5:17 PM. Cu fractus and humilis with edge of the approaching rain band clouds starting to obscure the sun through a dust haze on the horizon.5:18 PM. Close up of setting sun amid dust. Yellow sun means larger aerosol particles likely due to dust. Tiny aerosol particles, due to smoke, lead to a reddish sun. Here there are likely dust and some smoke particles intermingled. A purely dust haze, absent smoke particles, produces a sun whose color is little altered at low elevations (see below).May 2012. Example of a sunset only impacted by dust, little or no smoke. Dust generally has particles larger than one micron in diameter, much larger than the wavelengths of light from the sun, and so those particles don’t interfere with it much; don’t scatter out the incoming shorter wavelengths as smoke would, and this lack of scattering keeps the sun looking pretty whitish. Pretty hard these days not to have some very fine smoke particles up there.
The storm: what about it?
Its here, such as it is. Stations upwind of Catalina and in the approaching rain band have been reporting about a quarter to one third of an inch this early morning in light to moderate rain. Seems that’s the most likely total here now, though our best model, from the U of AZ, has been indicating over half an inch in Catalina, and about a half an inch in Tucson. The rain may last only a few hours, but given our normal intensities, a quarter of an inch can pile up in a hurry (an hour) in these rain bands. Moderate rain is falling right now, 5:19 AM! Yay! Com’on rain!
Update: 0.15 inches in the first half hour here in Sutherland Heights Excellent.
BTW, this loop of rain areas every hour from the U of AZ shows that we here in Catalina will have the center of the upper level low pass directly over us! We’ll be in the spin. Pretty cool. You MIGHT even be able to see, in the distance, showers moving in different directions if you watch closely late in the day when it passes by.
The weather way ahead
The latest run of the wrf-gfs model, our best, and based on global data at 11 PM AST last night, has no precip here after today over the next 15 days, through January 4th.
Reason to be depressed?
Nope. This is where those crazy spaghetti (“Lorenz”) plots come in. They’re still indicating in their overall “messing around” that troughs here are a strong possibility near the end of December and early January. The ACTUAL model runs will vary from run to run tremendously in this regard, some showing nuttin’, then maybe the next one, having a big, cold trough near us. Stay tuned, “details at 11…”, aka, “later”.
Well, that cloud WAS “creeping” toward us after suddenly appearing on Pusch Ridge at dawn… Looky here:
7:14 AM. It thinks we’re not looking.7:25 AM. In only three minutes, a spurt toward Cartalina, hugging the mountains where its safe.7:44 AM. I wasn’t watching for awhile, and suddenly, there it was across from me!8:00 AM. By this time it was just sitting, pretending it was something innocuous, but I knew better.1:44 PM. By afternoon, it was gone… Or is it? You see, creepy Stratus fractus is afraid of the sun, twist and writhes in a death throe, evaporating right before your eyes when the sun comes out, or the weak light from the sun, as yesterday, warms the air up a little. Stratus fractus is truly cold blooded and only strong light will make it go away! The end. Below, some apropos music and commentary…
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With Halloween only 10 and half months away, I thought I would “get in the mood” and make up a little creepy-ness for the little kids who read this blog. Hi, kids! Hope you didn’t get too scared reading this. “Uncle Artie” is sorry if you did get scared.
What you saw in that sequence of Stratus fractus movement is also demonstrative of what often happens to smog layers funneling out of the Tucson area toward Mark Albright’s house in Continental Ranch, Marana. Here’s an example of creepy morning smog (smoke and other aerosol junk), partitioned to the lowest layers near the ground by a radiation inversion, a temperature reversal that develops at night that results in a temperature rise as you go up. In the afternoons, after the sun has done its work for awhile, the temperature DECLINES as you go up and the smog molecules are dispersed over greater and greater depths. Got it?
7:32 AM, December 2, 2013. Maybe you remember this morning. Smog stays down there until the sun comes up, and then slowly creepy-creeps toward Catalina and our foothills as the wind changes direction and comes toward us in the late morning and afternoon. Happens during stagnant weather patterns, not much going on. Fortunately, the heating by the sun disperses this goop into a greater depth so the smog seems less obtrusive, less visible, though its still there. BTW, the second arrow pretty much point’s to Mark’s winter home in Continental Ranch. Mark is a research meteorologist/climatologist at the University of Washington who got his feelings hurt when he corrected exaggerations of snowpack losses in the Cascade Mountains of the Pacific Northwest and people in his own department got mad at him for correcting those claims; happened back in 2005 or so. But, of course, it still goes on. Mark and his colleagues were proved right in the ensuing years of mountainous snows in the Cascades. Of course, a hundred years from now, well, that might be another story. Tune in later, maybe around 2050 to 2100. It is interesting that when me and Peter Hobbs was correcting cloud seeding claims found in the peer-reviewed literature, ones made by people in OTHER universities, the people in MY department loved me for doing so!
Now, where was I after that big caption….?
Oh, yeah, the weather on deck
Sunday marathoners, achtung!
Looking more like a dry day now on Marathon Day, Sunday, though a cold front will have gone by just before it starts. Looks like measurable precip will be partitioned to the north of Oracle on Sunday, but it will likely be cloudy with Stratocumulus clouds as the day starts, but those should gradually disperse into scattered to broken Cumulus clouds with virga by mid-day, some of those deeper Cu could produce a cold one; i. e., a sprinkle.
Jet core (at 500 mb, 18,000 feet or so) is well north of TUS as Sunday starts, and its really hard to get precip here until the core passes, which on Sunday will be later in the day. But then, the cold front has long gone, and the tendency for precip with the jet core has diminished (subsiding air behind the front is moving in then) to just scattered deeper Cumulus clouds having some ice-forming potential. Deeper clouds are stymied on the right side of the jet (looking downwind) overall in the Southwest in the wintertime by warmer air aloft and stable layers, the kind that produce lenticular clouds.
Below, what”m trying to say in words, is shown in this 500 mb forecast from IPS Meteostar with the wind velocities on it:
Winds at about 18,000 feet above sea level forecast for Sunday morning at 5 AM AST. No rain is also predicted by this latest WRF-GFS model run on Sunday in the TUS area.
Since this is an analysis from a model output, one inherently containing error, there is that inherent bit of uncertainty. So, you, as a weatherfolkperson, imagine what can go the best (the most rainful error), and the worst, and make outlier predictions. Potential rain here in Catalina on Sunday: max, a tenth (everything goes right); bottom, zero (or trace), in this case, as predicted by this model.
Way ahead
I will leave you with this. I think its looking more promising for storms later in the month. I think you’ll see what I mean:
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:
1:34 PM. Drizzling from Stratocumulus!
1:35 PM. Drizzling here. Hope you noticed and wrote it down. I remember how excited I was in 1986 when I was in Jerusalem and it drizzled! I did not expect to see drizzle there, and I remember how I screamed out, “DRIZZLE?” after putting my hand out the window of the modest hotel I was in. In those days, the cloud drops were reported to be too small by researchers there to form drizzle in them. Yes, Mr. Cloud Maven person was the first person in the world to report in a journal article3 that it DRIZZLED in Israel! One of the great things about blogging is that you can write ALL of the things that you like to read about yourself, and this one is no exception. I am really enjoying today, reliving past efforts and accomplishments since there don’t seem to be too many ahead….The late Jack Russell, flight engineer, listening to Art tell another cloud investigation story.
2:43 PM. Cumulus humilis field over Saddlebrooke.3:06 PM. Drizzle precip just a memory. These clouds too shallow to rain via collisions, and too warm to form ice.
Looking ahead….
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.
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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.)
We had a trace yesterday in SH. There was not ONE but TWO periods of rain, the first at 1236 to 1237, and the second from 1240 to 1240:30, both from the same cloud, but likely from different turrets protruding above the base. The drops were very small, barely mm-size, with considerably horizontal separation between them. Likely were from a few ice crystals that rimed up, became soft hail, then melted and evaporated on the way down to those tiny 1-mm sizes.
Here’s the key to recording trace events: First of all, you have to “want it”; have to have the fire in your belly like I do, that a day in which a small amount of rain falls is not getting by you as a zero rain day. In effect, you have to have a linebacker’s mentality. Be out there when it might happen, park your car outside overnight after cleaning the front and back windows before nightfall. Dust on it is especially good.
Now for yesterday and what happened, presented in detail so that you can improve your trace measuring skill set:
12:17 PM. Cumulus congestus lined up to pass over Sutherland Heights. Have to be ready. 12:29 PM. Its getting closer. Looks great for targeting. Was thinking with a little luck, a little more heating I’ll get shafted. No sign of ice at this point. None around either, so hopes are pretty exceptional.12:36 PM. Isolated drops falling, there’s one over there, and I thought I felt one, arms extended. But cloud is slipping slightly to east of me! No shaft coming out! But great looking cloud bottom. Will go into that collection.
:
12:40 PM. Another surge of little drops, can hear them on porch roof! Bottom not looking as generous as a couple of minutes ago.12:44 PM. Its over, cloud moving away now, feeling exhausted. Maybe I’ll have a cigarette. Not as much came out of the cloud as I had hoped for, No shaft ever developed; maybe a trace of ice visible overhead is all. But, nice view of the Catalina Mountains!
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Now, for that smog bank that moved in during the afternoon….THAT was a horrible sight, and kind of ruined the late afternoon sky views. The deep blue seen in the first shot was replaced by this whitish, hazy look, lots of “crepsucular” rays, in fact the whole sky got a bit “suckulent”, to misspell another word with purpose…. Take a look:
3:51 PM. Smog attack under way.
Likely will have the same stuff today. Origin? Well, seems to be coming out of the southwest and Mexico, but also may be old southern Cal smog. Here’s the GOES aerosol optical depth (AOD) image for later yesterday afternoon, 3:15 PM.
GOES AOD for 3:15 PM. Be glad you’re not in Bakersfield, CA! But note some smog over and to the SW of Tucson heading this way around low in central AZ. Colored regions denote smog; blue small amounts, orange and red, ugh, gimmee a handkerchief! Can’t measure AOD if too many clouds are present.
Today? Some smog, some pretty-but-dirty Cumulus clouds (ones with extra high droplet concentrations, likely darker bases than they really should have due to the “dirt” inside’em), and not much more. Maybe a Cumulonimbus off on the horizon somewhere.
Note: Images did not show up when posted yet are present in draft; first time for this happenstance in WP.
This just in, from last night’s global GEM model run by The Canadians. Using a magnifying glass, you can see that these panels show a tropical storm (now only known as Tropical Depression 12-E) moving into Arizona on the evening of September 9th (the panel with all the red coloring). Hmmm. Something to dream about, a final big greening rain; well, maybe just holding off the crispy period of our vegetation following the summer rains. In any event, the tropical river should be back over us, even if it misses, bringing some more of that summer rain.
The USA! “WRF-GFS” model have no such storm, so there’s no point in showing that model output, though it does get real showery here before and on the 9th. That would be good, too, though not AS GOOD.
Dreaming of what might come will help us get through the mini-drought and several day hot spell we’re now in I think. Today is supposed to be pretty much like yesterday, capped small Cumulus clouds, too small to form ice and precip.
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Yesterday you probably thought there were no Cumulonimbus clouds in sight. Maybe the haze and smoke were too much for you, and looking at local Cumulus clouds with not the slightest inclination to be more than “mediocris”, you gave up looking.
No Cumulonimbus sightings in your weather diary?
I feel sad that you didn’t see them, and you really didn’t need the telescope at the Stewart Observatory, but almost. The smoke and haze, which made the sky whitish, made it a challenge, maybe like seeing a spotted owl in Eugene, OR. Still, they were there. Here’s the physical evidence:
3:43 PM. Hiding through the haze, a Cumulonimbus calvus turrets. Still can’t see ’em?3:43 PM. Zoomed view of the same smogged up scene. See ’em now, just above and to the right of Twin Peaks?Same zoomed scene with helpful arrowing.
Where’s all the damn haze and smoke coming from after our stupendously clear days, ironically, during our high humidity and wet spell?
A 72 hour back trajectory of the air at 4,000 meters above sea level over Tuscon at 5 PM yesterday. Looks like it started out as a mid-level “long range” transport since this suggests that the haze was already up above 5000 meters three days ago.
Yesterday was a disappointment. Oodles of water up there above us, as represented by cloud bases somewhere around 15 Celsius (59 F) yesterday morning, early Cumulonimbus activity–one was up toward Oracle by 10:37 AM–Oracle got 1.06 inches yesterday, but while the skies darkened over Catalina several times, they didn’t “unload.” Maybe only once or twice before in six summers have I seen this darkening to the level we had yesterday, without a rain shaft soon falling out of it. A couple of examples from yesterday:
1:29 PM. A Cumulus congestus takes shape over Cat State Park, and heads toward Catalina. Only sprinkles fell.2:40 PM, looking toward Charoleau Gap. It doesn’t get more “portenful” than this. I was SURE a shaft would crash down, and with it, the WIND from the north, the clouds then building over ME to the south, as happens so often when heavy rains pour down on the Gap. Didn’t happen, at least not until too late, long after it had moved farther north. Got pretty dejected.
So, what went wrong? Why were the clouds SO DARK, even shallow ones like Stratocumulus, let alone the Cumulus congestus, but with so little “emitting power”?
The darkness of these clouds was surely due to the high smoky aerosol content of the air that led to unusually high droplet concentrations in these clouds. The higher the droplet concentrations, the darker the bottom of the cloud, say holding cloud depth constant. So, a moderately deep cloud, but one too shallow to rain, can look like these, like the normal darkness on the bottom from which blinding shafts of rain fall. So, most likely we were looking at smog-laden clouds, the kinds of ones in our future around the world because that’s what we do, produce smog and smoke, well, us and lightning.
And, as we recall from Squires and Twomey (1967), smoke inhibits the formation of rain in clouds. I am sure most of you remember that article about smoke and sugar cane fires in Australia, and how those smoked up clouds did not rain like the ones around them that were “clean.” This phenomenon has been reported on numerous occasions since, like how in LA it helps reduce drizzle (mist rain) occurrences.
However, as we know, even smoked up clouds can rain IF they get high enough to reach the -10 C level here because then copious amounts of ice, soft hail and snow will form aloft, and down it will come! That only happened in isolated places, like over Oracle where they got that inch of rain (at least around here). So another cause of dark clouds lacking in downspouts was that they were not QUITE deep enough for the tops to reach -10 C. up around 20,000 feet above the ground yesterday–those tops were SURELY so close, though!
Back to smoke effects. With bases as warm as 10-15 C yesterday, there should have been rain formed without ice, and almost certainly a little did (these eyeballs detected some yesterday afternoon on the Catalinas). However, this is the type of rain that smoke inhibits most. This is because with so many cloud droplets competing for a given amount of condensation, they all stay too small to collide and stick together (requires drops bigger than 30 micrometers in diameter (let us not forget Hocking and Jonas (1970)…. So, we lost some rain due to smoky skies there, too,
Next, it can be relatively cool with tremendous amounts of rain IF there is a good disturbance to cluster the clouds together, forcing converging air near the ground, taking it away at Cirrus levels. We didn’t have a “disturbance”, a trough or a low to help out.
Finally, without the help aloft, we needed, as you can all guess by now, that bit more heating at the ground, maybe just a few degrees was all to launch some really large but isolated storms.
Today?
U of AZ 11 PM mod run has Cbs developing over the Catalinas by noon, and during the afternoon some of those showers trail to the northwest over Catalina. I think one will. So, once again we have a day with rain around, and maybe today a little cell will bombard us with a quarter of an inch. Should be warmer, today and that will help since again we have no trough help. Still smoky, as you can see here at sunrise by that orange-brown layer below this morning’s Cirrus. So, once again, the clouds may look a bit darker than they “should” when we have clean air.
The End except for this nice morning shot of Ac perlucidus undulatus I would call it. Very nice!
6:54 AM. Altocumulus perlucidus undulatus, if you care.
Of course, the title refers to Dickens’ little known sequel (and frankly, a lightly regarded one) to his popular, “Great Expectations”. Dickens fully expected that by rushing out another novel similar to “Expectations” that a financial success similar to the one that “Expectations” had garnered for him would be easily acheived.
However, like most sequels, his effort was weak and appeared to be thrown together to merely take advantage of a gullible public. However, and much later, his sequel came to be regarded as a semi-clever, though lightly disguised, slam on the early English weather forecasting system, which was, of course in those days, was map-less, model-less, and mainly consisted of limericks and folk sayings:
“Birds flying low; beware the Low1.”
Forecasts were quite bad in those days in which Dickens lived, naturally, ships went down regularly due to unforecast storms, and Dickens wanted to dramatize this to his readers in his sequel; the various twists and turns in the plot of that sequel now thought represent ever changing, unreliable forecasts. He had hoped, with his satirical sequel, to provoke advances in weather forecasting, which he did. Isaac Newton, joined by Leibnitz, took wind of the Dickens sequel, and together they invented calculus, a tool which which allowed the calculation of the movement of air using the laws of fluid dynamics.
—-End of historical antedote2——————————
A surprising overnight rain
Well, even C-M and associated models like the Beowulf Cluster as of the 5 AM AST run on the 8th, did NOT see 0.38 inches from “Joe Cold Front”, who was supposed to pass by as a dry front, not a wet one. Still, it was fantastic surprise, one that could have only been made better by having forecasted it from this keyboard; going against the models big time. And THEN to hear Joe’s rains pounding on the roof as he went by between 10 PM and midnight. Oh, my, euphoria. BTW, the temperature dropped from 60 F to 43 F, too. Whatafront! Thank YOU, Joe.
You can see some rainfall totals from the Pima County ALERT gages (April 8th-9th rainfall). We “northenders” pretty much got the bulk of it, with Pig Spring, 1.1 miles northeast of Charoleau Gap leading the way with great 0.71 inches. Ms. Lemmon was not reporting at this time because it fell as snow. So look for a frosty Lemmon this morning. BTW, Sutherland Heights picked up 0.42 inches, and had “pre-rain” gusts to 58 mph! Whatastorm!
Continuing now at 7:21 AM after a “godaddy.com”/Wordpress meltdown an hour ago.
BTW, all the haze out there is dust under the clouds, not fog. Its pretty unusual to see something like this, especially after a good rain, so you’ll want to document it with photos and a little paragraph or two about it, and how it makes you feel. There was so much dust raised behind Joe throughout AZ and Cal that its rainband could only do away with that dust within it. This overcast situation should gradually breakup as the day goes on into more cumuliform clouds, ones with large breaks between them, the dust probably hanging on most of the day. With the -10 C level, the usual ice-forming level here at just around 11,000 feet above sea level. So it should be easy for the taller Cu to reach that and spit out some isolated precip later in the day.
Signs that the forecasts were going bad in a major way was when lines of clouds and some with precip formed in southwest Arizona late yesterday afternoon. Here’s a nice map of that development, one in which caused the tiny brain of C-M to think that it might rain, probably you, too, and anyone else that looked.
5:30 PM AST visible satellite image from the U of WA.5 PM AST 500 millibar map. You can just see that little line of clouds, and you can also see how the jet, wrapping around San Diego and headed this way, partitions the clouds. I think this is called a “teachable moment.”
Some scenes from yesterday’s dust, from the beginning. Save these for posterity:
8:21 AM. No sign of dust.1:47 PM. Dust haze becoming increasingly noticeable.2:00 PM sharp. Mr. Cloud Maven person’s cap blows off about 40 yards down the road in spite of having warned others about having this happen.2:04 PM. Dust increasing rapidly, wind peaking at 55-60 mph in the Sutherland Heights district. Twin Peaks no longer visible.3:02 PM. Small Cumulus (humilis and fractus) increase in coverage as dust limits visibility to around 10 miles.6:38 PM. The yellow sunset, indicative of large aerosol particles associated with dust.
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Feeling good about rain here, feeling good about rain there
Not only can we exult over a surprise rain of some substance, but look what has been happening in the droughty central Plains States. Below, from WSI Intellicast’s 24 h radar-derived rainfall amounts for the US (april 8th, then April 9th at 5 AM AST. Especially take stock of the amounts over the past two days in those worst drought areas of Kansas and Nebraska. So great! And this is only the beginning of a huge rain/snow event in those drought areas!
24 h rainfall ending at 5 AM AST April 8th.
The End
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1Hygroscopic insects adsorb water molecules and are weighed down in conditions of excess humidity, the kind that often precedes a storm. Birds then fly lower, too, to grab lower flying insects, or so the saying goes. (I am quite pleased by the kind of information I provide for you almost everyday.)
Let us compare different dusty sunsets, one from Saudi in 2007, and one from Israel, 1986, together at last for the first time:
Landing in a Lear, Qassim, Saudi Arabia, 2007.Dusty sunset on a beach at Tel Aviv, Israel, 1986. Dust (and warm weather) comes from winds from the south and southwest that have passed over the Sahara Desert, a fact known by local forecasters there for more than 2000 years. The clouds you will immediately recognize as Altocumulus floccus virgae. The slightly different colors may be due to using different cameras, the last from Agfachrome film. Also, aerosol composition may be slightly different, of course.
It was hard to see all the smoke around yesterday morning after the two previous stunning days with high visibility. I was thinking I had never seen so much smoke in Catalina as I saw yesterday morning. Here is some photos of that awful event:
7:56 AM. Heavy dark smoke layer evident to SW. Some Stratus clouds also were present.
8:40 AM. Normally, in my experience here, such smoke is husbanded to that region south of Pusch Ridge. But no, not yesterday, its HERE! What an awful view this was!8:45 AM. In this photo not taken while driving1, you can see that there are TWO plumes the lower one drifting south from the area of the Golder Ranch-Sutherland Wash development of expensive custom homes, some of which might have been burning wood for heat, or something else woody, while aloft is a second, separate plume. I could not tell where the higher one came from, even in this time lapse from the U of AZ. Note how in the movie the Stratus clouds in the morning change direction in movement. The movement at first is from the west-northwest (left to right), and those clouds contained the higher smog layer. So, could it have been from PHX??? ———– 1Smokey the Bear reminds drivers that only you can prevent smoky, well, a lot of it anyway.
In the afternoon, the smog was gone, mixed through a greater depth, the layering destroyed by the convection, those rising currents and compensating downward ones, that cream any morning layering. The dilution effect, and it also could have been that the aerosol load (smog) decreased with time, made things look much more clear. To this eye, there was still a lot of smog present, just diluted in the space between the ground and the bases of these small Cumulus clouds shown below. Still, there were so many pretty scenes on this horseback ride with a friend that I took more than 100 photos! Some water was present in some of the little washes, always nice to encounter, and some vividly green spots of of emerging growth (shown last).
The final point worth mentioning for pedantic reasons, is that yesterday afternoon’s TUS sounding indicated the same cloud top temperatures as the day before, about -12 to -13 C. Yet, there was no ice dropping out of those clouds. The day before, with the SAME cloud top temperature, ice and virga were widespread.
What’s up with that?
Ah, the complexities of ice formation in clouds!
When clouds are small and have a lot of droplets per liter in them, likely hundreds of thousands yesterday, given all the smog around, the drops end up being especially small because so many form on some of the smog particles (called “cloud condensation nuclei”).
In repeated flights at the University of Washington, we found that the resistance to form ice is dependent on not just on temperature, once thought to be the sole controller of ice formation, but droplet sizes in clouds as well. Small droplets sizes in clouds meant they were less likely to form ice, given the SAME cloud top temperature. Altocumulus lenticularis clouds are the poster child for ice formation resistance in clouds with their tiny drops, often having to be colder than -30 C before ice forms. On the other hand, clouds in the pristine Arctic around Barrow in the summer time, over the oceans away from continents, and in deep, warm based clouds even polluted ones, form ice at temperatures higher than -10 C when the drops in the clouds are large and have reached precipitation sizes (more than 100 microns in diameter to millimeter sizes).
So, it seems likely that yesterday, our shallower, pollutted clouds had smaller droplets in them than those deeper, less polluted clouds of the prior day in which we saw so much ice form in the later afternoon with about the same cloud top temperatures as yesterday. It is also the case, that when clouds are in large patches as they were the day before, that ice formation has more time to take place, and that, too, may be a factor.
Complicated enough? Yep.
2:52 PM. In the Catalina Mountains on the back from the Deer Camp trail. Cumulus humilis dot skies. No ice evident.
2:18 PM. Cumulus humilis sitting around over Sutherland Heights, and the Oro Valley
The weather ahead
After another round of cold, this one dry cold just ahead for us, the heat is on by early March, and along with that heat in most of the West in early March, likely record cold in portions of the East. Check this 500 mb map out for the afternoon of March 2nd, produced by last night’s WRF-GFS model run at 5 PM AST, rendered by IPS MeteoStar:
Look at the size of that cold trough and low center! Huge!
That isn’t the only weather news ahead, cold in the East, warm in the West in March. Our upcoming cold shock that hits on Sunday, is caused by an unusually powerful upper trough that dips down into Texas after it blows by us, then roars northeastward across the South on Monday and Tuesday. Expect to read about godawful tornadoes in the South on Monday and/or Tuesday.
Got pretty upset later yesterday afternoon when I saw these scenes off to the south through west, creating a little “sky rage”:
4 PM. View to the southwest toward Twin Peaks.4:58 PM. View toward the west and southern part of Tortolita Mountains.
Its not CIrrus or Cirrostratus you see, my friend, though as a nascent cloud expert, a CMJ, you may well have told a neighbor at the time of these photos, “Look, here comes the lead Cirrostratus undulatus (its had waves in it) clouds that precede our rain in a couple of days.”
You might even have gone on quite a bit about it, but you’d have been so WRONG and had to have apologized to your neighbor the next day, “after further review.”
What did you review?
The satellite infrared (IR) imagery, locally available. What would have been the obvious problem with your pseudo-astute cloud discussion?
If there is no cloud indicated in the IR imagery and KNOWING that if it IS Cirrostratus, no matter how thin, if its pretty widespread, as it is in these images, it WILL be detected in the satellite IR images1.
Let’s check if there is a cold cloud encroaching on Catalina around the time of these photos:
4:15 PM AST. Cold-topped clouds not even close to Catalina. What were you thinking, saying you saw some Cirrostratus? However, those high and cold-topped clouds ARE moving this way fast. Maybe we’ll see some lead Cirrus clouds on the horizon at sunset… Post event thought. See photo below.
Nope.
5:56 PM. Note thin linear shadows in front of Cirrus clouds.
Let’s also check, too, with our AOD (Aerosol Optical Depth) sensor on a satellite to see if it has any smog in it around here (below). Now this image below is an integrated view all the way to the ground, and so it can’t tell you what height smog is at. But, from the ground yesterday afternoon, we could “fill in that blank” by seeing that its way up there, probably at or above 20, 000 feet above sea level.
Below: valid at 3:15 PM. Shows region of thin smog clockwise, south through west through NW of Catalina toward where the first two photos were taken.
Next, after you’ve apologized to your neighbor, he might well ask of you, “Where did it come from, if that’s a smog layer up there?”
To prepare for such a query after you had learned that it was not a CLOUD, but rather smog, you would have used an estimate of its height (say, 7 km above sea level as a starter value), and gone to NOAA’s Air Resources Laboratory’s HYSPLIT model and prepared a few back trajectories for a few days, ones that end at Tucson, or even our exact lat and long. If you had done that, here’s what you would have seen this morning for a back trajectory for FOUR days, ending over Tucson at 5 PM AST yesterday for 6000 meters above sea level:
The star is the end point for 5 days of model calculated backward air trajectory for that air over Tucson at about 6500 meters above ground level, a first guess (not really) for the height of the smog layer in the photos. Other levels above this level look pretty much the same. Each fat triangle is a day. I put a LOT of writing on this, I HOPE it helps, but not sure. These graphs should have the start point for the vertical cross section at the bottom on the other side!
So, it would appear that our smog layer may have originated as part of something coming across the Pacific from Asia. There are no fires in Canada and in the Rockies that could have lofted a smoke layer like the one we saw yesterday. Confidence level? Moderate at best since the height of the layer had to be estimated by eyeball. You can go HERE to make your own plots like these, that is, to the Air Resources Laboratory of NOAA.
Clouds? Must talk about clouds.
There’s a lot of them headed our way. Check this annotated gif with writing on it from a couple of hours ago:
At 3:30 AM AST. I’ve written some things on it, and since we know from recent educational attainment studies that US students lack much geographical knowledge, like where the Pacific Ocean is, I thought I would see if anybody notices a problem here.
Big Pac IR loop from the U of WA Huskies Weather Department here. I had to use these images for the whole western Pacific down to the Equator so that you could see the whole of the cloud system that is now impinging on the West Coast of North America, from Manzanillo, MX, to Alaska. Pretty cool, huh?
Of course, as we know, the first of these clouds coming toward us, and for the next couple of days, will be high and middle clouds like Cirrus, a lot of Altostratus, and some Altocumulus. Might see, as happened yesterday afternoon, a Cu fra over the high terrain. (There is a little moist layer around 10,000 feet above sea level, according to this morning’s Tucson sounding.)
The rain gets here, the mods say, finally on Saturday morning, the 26th. There will be breaks in these high and middle clouds, and with luck, one or more super-spectacular sunsets/sunrises in the next three days.
Enough! Quitting…..TE.
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1Itty-bitty patches of Cirrus won’t be detected in the IR imagery. Its has to be a couple of square kilometers to be detected by the NOAA GOES satellites, the kind from which most weather imagery originates. Usually though, when Cirrus clouds occur, its detected because there are many larger patches besides the tiny ones. Tiny ones in isolation are rare, often associated with contrails.
