up there, will try to squash clouds.
So, while we have the ingredients down low for an exceptional rain day, its not in the bag. What’s worse is that drier air is now foretold to roll in from the west by tomorrow, further diminishing (not eliminating, though) the chances for a decent rain here in Catalina. “Egad”, considering all the promise that “Norbert” once held for us!
So, in sum, a bit clueless here as to what exactly kind of day we’re going to have. “Truth-in-packaging” portion of blog. I see rain has formed just now (6:41 AM) on Samaniego Ridge, AND to the S-SW, very good sign!
—a note on air quality—as inferred from visibility in a humid situation——–
Another thing you will notice is how clean the air is. We have tremendous humidity, and unlike smog-filled air back east, the sky will be blue, and the visibility good. If you’ve ever been back East, you’ll know that in most areas the sky between the clouds on humid days is pretty white, and horizontal visibility is reduced in the moist air, say ahead of a cold-cool front in summer. This is due to large haze particles that have become droplets before water saturation has been reached, a phenomenon called deliquescence. Its horrible. Really ruins the sky back there on humid days.
Enough semi-technical blather. We’re mostly about pretty cloud pictures here.
There were some spectacular scenes yesterday, even though it was disappointing as a rain day, only a late afternoon trace here in Sutherland Heights. Here are some of the best.
6:58 PM. Ghostly-like late blooming Cumulonimbus calvus and Cumulus congestus clouds rise up against the falling temperatures. Pretty neat sight.[/caption]
Heck, if I worked on this much longer, the answer to what’s going to happen today would be in!
I wonder if you caught it? Fell between 8:10 and 8:12 AM. Very isolated, and pretty small drops. If you weren’t driving in it, or outside, you would never have known this happened. But observing and reporting events like this is what makes us who we are, you reader of CM. We take pride in seeing and observing what others don’t.
Before the rain hit, some two or three RW– (weather text version of “very light rainshowers”) began to fall to the SW of us from that deck of Stratocumulus clouds. Must have been where the tops were higher than anywhere else. Here’s the first sign, and upwind of Catalina, that you, as a CMJ (cloud maven junior) know to pull your car out of the garage. (BTW, thinking about having a CMJ cookie drive next month…so look around for your best recipes.)
It may seem strange, a non-sequitor, for those blog passersby to be talking about taking your car out of the garage or carport if a slight amount of rain might occur, as was the case yesterday. Here’s the “skinny”, as we used to say in the last century when we were young and could do things: a “clean” car, one that been wiped of all evidence of prior rain drops, but one having a thin coating of dust (you don’t have to apply a thing dust layer, its goes with the territory here) is great as a “trace detector.” And for us, CMs and CMJs, observing a trace such as yesterdays, when ordinary observers miss it (fumble the ball), is like hitting a low outside slider from former Husky pitcher Tim Lincecum, for a game winning touchdown. Or Boise State beating Oklahoma in a bowl game.
Why not just use the radar instead of parking your car outside and if the 24 h depiction of precip shows an echo over you, just mark yourself down as having a “trace”?
That would be cheating! Besides, some echoes seen on radar are only aloft.
And what if you’re in a “data silent” zone, where the radar beam is blocked by terrain, or is too far away? You’re adding unique information with your trace. Sure, nobody around you really cares if you had a trace or not, but, what the HECK.
Did the tops reach -10 C or so to form ice and cause this shower? Nope. Capped out at 0 to -5 C, so almost impossible to have had ice form to cause our sprinkles. Check this sounding from the WY Cowboys, who are off to a good season BTW.
In examining this TUS sounding closely, its good to remember that we are NOT Tucson, but in Catalina. We are 14 miles from the city limits; have a road sign that sez so. “Hey”, we aren’t even on the same side of the mountains as is “Tucson.” In fact, you have to go through the city limits of Oro Valley to get to Catalina! Only the Post Office thinks that Catalina is in “Tucson.” OK, got that in…
And, during the cooler season when troughs go by, as yesterday, the temperature profile from Tucson balloon is not accurate for us here in Catalina; its always that bit colder to the north and west of the balloon launch site for days like yesterday. So, like a chef, adding that bit more of butter or garlic, OUR sounding should be tweaked from the TUS one to show slightly higher and colder cloud tops, probably near – 5 C, not at ZERO or slightly cooler in overshooting Cumulus/Stratocumulus tops as would be expected from the Tucson sounding. Also, since it sprinkled at 8 AM, and not 5 AM, its also likely that clouds tops were going up some as the trough from the west approached yesterday. So there are lots of possibilities.
Sure wish we’d had a PIREP! (Texting form of, “Pilot report”). Any CMJ’s out there have an aircraft that we could take up and kind of poke around up there, see for sure what really happened instead of “hand waving”?
Absent aircraft reports, I am going to say that almost certainly yesterday’s sprinkle was a case of rain formed by “collisions with coalescence, or via the “warm rain” process (called that because it doesn’t have ice), sometimes called here, “coalision” rain. Very unusual in Arizona and, you can see that if you have to park your car outside to see how much came out of a cloud producing rain through “coalision”, it doesn’t amount to much.
You know, this is a great story for you. First, you observe rain that no one else did, or even cares about, until maybe you tell them it was almost certainly caused by collisions among cloud droplets, and then watch their eyes bug out!
Had some spectacular highlights again on the Catalinas, and also evidence of the aerosol loading as we say, in the crepuscular rays (colloq., crepsucular) shown below.
Since there is STILL no rain indicated for the next 15 days in the models, just dry (for now) trough passages, I may have to discuss yesterday’s sprinkle again tomorrow. Thinking of a title even now: “That sprinkle; more insights on what happened.” Yeah, that should do it.
Maybe they sneaked up because I wasn’t looking. After posting yesterday just after 5 AM, went out side and looked at the Catalina Mountains, that is those parts I could see through the thick rain shafts, and said, “WHAT!!!?” I was STUNNED to see them; had not even looked at the radar imagery for a couple of hours. Really was asleep at the keyboard.
And then the hour or so of rain that followed, with no lightning! Rain is so rare here om the morning in the summer, and it was so substantial. If there was a disappointment, a slight one, it was that Cargodera Canyon (NE corner of Cat State Park) with 0.87 inches, and the bridge at Golder Ranch Dr and Lago del Oro (0.71 inches) got so much more than we did here in Sutherland Heights in the past 24 h (0.38 inches). They were hit harder, too, by that late afternoon Cb that drifted off Pusch Ridge, again, a heavy shaft of rain with no lightning–how often have you seen that in a summer afternoon?
For a roundup of Pima County rainfall totals, go here.
It was, with its high concentrations of drops, a rain reminiscent of coastal Washington State in the early fall when offshore waters are still pretty warm, or Hawaii, for that matter, the latter location where most of the rain forms without ice. Our high concentrations of rain drops was also likely due to forming, at least partly, through the “warm rain” process, one that does not require ice, and is VERY rare in Arizona. Requires really warm cloud bases, and we had them yesterday, with bases around 60 F, 15-16 C, not too much cooler than you would find hovering over you in New Orleans or Miami, or Merida, Mexico, etc., places where warm rain develops routinely along with ice in the deeper clouds.
Here are some scenes from our huge, and low based, soft-looking, “soft serve” Cumulonimbus clouds, ones that looked that way because updrafts are weak for such deep clouds. You will see that updraft weakness in these photos.
This will seem strange, but I thought yesterday, with its absence of thunder until around dark to the NE, was one of the most unusual days I have experienced here in the summer, so reminiscent of the clouds in the Marshall Islands near the Equator that we (the U of Washington’s research aircraft) flew into during a ’99 field project down there; low, warm bases, high visibility under them, and clouds with weak updrafts and little lightning (the plane was only struck twice during the program):
Well, that’s about all we have time for, kids, and the hour of the exede.com choke hold, 5 AM approaches, and its too frustrating to be on the Web after that. May dredge up a Kwajalein shot at some later point, for comparison purposes, though.
Dewpoints are still running very high, even several 70s in the state (68 F here in the Heights). And so, with luck and no drying and no appreciable changes evident, we’ll have another day in the Phillipines, or the Marshall Islands, or Puerto Vallarta, New Orleans, Miami, Panama, etc. Enjoy.
About real clouds, weather, cloud seeding and science life stories