Category Archives: Drizzle

Yesterday: a rare drizzle occurrence in the morning and later, gorgeous Cumulus-filled skies

First of all, Happy New Year to both readers! Thanks for hanging in there.

The weather ahead…

before a long diatribe about drizzle, followed by some pretty pictures with explanations:

Some picaresque Cirrus later today. Looks like next chance for rain is around the 10th-11th of Jan.

A rare drizzle occurrence

Cloud maven juniors were probably excited beyond description when they went out yesterday morning between 9 and 11 AM and intercepted a rare occurrences of brief drizzle here in Arizona falling from that low-hanging Stratocumulus overcast.  This happened after several very light RAIN (not drizzle) showers dropped another 0.02 inches, raising our storm total here in Catalina to a respectable 0.30 inches.

Drizzle is composed of drops barely large enough to cause a  disturbance in a puddle of water1, as though a large particle of dust had landed in it.  Drizzle drops nearly float in the air (should not be falling at more than about 3-4 feet a second), and in many cases of very light drizzle, the drops can float around like “desert broom” seeds. Visibility is usually lowered, things look fuzzy in the distance. Drizzle precip is so light it can’t produce even 0.01 inches except over periods of an hour or more.  Drizzle drops are also more uniform in size than the drops in rain, and are usually very close together.

While drizzle is common along the west coasts of continents in coastal Stratus and Stratocumulus clouds, its much rarer at inland locations such as here in Arizona, thus, the excitement over seeing it yesterday.

The reason why its rare in AZ?

Shallow clouds that drizzle must be what we would term, “clean” clouds; they don’t contain many cloud condensation nuclei and so droplet concentrations are low, maybe 50-200 per cubic centimeter (might not sound low, but for a cloud, it is). Clean evironments are found over the oceans and for awhile, in air coming inland along the west coasts of continents in onshore flow before it gets contaminated with natural and anthropogenic aerosols (smog).   Man, we are getting into a real learning module here!  Wonder if any readers are left?  Probably talkin’ to myself now.  Oh, well, plodding on. Nice photos below…far below.

Drizzle occurrences tell you a lot about the clouds overhead.  Not only are they low-based as is obvious (they have to be or the drizzle can’t reach the ground), but they are relatively shallow clouds no matter how dark they look.  Furthermore, and more subtle, they have larger cloud droplets (ones to small to fall out as precip) in them that must be larger than about 30 microns in diameter (smaller than half a typical human hair diameter).  When this larger size is reached in clouds, and those drops are pretty numerous, say 1000 per liter, they begin sticking together when they collide in the normal turbulence in clouds.  Those collisions with coalescence result in drops that fall much faster, bump into more drops, growing larger and larger until they fall out the bottom.

In a shallow cloud, those drops can’t get larger than drizzle drops, and that’s one of the ways you KNOW that they are shallow no matter how friggin’ dark they look.

Aside about rain not due to the ice process:
The largest drop ever measured, 1 cm in diameter, was observed in a Hawaiian Cumulus cloud that did not reach up to the freezing level!  Unfortunately, the authors of this finding did not publish their results and so did not get a Guinness record like me and Pete Hobbs did when we reported a smaller 0.86 centimeter diameter drop in Geo. Res. Lett., 2004–found them in Brazil, and again in the Marshall Islands–hit the pilot’s window like little water balloons.  Instead of being in a book with other famous people, like ones who can eat 47 hot dogs in 12 minutes, those researchers who encountered that larger drop in Hawaii sat on their finding! Unbelievable.

Strangely believe it, from lab experiments, drops bigger than 0.5 cm are not supposed to exist, but rather break up around 0.5 centimeters in diameter.  (hahahahaha, lab people). End of aside.

1Officially, 200-500 microns in diameter, equivalent to a couple or three of human hairs, maybe ONE or two horse’s tail hairs, to add a western flavor to the description.)

Yesterday’s gorgeous skies!:

Took more than 100 photos yesterday.  Was out of control, euphoric, thinking how great this earth is, maybe leaning toward thoughts of higher being and creativity therein, thus explaining the “creative” punctuation above.  Here are a few shots of those magnificent clouds and our magnificent, snow-covered Catalina Mountains.  First, those drizzle-producing clouds:

10:12 AM. Last of the drizzling Stratocumulus overcast. Patchy area of drizzle to west on the Tortolita Mountains here. The Stratocu gradually broke up after this time.


11:54 AM. Stratocumulus clouds still in charge, but lift here for a peak at the new snow on the Catalinas.
12:13 PM. First snow showers appear to the north-northwest as the stratocu deck begins evolving into Cumulus congestus and small Cumulonimbus clouds with large breaks.
12:35 PM. Snow showers from relatively shallow Cumulus race along the Catalina Mountains. These kinds of snow showers occurred right up until late afternoon.
12:37 PM. Snow and light rainshowers from shallow Cumulonimbus clouds also begin moving into Oro Valley before striking the Catalinas. Look at how similar these smaller clouds with their rain/snow shafts appear to our summer giants.
12:59 PM. Shower over the Oro Valley moves onto the Catalinas. Arrow points to a filament/strand coming out that is almost certainly composed of graupel (soft hail), something that was common yesterday from these clouds.
2:38 PM. HOWEVER, graupel often falls out of Cumulus congestus clouds on their way to being a Cumulonimbus without any sign of precip overhead, as here. This is because you are getting the result of the very first ice to form and fallout, usually those first ice particles are pretty rare in many of the shallow clouds as we had yesterday, and, because the updrafts are weak, they fall out as isolated little snowballs, too few to produce evidence of a shaft. But hang on, a shaft often, in the deeper clouds, imminent.
Also at 2:38 PM, looking northwest. A view of smaller Cumulus with the deep blue of the winter sky we love.
3:07 PM. “Congestus on the Catalinas.” You might ask, “where’s the ice?”, since yesterday all clouds reaching this size produced ice/snow/rain. Well, its on the other side (due to wind shear that carried the ice off toward the east. I think that’s the real reason why “the bear went over the mountain”, as we used to sing.

3:11 PM. Example of the medium Cumulus clouds (mediocris) that developed ice in them yesterday because it was so cold aloft, tops here colder than -12 C. (estimated).  Arrows point to ice, necessary for measurable precip here.
3:50 PM. Another modest Cumulus with plenty of ice (probably 10s per liter if you were guessing). Lowest top temperature likely lower than -15 C.

4:08 PM. I have no idea. This patch of ice cloud is left over, a “ghost” really, of a medium Cumulus cloud whose droplets evaporated. But what would it be called now? Altostratus translucidus cumulomediocristransmutatus? Cirrus spissatus cumulomediocristransmutatus? Silly, but I know of no name for such a patch of ice/virga
4:49 PM. You knew that on this cold day you would be treated to some of our finest scenes in winter, golden scenes of cloud-capped, snowy mountains, and later, those rosy under lit remaining small Cumulus and patches of Stratocumulus. What a fine day it was!

“Plenty more where that came from”

The models are showing a lot of rain ahead over the next two weeks–see farther down.  In the meantime, this:

6:44 AM:  back side of last rain blob passing over Catalina now.  That should be it for today and the next several days.

It was STILL raining when I got up at 3:40 AM, another few minutes of rain in a never-ending series of brief light rains over the past 24 h.  The total now over the past 72 h is no less than 1.34 inches here in Catalina!  Wow.

And yesterday, with its persistent overcast, dark, dull, spritzed-with-mist periods of rain (approaching the official “drizzle” precipitation category), was, with its high temperature of only 53 F, as close to am early spring day in Seattle in Catalina as you could experience.

Here are some shots of that overcast with Stratocumulus day with exceptionally long captions as well, a style I seem to have “pioneered”:

10:20 AM. “Catalina Heights” in the foreground, and the Catalina Mountains topped with snow and orographic Stratocumulus as seen from Shroeder Street, a street BADLY in need of re-paving but our priorities are so SKEWED, we think building three sound walls along Oracle in the near future is more important in this time of austerity!
Sorry, got worked up here over our 3rd World streets in Catalina, in which it is deemed a “fix” of a pothole by dumping a loose clump of asphalt in it. Still upset, too,  over the blockage of the CDO wash by sound wall on Oracle. Outrageous since there are no homes behind that section of the wall and beyond.
1:14 PM. Another area of light rain invades Oro Valley from the Tortolita Mountains to the west. This rain, having no strong shafting, tells you that the tops were humping up like rolling hills rather than are like towers. In humping up, they have gotten cold enough to have ice form in them whereas the other areas of Stratocumulus with no precip tells you they are too warm at top to form ice. SO Seattle-like here! TUS sounding yesterday afternoon indicated main tops at -10C (marginal for ice here) but likely humped tops to -12 C to -15 C, where ice can readily form.)
5:06 PM. Slight color under mainly non-preciping Stratocumulus. Oddity here is that orange, sunlit haze on the left of Twin Peaks. Seemed to be moving right to left almost like a dust episode.

















And this last rain episode, not even lasting 10 min, has plumped up the rain total for the past 24 h to 0.39 inches here in Catalina at 6:45 AM, ABOVE that amount that it was deemed there was only a ten percent chance of exceeding, 0.25 inches when writing yesterday.  So even as much of a precipophile as I am, I could NEVER have foreseen so much here as in the past 24 h!

So, this morning, I am humbled, but feeling great that so much more rain fell in our droughty nearby desert.

Two sites in the Catalinas have received another 0.87 inches as of 5 AM AST, 0.75 inches in the past 6 h!  View 24 h totals here, though being a rolling archive, unless you go right away you’ll see slightly different totals than I mention here.

This last 24 h of our rainy spell, too, is a good example of how Catalinans get more rain than in town WHEN the flow turns from almost due south as it was on Friday, to more from the southwest and west as has been the case yesterday and continuing into this morning.  When the flow is more westerly, air piles up against the Catalinas AND over us deepening the clouds, ones that begin thickening well upwind, say around I-10 to the west, and then they often start preciping soon after they thicken up as the tops of the clouds get colder and reach the ice-forming level.  When the flow is from due south, we are “shadowed” by Pusch Ridge and other portions of the Catalinas to the S, and our rain can be less than Tucson and the north metro area next to the Cat Mountains.

Most of our rain advantage over Tucson (17 inches vs. 12 inches) comes from the kind of days we had yesterday and early today.


What can we learn from these past 72 hours?

When you’re in a “trough bowl”, as we are now , good things happen; storms often turn out to be better than you imagine, being all they can be, no duds.

“Nice” days now will only be temporary breaks while we’re in the trough bowl, the collecting zone for storms.   As an exciting example of how the weather is in a trough bowl, there were TEN model output panels from last night’s run showing rain for SE AZ!  It can hardly be better than that!  Here are a couple of early panels with rain:

The 6 h ending at 11 AM today (unbelievable to me that its STILL raining in the mod then! Its like the “Miracle in Albuquerque” yesterday when the AZCats beat Neveda but had to score two TDs in the last 90 seconds to do it, doesn’t seem possible, will turn off TEEVEE and go do something else (as a friend really did. But there it is, its still raining here this morning, and a there WAS a miraculous win:
Valid for Wednesday morning at 5 AM AST. This is the rain accumulation in the prior 6 h indicated by the area of green.
Valid at 5 PM AST, Christmas Day. This follows a short break of several days, a break in which people get lulled into thinking its the end of the rainy spell, but they would be so WRONG! The rain shown here (green areas) is that rain the model believes has fallen in the prior 12 h (the period of rain lowers in resolution as the model gets farther away from its starting point; 6 h has become 12 h of rain areas.)













Go here to see them all, from IPS MeteoStar again.  Too many rain panels; too little space.  Quite the Big Bopper at the end of the run, too, on New Year’s Eve! One now wonders if after all the drought we’ve had, the sunny, comfy days, we’ll hear, after the next two to three weeks go by, complaints about how wet and cold its been?  Humans: we’re like that.  Me, too.  I like complaining, especially about sound walls.

In sum, we are in a “bowl game”, a “trough bowl” where storms will be collecting off and on for the foreseeable future.

Be ready!  It is the author’s experience that in some cases like this, the storms over a period of weeks, intensity, kind of go through a crescendo of sorts before the pattern changes back to dry again.  Hope so.   This would be great as an AZ drought buster.

The End.



Rain totals and some cloud shots and a bright rainbow

Pima County has a rolling archive of 24 h rainfall.  Below under “Table” are those totals as of yesterday, at 4 PM AST, probably that 24 h period capturing the full storm.  Here in Catalina, with another 0.21 inches after 5 AM, our 24 h total ended up at 0.96 inches; 0.98 inches at Sutherland Heights, 1 mi NE of this site.  The most in our immediate region is 1.57 inches at Pig Spring just NE of Charoleau Gap.   We seemed to have captured the most that this situation could have produced. ‘Bout time!

ALERT network Rain Table, 4 PM the 13th to 4 PM the 14th. Click “Table” to see.

After the steady rains of early yesterday the sky broke up into one reminiscent of a summer day with those cold Cumulonimbus clouds and dense rainshafts, and some spectacular rainbows. But some of our greatest beauty is when the sky breaks open and the clouds and shadows quilt the snow-capped Catalinas.

4:35 PM looking SE on the Catalinas and Pusch Ridge. An icy, pretty well glaciated Cumulonimbus cloud drops another inch or so of snow.
4:34 PM. Simultaneously, another cold Cumulonimbus cloud and its last bit of trailing rain produced this luminary. Typically brighter rainbows occur when the raindrops are larger. The bow ends at the top because its snow, not drops.  Its a nice graphic of where the snow level is.
2:28 PM. Stratocumulus top the Catalinas and water-covered rocks glisten in the the brief sunlight (look above road).
Also at 2:28 PM, farther north along the snow-capped Catalinas.  So pretty.


















1 PM. Example of the summer-like appearance of our cold Cumulonimbus clouds yesterday, this one over the city of Tucson.
3:08 PM. Another summer like scene showing a “Cb” moving into the Oro Valley.









What’s ahead?

Today:  Its raining now at 5:15 AM, what we would code as “RW–“, two minuses indicating “very light rainshower”, not measurable unless it continues for many minutes. (It didn’t.)  Some might have called it a sprinkle, but if you’re really weatherwise, you would NEVER call it “drizzle”!  C-MP (the writer) gets overly worked up when people call sprinkles, “drizzle.”

——small harangue—–

Drizzle, to repeat for the N+1 timeth, is composed of fine drops (less than 500 microns in diameter) that are close together and practically float in the air.  Umbrellas are much good in even the slightest wind; forget about it seeing well if you wear glasses and your riding a bike with a baseball cap.  A baseball cap can work pretty well in keeping your glasses free of drops in REGULAR rain composed of drops larger than 500 microns in diameter, mostly millimeter sizes, ones that fall rapidly, and don’t have time to get under your baseball cap unless its REALLY windy, or your going awfully fast.

—–end of small harangue—-

Now, where was I?

Oh, yeah…  We’ll have passing light showers today, maybe a few hundredths to a tenth of an inch is about all we’ll be able to manage today; if everything was perfect, a quarter of an inch. Better check the U of A model….see if it agrees.   Oops, not done yet, or is busted.  Oh, well.  We’ll continue to be north of the main 500 millibar current (see below), a necessary but not sufficient factor for rain here in the wintertime.  Means the clouds will be cold and ice likely to form in them as the day goes on and what sun we have deepens them up a bit, as well as an enhancement as our weak, incoming trough goes by during the day.  Anything is welcome!

Here’s the mid-day pattern aloft, from IPS MeteoStar:

Way out ahead

Its always exciting when you’re in a trough bowl, the location where the average position of one of the four or five waves (troughs) around the globe are.  When you are in one of them,  as we are, they function like storm magnets for your location.  Individual storms head in your direction, usually from the west or northwest, “bottom” out in latitude, then “eject” out to the northeast.  Our wettest SPELLS are characterized by the positioning of the average or “mean” trough in our location (“trough bowl” its been called here).  Doesn’t mean that it rains everyday, but there always a new storm heading in your direction until the pattern changes and the “mean” trough moves somewhere else.

So, we got another rain chance on Wednesday, looks similar to this one, probably light, but then later, the models are suggesting a chance for more substantial rains associated with some very strong troughs that move in within the 10-15 day range, or from December  24-30th.  Check out the size of this big boy on the morning of December 25th at 5 AM AST compared to what is passing over us today.  Note how much farther off Baja the main, broad band of the jet stream is flow.

Valid, 5 PM AST, Christmas Eve. Look at the clustering of red lines in northern Mexico in this cropped version. This jndicates that the forecast of an upper trough in this area at that time is VERY likely, not certain, but I’d out money on it.

I wouldn’t bother getting you excited about something this far out unless there was some good support in the spaghetti. Below is a cropped version of that plot (the full one below), concentrating on our area.

Remember what Edward N. Lorenz, an MIT meteorologist asked in the title of a paper when he developed the chaos theory:  “Predictability: Does the flap of a butterfly’s wings in Brazil set off a tornado in Texas?” (Thanks to the AZ Star for publishing this quote recently.)

So, in doing these “ensembles”, that is, running the computer models over and over again with slight errors deliberately introduced to produce these differing sets of lines in our “spaghetti plots, we are trying to see how different a forecast will turn out, with, figuratively, “butterfly wings” flapping around that we don’t know about.

If the lines don’t change at all from the original model run using the data that came in, then the forecast will be realized as it was first presented.  If the lines look like a bowl of rubber bands (as they are below in the full plot for Christmas Eve), then the forecast is unreliable, subject to huge changes in time.  But, those red lines south of Arizona are well clustered, indicating, figurotively speaking, that no “butterfly” is going to change it.  So, troughs predicted in the actual run for that time period, are almost certainly going to verify.

In sum, watch for a stormy period around Christmas.

Finally, the end, I think.

Dark clouds but no rain yesterday. What happened?

Quick answer:  1) drops too small to coalesce and form ones bigger ones ; 2) no ice in ’em, for the most part.

Read below if you want a LONG discussion about yesterday; dull photos way below

Let’s talk about it, though probably more than you want to.  You’re probably a little down because it didn’t rain yesterday, hour and hour though it looked like it should, except for a couple of “sprinkles-its-not-drizzle” drops.    You probably had to use your headlights in the middle of the day like people in Seattle do.    It began to clear up some, gradually, in the afternoon. Here are a few of scenes below, beginning with the morning overcast, with the last two shots between 4 and 5 PM AST as the clearing was underway.

So, what kind of clouds are they?  Well, Stratocumulus in the first shot, in the second shot a higher layer of Altocumulus or water-topped Altostratus1 is underlain by Stratocumulus and Cumulus clouds  (when the bases are more isolated, we call them “Cumulus”;  when they are more connected together, we hedge the name toward “Stratocumulus”.)

The third shot, showing Stratocumulus looks particularly ominous, probably the darkest part of the daytime was here around noon AST.  A shot toward the mountains next shows the underlying Stratocumulus and Cumlus below the higher layer of Altocumulus/Altostratus.  These clouds can’t be “nimbo” this or “nimbo” that because there is no rain to speak of falling from them.  (“Nimbus” means rain in Latin.)  Note the good visibility under all of the clouds; no precip there.

Finally, with the breakup of the overcast, shown in the last two shots, we can get an idea of the thickness of the lower clouds, at least at that point, about 2,000 to 3,000 feet at most.  Also in those last shots you will notice that the higher layer has moved away or dissipated, and with a bit more heating, the clouds are tending more toward Cumulus rather than Stratocumulus.

The higher layer, located at Altocumulus level, about 12,000 feet above ground level, was actually the cloud layer producing the sprinkles, and was a key player in how dark it was; two layers, naturally, stacked on top of each other, will make it darker looking than just one, especially, in this case, when they are both pretty shallow.   And with a top at about -18 C, you can almost be assured that the top was composed of mostly droplets, not ice crystals.   A droplet cloud reflects much more sunlight back into space than ice crystal clouds like Cirrus and Cirrostratus.

Anyone still reading?  I’m doing my best here…

That last photo demonstrates that in spite of having a little rain overnight, and even during the day, there was a lot of haze/smog in the air.  It wasn’t washed out by rain.  And, the more clouds get bunged up with aerosol particles on which drops can form on,   the higher the concentrations of cloud droplets are in them, and the smaller they are as a result.   Smaller drops cause more sunlight to be reflected back into space, and when that happens, the bases look darker.  In Seattle, in our airborne studies, it was usually the case to have darker based clouds downwind of the city, and light gray clouds near the coast and offshore, even when both cloud layers were about the same depth.  However, there are natural sources, like volcanoes that can also affect clouds this way.   For example, “VOG” (volcanic smog) in Hawaii darkens clouds there because VOG has particles that can form drops in clouds.  I seen it myself and I know a dark, polluted cloud when I see one!

What happens when you get smaller drops in clouds, as smog produces in them?  It makes it harder for something to fall out the bottom in two ways.

First, in smog filled shallow clouds, drops don’t get big enough to collide and stick together to form larger drops (something that happens when they get to 30-40 microns in diameter (about a third of a human hair in width).  But, even in the event that could have happened yesterday, drops got that large, the result would have been only TRUE DRIZZLE, fine, close-together drops that go under your umbrella if there is a breeze of any kind.  Very tough on people who bicycle and wear glasses.

The more important key to not raining clouds, was that the clouds did not have, IN GENERAL, cold enough tops to form ice crystals.  The lower ones seem to have topped out around -5 to -7 C (23-20 F),  temperatures at which smoggy clouds with itty bitty drops cannot produce ice.  

The higher layer, seen in the second and fourth shots, was just cold enough, about -18 or so at top from the morning TUS sounding, to form a few ice crystals.  Also, being higher, it was probably not impacted as much by smog.

Quitting here, brain exhausted.  Hope this is somewhat comprehensible.

The End

1The smoothness of that higher layer is due to ice crystals falling out the bottom, obscuring an Altocumulus-like cloud from which they are originating.  Sometimes this has been called the “upside down” storm because the top is liquid like Altocumulus clouds where it is COLDEST, but underneath is all the ice, where the temperatures are higher.  (Man, this is getting way too complicated to comprehend!)

So Seattle

Seattle nostalgia part

Got a little homesick yesterday with the weather the way it was here in Catalina.  Well, after 32 years in Seattle it seemed like home.  The dank, gray, low-hanging, lifeless, overcast skies of Stratus and Stratocumulus clouds hour after hour (spoken with emphasis on each descriptor using a whiney kind of emotional voice) reminded me of all the great times in Seattle, the friends, the occasional unsatisfactory girl friend (hahaha), the sports glory days in the Western International League semi-pro baseball league (well, there was one day in particular), the days as a Mariner batting practice pitcher in the equally dank Kingdome, an edifice that mimicked the skies outside, the 25 years or so of bike trips to and from the University of Washington under those same kinds of dank, gray, lifeless skies, and piddling rain we saw here yesterday.

And with people here driving around in the middle of the afternoon with their car lights on, it was the perfect replica of a Seattle winter day. Even the temperature cooperated here to mimic Seattle;  it only changed a couple of degrees from dawn to the mid-afternoon high of 47 F, some 20 degrees or so below normal.  Sometimes in Seattle, the temperature is the same all day because the sun is so weak and the layers of clouds, piled one upon the other, seemingly impenetrable to light and heat.

The Seattle mimicry was completed with some light rain in the morning here, raining just like it does in Seattle, barely accumulating hour after hour but there to annoy you.  We only had 0.02 inches after 7 AM LST, but it stayed wet all day here just like back at my old Seattle home.  The grass in the backyard there might be dry sometime in April, otherwise your shoes and your dogs come in wet everytime.

Yep, that’s what Seattle is like.   I loved it there….  Hmmmm.

Well, what I really loved was being at the University of Washington during the glory days of the Atmospheric Sciences Department when all the “big guns” in meteorology were there it seemed;  Holton, Hobbs, Wallace, Reed, Charlson, Fleagle, Bussinger, Leovy, Houze, and the job of flying around in clouds in the “CARG” aircraft, etc.  Their kind will not be seen, clustered together like that, anyway, again.  As a kid I tried to get autographs of the big stars in meteorology like Jacob Bjerknes at UCLA so that’s why being at the U of WA was so exciting.  They were to me like major league ball players were to other kids, though I did like Ted Williams and the Bosox in those halcyon days. Egad, enough!

A review of yesterday’s clouds below.  The first photo toward the Tortolita Mountains (obscured) and a near perfect example of Stratus, followed by two shots of Stratocumulus.

Weather and clouds part

Yesterday was interesting in several ways.  First the rain fell from clouds topping out at a modest -10 C, something we don’t see much of in Arizona.

Second, it was so dark during the day even as the clouds became shallower as the day wore on. Below are the two soundings from TUS for yesterday from the U of AZ, the first at 5 AM and the second 12 h later at 5 PM LST.  Where the green and white lines come together mark where the clouds were.  From that description you can see that they were topping out around 700 mb, or around 10,000 feet above sea level in the morning, and maybe 9,000 feet by evening at about -6 C.  No echoes were being observed by the afternoon.

But why?

Well, the cloud savant will know that there must have been a lack of ice crystals in those supercooled clouds in the afternoon (ones whose tops, at least, were below freezing.)  But why no ice?  Almost certainly it was because the cloud drops in those clouds were smallish, less than 25 microns in size, there were no “ice nuclei” active at those higher temperatures (a normal situation).  The lack of drizzle (fine misty rain that appears to float in the air) is evidence that the drops in those clouds did not reach sizes larger than 30 microns in diameter. Drizzle drops (those between about 100 and 500 microns in diameter, have often been associated with the onset of ice in clouds at temperatures of -4 to -10 C over the years.  But not always.

BTW, the formation of drizzle helps eradicate clouds by draining them of their liquid water, causing clearings.  So the absence of drizzle due to smaller drops helped “seal the deal” on a long day of overcast.  Also surprising to me was the amount of underlying haze yesterday, again evident in very strong crepuscular rays late in the afternoon.  See below, along with the rare example of liquid cloud mammatus formations.  That haze suggested to me that the drop concentrations in yesterday’s clouds were also pretty high, and helped keep the sizes of the droplets down by spreading the “condensate” on more particles. And guess what, those likely more numerous and smaller cloud drops helped make those clouds darker than clean clouds.   More sunlight is scattered back into space by dirty clouds than by clean clouds, so the bottoms of dirty clouds are darker even given the same thickness as clean clouds.  (This is a HUGE issue in global climate models, drizzling and not drizzling clouds because it effects the cloud cover, and the more cloud cover you have, the more CO2 warming is offset.)

So several factors likely went into making yesterday “so Seattle”; lack of precip later in the day, small cloud drop sizes, likely due to high droplet concentrations in those clouds, at least later in the day.  Lets hope it doesn’t happen again.   The End

Addendum on cloud seeding potential for yesterday

Yesterday was the perfect day for seeing what you can do by seeding clouds with dry ice–dry ice is more effective on days with marginally supercooled clouds.  Would there have been some rain on the ground?  You betcha with those low bases.  However, it is virtually certain that any rain would have been but a trace, or barely measurable.  The main thing that would have happened is that clearings would have ensued in the seeding zones, seeded by the way, by aircraft dropping dry ice into those tops.  So, a little precip, and some clearings, and those clearing would have likely triggered a widespread natural clearing if you could get enough holes produced by your aircraft.  The last photo shows would you can do when you glaciate a relatively thin layer cloud.   Were yesterday’s clouds thin enough for holes?  I think so.


Both the rainbow last evening, and in a momentary language lapse below….

A once-severe severe thunderstorm with warnings out at one time, whimpered into Catalina last evening giving us just sprinkles or, in aviation parlance, “RW–” (meaning, “very light rain shower”) And long with it, one of our memorable sunset views of the rocky faces of the Catalinas.  Total rain?  A “trace”; i.e.,  not measurable, but drops fell.

Once again I will take this opportunity in the event of very light rain consisting of sparse drops to educate:  Its not “drizzle”, DAMMITALL!

My apologies; probably shouldn’t cuss while educating.

What IS “drizzle” then?  The People of Earth, well those people represented by the United Nations World Meteorological Organization, have officially defined “drizzle” as “fine, close together drops that virtually FLOAT in the air.”   They are LESS THAN 500 microns (micrometers) in diameter (about five human hair widths) at their greatest size.   The smallest size is 200 microns, since drops much smaller than this do not fall fast enough to qualify as precipitation.  Note, some researchers have termed drops from as small as 50 microns to 100 microns, “drizzle” drops.

If any TEEVEE weather presenter uses “drizzle” in the context of RW– (sprinkles)  type of rain, please turn off the set immediately, change channels, send in some angry e-mails to this “pretender”.  Find a weather presenter approaching the status of a “real meteorologist” who knows his precipitation!  In this vein, let us recall the memorable words of the National Science Foundation sponsored program, “Bill Nye the Science Guy” and one of the little Disney Studios produced ditties, Water Cycle Jump:

“Your brain is on vacation, if you don’t know about precipitation.”

Feeling better now.

(This ditty,  my favorite one, of course, from that program….)  ((On second thought, I REALLY liked the “Smells Like Air Pressure”,  the Disney cover of Nirvana’s, “Smells Like Teen Spirit” too.  Very funny and yet educational!))

PS:  Remember in the olden days, when, say a baseball manager excoriated an umpire using “colorful” language?  Cussing was quite “colorful” back then.

First “storm” in the series, a trace of rain!

While taking the dogs out for their daily jaunt over the equestrian trails hereabouts yesterday morning, I was fortunate enough to experience several tiny drops of rain at 7:10 AM.  Rubbed a couple off the dusty car windows to be sure it was happening, it was THAT slight!   It lasted for maybe 15 minutes.  How tiny were the drops?  Oh, maybe 500 microns in diameter, practically “drizzle-sized.”  Recall this is ONLY THE BEGINNING of “stormy weather” in SE AZ, to quote a song title by Harold Arlen and Ted somebody.

What is “drizzle-sized” you ask?   Well maybe you didn’t ask,  but I am going to tell you anyway as part of a harangue about folks mis-indentifying drizzle occurrences.  It happens a LOT even with your local TEEVEE weather presenter (can’t refer to anyone who doesn’t know what drizzle is as a “meteorologist”!)

Drizzle drops are defined by official weather folk who know what they are talking about as those drops between 200 and 500 microns in diameter.  A typical human hair is 100 microns in diameter.  So, they are darn small and have so slow a fallspeed that they appear to float in the air. If you ride a bike, you will know that no baseball cap will keep drizzle drops off your glasses.   The World Meteorological Organization’s description, is “fine, close together drops.” Furthermore, unlike yesterday when those drops were incredibly sparse, drizzle occurrences are often noted by lots of tiny drops in the air, 1os per liter of air if you want a number, which I doubt.  This often causes the visibility to be reduced, but it is also close to saturation in most drizzle, sometimes the visibility is reduced further also by fog.

A common misconception today by those ignorant of what drizzle is, is to refer to a “sprinkle”  as “drizzle.”   A sprinkle is a smattering of much larger drops that fall rapidly; never appear to practically float in the air.  In the parlance of the old teletype weather reports, they used to be described in “hourly” station reports, such as at Tucson, as “RW–“, that is, “very light rainshower”, and NEVER as “drizzle”!  But for some reason, not sure why, there has been a corruption of the word “drizzle” to more often indicate “sprinkles.”  These have even crept into the official reporting records, particularly at military stations such as Davis-Monthan for some unknown reason.

Since repetition is important for learning things, I have copied the two paragraphs above and have pasted them below:

Drizzle drops are defined by official weather folk who know what they are talking about as those drops between 200 and 500 microns in diameter.  A typical human hair is 100 microns in diameter.  So, they are darn small and have so slow a fallspeed that they appear to float in the air. If you ride a bike, you will know that no baseball cap will keep drizzle drops off your glasses.   The World Meteorological Organization’s description, is “fine, close together drops.” Furthermore, unlike yesterday when those drops were incredibly sparse, drizzle occurrences are often noted by lots of tiny drops in the air, 1os per liter of air if you want a number, which I doubt.  This often causes the visibility to be reduced, but it is also close to saturation in most drizzle, sometimes the visibility is reduced further also by fog.

A common misconception today by those ignorant of what drizzle is, is to refer to a “sprinkle”  as “drizzle.”   A sprinkle is a smattering of much larger drops that fall rapidly; never appear to practically float in the air.  In the parlance of the old teletype weather reports, they used to be described in “hourly” station reports, such as at Tucson, as “RW–“, that is, “very light rainshower”, and NEVER as “drizzle”!  But for some reason, not sure why, there has been a corruption of the word “drizzle” to more often indicate “sprinkles.”  These have even crept into the official reporting records, particularly at military stations such as Davis-Monthan for some unknown reason.

Finally, I would like to insult you by quoting from the Bill Nye the Science Guy program, one sponsored by the National Science Foundation, BTW, and his science ditty, The Water Cycle Jump:   “Your brain is on vacation, if you don’t know about precipitation.”

So there.

Finally, here are the clouds that produced the drizzle as it was happening.  You are looking at the west side of the Cat Mountains and you can see that those “Stratocumulus” clouds are quite low based, necessary for drizzle drops to reach the ground.   However, I have to say that they were still a surprisingly great height above the ground for a drizzle drop to have reached me.  That drop HAD to be much larger coming out of the base to have fallen, say 3,000 feet and reach me as drizzle sized.  An alternative explanation that would go with the very sparse nature of the drops was that the clouds reached below the freezing level and a few ice crystals formed, which then grew into raindrops (bigger than 500 microns in diameter).  TUS sounding doesn’t support this, but, BUT, the bank of clouds over Catalina was NOT over TUS at the time of the sounding release, so I think this is still a viable explanation.

The end.