A humilis day with a surprise ending; horse prank story

Yesterday was another great humilis day for you, with quite a phase twist at the end.  I am sure most of you out there saw the surprising final touch to a warm day with high-based shallow Cumulus.

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11:52 AM.
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11:52 AM. Cumulus humilis and fractus over the Catalinas, in case you think I was hiding bigger clouds that might have been over the mountains.
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5:15 PM. 95 and 25, temperature and dewpoint. What is the height of the cloud bases above ground level given a 70 degree F difference? Hint: divide difference by 5 and that’s the hieight above the ground in thousands of feet. So they were way up there at about 17,000 feet above ground level!

Let’s see how close that using that old estimator technique was yesterday by examining the Tucson sounding for 5 PM AST (launched around 3:30 PM, goes up about 1,000 feet a minute).  From the Wyoming Cowboys, this:

Ann 5 PM TUS sounding

Wow! LCLP was 515 millibars, just about exactly at 17,000 feet.  Also, look how darn cold bases were, almost -10 °C or 14 ° F, tops around -14 °C or just 7 °F, and yet we see no ice…yet.

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6:06 PM. Which way is the wind blowing at cloud level? Ans: at you. Nice cloud street streaming off the Catalinas over Catalina. Clouds not looking so much like Cumulus humilis anymore but rather more like Altocumulus opacus. No signs of any ice…yet.
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6:09 PM. Hint of ice in this photo of clouds far downwind of the Catalinas (looking north over Saddlebrook and beyond. Can you find it?
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6:52 PM. By this time, there was ice EVERYWHERE! It was an amazing transition from cloud lurking up there with no sign of ice, to ice in almost every cloud. Have hardly ever seen such a dramatic transformation in clouds that seem to be unable to produce ice most of the day. What happened? I don’t know. But will guess. These clouds, part of a moisture slug moving around the big trough coming in, were actually being lifted in time so that minute by minute they were getting a little colder until ice concentrations suddenly onset. Ice seems to depend on droplet sizes (the larger ones freeze at higher temperatures, AND temperature, the same size drop will freeze as the temperature falls. In clouds like this, the largest droplet sizes were likely the same before and after the transition to ice, so one would guess that the temperature at which they would freeze was reached as the tops rose due to a layer being lifted, not because some tops were higher and colder. The transition was too widespread and affected small clouds as well as the larger groupings. Well, lotta handwaving here, but it was an amazing change that transpired last evening.
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7:07 PM. Noticeable virga is now dropping out of those clouds, ice concentrations probably up to a few to tens per liter!
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7:07 PM. Looking toward the Charouleau Gap. Icy looking cloud over there, too. What is going on?
7:08 PM.
7:08 PM. Nice sunset, though. Ice barely visible at right.

While waiting for some rain in the days ahead, not backing off that in any way, though models generally have not had any (bad models!), will pass along a horse prank that happened.

Two days in the morning, as I went to fill “Zeus” water tank in the dawn hours, there was something dark at the  bottom of it.  I thought maybe some poor little animal or bird had drowned in his tank that night.  I reached down, and found it was my State Park baseball cap! I had left it on the top of a panel, maybe above the water tank, wasn’t sure, so it likely blew off the panel into the water tank.  But then again, I wasn’t sure that Zeus hadn’t put it in there on purpose.

But that was a crazy thought.

As a test, yesterday morning I decided to put the cap back on top of the end of a horse corral panel, but much farther away where it could not possible fall into the tank, just in case Zeus was telling me what he thought of me by dunking my cap.

9:41 AM May 4th.
9:41 AM May 4th.

Here’s what I found when I came back in the afternoon to feed Zeus:DSC_3630The same scene as the prior morning!

This was SO FUNNY!  But it was also endearing,

The End

The prankster, Zeus.
The prankster, Zeus.

Another Catalina rain day for May 2015

We received 0.08 inches here in “The Heights” for a third day with measurable rain in May already.  0.12 inches fell at the Bridge on Golder Ranch Dr. , while Saddlebrooke got up to a quarter of an inch (as estimated by CMP) in a tiny streak of clouds that erupted into shallow Cumulonimbus clouds, anvils and all yesterday afternoon between 4:30 and 5:30 PM. It was pretty much all over by 6:00 PM,  those shower clouds passing off toward Mammoth.

No rain was reported at mountain sites, to give you an idea of how localized that was, localized practically to Basha’s Market parking lot,  Sutherland Heights’ Equestrian Trail Road,  and Saddlebrooke’s Acacia Drive, to exaggerate some.

The astounding aspect of a tiny line of showers that suddenly erupted over and a little downwind of Catalina was that it was EXACTLY predicted  in the University of Arizona’s 5 AM AST model run yesterday morning, one whose results are available by mid-morning!  So, there would have been a few hours notice of possible rain here in Catalina.

There is no rain predicted in that model run anywhere else except in extreme NW Arizona, just that tiny ribbon of rain right over us, and the U of AZ “Beowulf Cluster” weather calculator got it right.

However, unless you were in the right spot, you might not have even known that it rained, the shower streak was so narrow.

Below, the astoundingly accurate predictions for 3, 4, and 5 PM for that model run from yesterday morning.  No rain whatsoever is shown at 3 PM, as you will see.
3pm

Ann 4pm

Ann 5pmTo be “fair”, NO RAIN was predicted anywhere NEAR Catalina by that same model crunching the data from 5 PM AST the evening before our little rain event, leading CMP to be a little asleep at the wheel yesterday morning, no blog.

Some cloud shots before and as this predicted (or unpredicted, as the case may be) rain began to happen.  Of course, if you want to go to the movies and see this, go here, from the U of AZ:  Yesterday’s cloud movie

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3:23 PM. Looking upwind. Nada going on, clouds to shallow for ice.
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4:04 PM. Hmmmm. Clouds definitely fattening up upwind of us in a nice cloud street from upwind of and over Pusch Ridge to Catalina. Nice scene, anyway, even if nothing happens.
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4:12 PM. Cumulus clouds are looking to gather down there at the corner of Pusch Ridge and Oracle Road, Huh. And they’re heading in this direction. Can ice really form in these guys today?
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4:23 PM. Clouds over and downwind of Pusch Ridge continuing to gather while heading toward Catalina. Looking for ice now or virga, but don’t see any anywhere.
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4:33 PM. Ice begins to show up in even modest clouds! And it started to show up everywhere in the form of virga. But then then the virga became thin shafts all the way to the ground. Cloud Maven Person is beside himself, but must go indoors for a social engagement!  Those of you who fancy yourselves as Cloud Maven Juniors, should have recorded this sighting of “first ice” in your cloud diaries for yesterday.
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Also at 4:33 PM. Ice is now readily visible in that Cumulus mediocris massing upwind of Catalina and is not about over the south part of the Catalina CDP (“Census Designated Place” that might one day be absorbed by Oro Valley, rumour has it.)
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4:41 PM. Just minutes before the first drops fall in Saddlebrooke, and CMP’s last photo of this incoming masterpiece of weather forecasting and little rain band; he can no longer comfortably jump up from dining room table in mid-conversation to say he has to pee again whilst actually taking a photo. You can only say you have to pee so many times in 10 minutes and still have your credibility intact. But, how can you say repeatedly, “I have to go look at some clouds?”, so I can’t hear the rest of your quite interesting story……”  Really came down for a couple of minutes several times there in Saddlebrooke between a quarter of five and 6 PM as one little raining cloud formed after another in this cloud stream.

Below,  sat view of this cloud streamer with radar, from IPS MeteoStar.  The image below is at the same time as the last photo above:

Satellite and radar imagery for 4:40 PM AST.
Satellite and radar imagery for 4:40 PM AST.  Note the many lines of clouds running almost due south to north into SE AZ from Mexico.

Here some more cloud stuff from the sounding launched at the U of AZ around 3:30 PM AST.

The TUS balloon sounding ("rawinsonde") for yesterday afternoon.  Looks like most tops were dabbling with the ice forming temperature of -10 C, but the sounding suggests that somewhat deeper tops could easily have arisen (and did!).  Interestingly, the model "knows" when ice forms, and it must have "known" that the ice-forming temperature was going to be surpassed in that little cloud line coming off Pusch Ridge.  Astounding, for the Nth time.
The TUS balloon sounding (“rawinsonde”) for yesterday afternoon. Looks like most tops were dabbling with the ice forming temperature of -10 C, but the sounding suggests that somewhat deeper tops could easily have arisen (and did!). Interestingly, the model “knows” when ice forms, and it must have “known” that the ice-forming temperature was going to be surpassed in that little cloud line coming off Pusch Ridge. Astounding, for the Nth time.  Bases were pretty cold, 0 C (32 F).

Here’s a diagram of when ice forms in the type of clouds we mostly have in Arizona, “continental” ones with high droplet concentrations, and when ice should form in them.  As you can see, ice should form in them soon after the top temperature gets colder than 10 C WHEN the base temperature is about what it was yesterday.

 

From a survey of the onset of ice formation in continental clouds by Rangno and Hobbs (1995)1
From a survey of the onset of ice formation in continental clouds by Rangno and Hobbs (1995)1

 

“CMP” is not mentioning it at all, but yesterday was another kind of mucked up sky, not a Catalina postcard sky,  with lots of aerosols making the sky a whitish-blue, the lower aerosol stuff again from Mexico, but there was also a layer far above the cloud tops, likely a long-range transport event from thousands of miles away.

This higher haze layer still seems to be around if you look toward the horizons right now (5:59 AM).

We’ll be between two jet streams today, kind of a jet stream sandwich, and the stronger one is now approaching from the northwest with that mega upper low over Cal.  That means no rain today, subsidence rules, though we’ll have small, non-ice producing Cumulus, and likely some Altocumulus lenticulars, maybe a Cirrocumulus patch here and there.  Should be a pretty nice day for cloud photos, haze aside.

The best chance for rain is still after midnight tonight into mid-day tomorrow as the core of the stronger jet stream goes just about over us.  Still thinking a tenth of an inch will occur here, though mod run from the U of AZ at 5 PM completely dry.   A little snow likely on Ms. Mt. Lemmon, too!

The End, FINALLY!  Brain empty.

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1From “A New Look at the Israeli Cloud Seeding Experiments.”

 

 

 

About ice-in-clouds and APIPs (or high temperature contrails)

6:55 AM
6:55 AM.  A surnrise glow from receding CIrrus spissatus highlights Samaniego Ridge.  Very pretty and dramatic.

 

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8:19 AM. Forming uncinus, CIrrus that is.  Note trails of precip beginnng to form under these tufts of Cirrus castellanus clouds.
9:06 AM.  Jet contrails begin to show up in a Cirrocumulus cloud.  You know what going to happen....
9:06 AM. Jet contrails begin to show up in a Cirrocumulus cloud composed of supercooled cloud droplets. You know what going to happen….something special for you to log in your cloud diary.

 

9:20 AM.  Another patch of supercooled, very supercooled Cirrocumulus with evidence of a jet contrail.  But, is the jet above or IN the Cirrocu?  TIme will tell.
9:20 AM. Another patch of supercooled, very supercooled for that matter,  Cirrocumulus with evidence of a jet contrail. But, is the jet above or IN the Cirrocu? TIme will tell.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

How cold were those Cc clouds?  See below.

(Begin technical module)

The Tucson balloon sounding for 5 AM AST, November 19th with writing on it.
The Tucson balloon sounding1 for 5 AM AST, November 19th with writing on it.  The height of these clouds was slightly lower in the mid-afternoon, but (as Altomumulus then) were still about -23 C.  As we know, cloud bottoms almost always get lower with passing time because the higher parts of cloud shields are moving faster.

In the mid- -20s C, around -15 F.  Height, about 21,000 feet above the ground here in Catalina.  Hope you got that estimate of cloud height right.

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Continuing…

9:21 AM.  ANOTHER jet streaks by!  This is going to be darn interesting, a rarity, like see a grey parrot in Catalina!
9:21 AM. ANOTHER jet streaks by! This is going to be darn interesting, a rarity, like seeing a grey parrot in Catalina!  The secret about what height the first jet was flying at is beginning to be revealed.  Can you see what’s happening to that first contrail a little below the new one?  This is a great test to see how far you’ve come as a CMJ (cloud maven junior)!

Here’s what happened in the Cirrocumulus cloud layer in yesterday’s special day, a pretty rare one, after the jets flew through it:

9:30 AM.  OK, mystery's over.  Even the average CMJ Joe can see that 1) the jets were IN the Cirrocumulus cloud, and more importantly, the aircraft contrails consist of ice.  Yes, that's right, the passage of the aircraft has caused a phase change from liquid drops to ice crystals, a lot of them.
9:30 AM. OK, mystery’s over. Even the average CMJ Joe can see that 1) the jets were IN the Cirrocumulus cloud, and more importantly, the aircraft contrails consist of ice. Yes, that’s right, the passage of the aircraft has caused a phase change from liquid drops to ice crystals, a lot of them.

 

9:47 AM.  Now those contrails are looking like real and icy Cirrus clouds.  In this case they're called "ice canals" but sometimes, when aircraft are ascending or descending and do this, they make round clear holes with ice in the middle, called "hole punch" clouds.
9:47 AM. Now those contrails are looking like real and icy Cirrus clouds. In this case they’re called “ice canals” but sometimes, when aircraft are ascending or descending and do this, they make round clear holes with ice in the middle, called “hole punch” clouds.

Lessons to be learned from yesterday’s supercooled clouds and the aircraft interactions inside them:

  • Cloud seeding works!  You CAN  make a supercooled, non-precipitating cloud produce a little precipitation that would not otherwise have occurred.

But in those situations where the clouds, say, are topping the Catalinas, they are often quite thin, and whether there is an economically worthwhile amount of precip is not known.  However, an experiment targeting those clouds would be the perfect “baseline” one in cloud seeding to establish how much we can wring out of non-precipitating clouds.   Things become kind of a mess when even randomized seeding takes on already precipitating clouds.

  • “Overseeding”,  as here in these clouds when aircraft produce prolific numbers of ice crystals in a small volume,  it leads to tiny ice crystals with low  fallspeeds.  Sure, they fall out and leave a hole, but they virtually never reach the ground except in one a in billion cases when the very cold clouds are real low, practically on the ground.
  • The Wegener-Bergeron-Findeisen mechanism produces precipitation.

Alfred Wegener, 1911, and  later Bergeron3 and Findeisen in the 1930s, came up with the hypothesis that adding ice to a supercooled cloud results in the growth of the ice crystal at the expense of the droplets.  They’ll tend to evaporate while ice is being added to the crystal via deposition of water vapor that was once liquid.  So, an awful lot, maybe most of the precipitation that falls on earth, involves “mixed phase” clouds.  This process has also been called the “cold rain process.”

However, let us not forget the two other processes that produce precipitation, the all ice process (no liquid required–helps produce “powder snow”, and the all liquid process, where cloud drops collide and grow into raindrops–the biggest measured drops in the world (about 1 cm in diameter) have formed soley through this process.  It is likely that most of the rain that falls in tropical locations like the Hawaiian Islands and in hurricanes is due to this process even when ice is present in the top part of storms.

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Later, we had some Altocumulus castellanus clouds with virga as the moist level lowered, though they were long gone before they could provide us with a nice sunset:

2:32 PM  Bands of Altocumulus castellanus approach from the west.  These clouds, while based at just about the same level as the Cirrocumulus clouds earlier in the day had three things going to produce so much ice, and really, convert to Cirrus clouds.  The cloud bases were slightly warmer, meaning more water was available to the cloud, the tops were higher and colder, likely around -30 C (-22 F), and perhaps as importantly, the drops near the top of the Ac turrets were larger than those in the earlier Cc clouds.  The larger the droplets, the higher the temperature that they freeze at.
2:32 PM Bands of Altocumulus castellanus approach Oro Valley from the west. These clouds, while based at just about the same level as the Cirrocumulus clouds earlier in the day had three things going for them to produce so much ice (right side of photo–and really, convert to Cirrus clouds).   The cloud bases were slightly warmer (the TUS sounding suggests, -22 C), meaning more water was available to the cloud, something that would impact the drop sizes in the turrets of the Altocumulus clouds (left side of photo); 2) the tops were higher than the Cc clouds (ones that were paper thin) and therefore,  slightly colder (probably about -28 C)  than those of the Cc clouds,  and perhaps as importantly, the drops near the top of the Ac turrets before they converted to ice, were larger than those in the earlier Cc clouds. The larger the droplets, the higher the temperature at which they freeze.  So, ice is more likely to form in a cloud with larger droplets in it than one with tiny droplets in it even though they are the same temperature.  That might explain the difference ice-forming behavior of yesterday’s very thin Cc clouds which mostly had no ice (until an aircraft came along in them) and these prolific ice-producing Altocumulus clouds, ones that converted to all ice.  Just educated guesses here.

 

Still looking for scattered very light showers in the vicinity tomorrow as a Mr. Troughy goes by.

The End.

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1Through the oral history tradition I learned while viewing the Washington Husky meltdown2 at AZ stadium on Saturday from a Mr. Mark Albright that the Tucson weather balloon launch site has been moved from Davis-Monthan Airbase to the University of Arizona campus next to their weather department.

2Late in the proceedings, with about 2 min left and the Huskies starting a play, and in the lead, CM was visibly  moved to jump up and say, “Don’t hand the ball off!”, as a gift to Arizona fumble occurred simultaneously.  But, being bifurcated in his loyalties now that CM is in Arizona and not with the University of Washington, he had to be somewhat “glad” that the Cats maintained their somewhat suspect but great win-loss record.

3From the Historic Moments in Weather collection:

Tor Bergeron and CM meet in Goleta.  His head was gigantic!  No wonder he was so smart.  CM, not so much.
Your Catalina CM and Tor Bergeron meet for the first time in Goleta, CA, in 1968 at the headquarters of North American Weather Consultants. Yours for $2,100 dollars, today only.   I remember thinking that his head was gigantic! No wonder he was so smart. CM, not so much.

Tropical fetches

Flash: Very light rain (R–) falling at 5:30 AM!  Amazing…  Won’t measure though, as thickest clouds are already sliding away.  But still, great to see, to smell the scent of rain in the desert, and feel the drops in this little surprise sprinkle!

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Forgetting about that last big bust, namely the last big trough of the season that let us down by producing no measurable rain, let us now consider tropical finches, or rather, FETCHES, since an example is coming soon, one that might well bring rain.  (I know what you’re thinking; you’ve heard that before, wrongly, I might add as in the LBT-LBB).   Hope springs eternal I guess, though rain is predicted by both the USA and Canadian models, so there is some mathematical backing to this hope.  See below, as rendered by IPS MeteoStar:

Green pixelation approaches Tucson-Catalina urban complex.
Green pixelation approaches Tucson-Catalina urban complex on Friday, May 29th at 5 PM,

 

Valid for 5 PM AST May 29th.
Valid for 5 PM AST May 29th.

Yesterday’s clouds

You can see them all at once from the great U of AZ Weather Department time lapse video for yesterday here in case still shots with captions aren’t enough action for you.

5:59 AM.  Virga falls from Altocumulus opacus.  This can also be seen as like a little slice of the tops of many rainy days when cloud tops aren't below about -30 C or so. As here, those tops are usually still comprised of mostly liquid droplet clouds in which ice crystals form, grow, and fallout.  If the air is not rising to replenish the doplet clouds, then you will be left with a patch of ice and virga, a patch that will eventually die.
5:59 AM. Virga falls from Altocumulus opacus. This can also be seen as like a little slice of the tops of many rainy days when cloud tops aren’t below about -30 C or so. As here, those tops are usually still comprised of mostly liquid droplet clouds in which ice crystals form, grow, and fallout. If the air is not rising to replenish the doplet clouds, then you will be left with a patch of ice and virga, a patch that will eventually die.  Estimated top temperatures, -12 to -15 C, a little colder than shown on the TUS sounding for yesterday near this time because we are farther into the cold air aloft than TUS is.  Also, it would be unlikely that clouds like these would produce ice at the indicated TUS balloon sounding top of Altocumulus at -11 C.   With their geerally small droplets, it needs to be colder than that.  Egad!   This is way too much info!  But what kind of ice crystals would you expect in a water-saturated enviroment at around -13 to -15 C?  Yes, that’s right, pretty Christmas tree stellar crystals, maybe some aggregates of dendrites.  Remember, too, for aggregattes to form that concentrations of the crystals must be more than about 1 per liter.  Too, since they are falling through a droplet cloud with droplets  larger than 10 microns in diameter, you would expect those stellar crystals and aggregates of dendrites to exhibit some riming, that is, have impacted some of the cloud drops as they grew and fell through the cloud, though keeping in mind that the crystals must attain a diameter of about 200-300 microns in diameter before riming commences, helped by the fact that stellar crystals (planar ones) fall face down like a clown does when he’s trying to make people laugh and trips over something.  Also, I think someone in that big house on the right is about to have a baby.
9:40 AM.  With all the cool air over us, it wasn't long before Cumulonimbus clouds began boiling upward, giving someone some rain.
9:40 AM. With all the cool air over us, it wasn’t long before Cumulonimbus clouds began boiling upward, giving someone some rain.
9:53 AM.  While Cu boiled up quickly on the Catalina Moutains, and iced-out a plenty, they never really got the depth required to produce much more than sprinkles and virga.  Can you spot the little bit of ice on the right side of this Cumulus mediocris?
9:53 AM. While Cu boiled up quickly on the Catalina Moutains, and iced-out a plenty, they never really got the depth required to produce much more than sprinkles and virga. Can you spot the little bit of ice on the right side of this Cumulus mediocris?
10:30 AM.  Nice example of the tremendous amount of ice being produced by such modest clouds (see right side here--nothin' but ice).
10:30 AM. Nice example of the tremendous amount of ice being produced by such modest clouds (see right side here–nothin’ but ice).
1:01 PM.  By early afternoon it was all over, the clouds too shallow, the tops too warm to produce ice even though they were still well below freezing.  Just the way it is.  Guess warmer than -10 C (14 F) at cloud top when you see a sky like this with no ice.
1:01 PM. By early afternoon it was all over, the clouds too shallow, the tops too warm to produce ice even though they were still well below freezing. Just the way it is. Guess warmer than -10 C (14 F) at cloud top when you see a sky like this with no ice.
6:47 PM.  Sunset so-so as high clouds to the NW blocked the sun so it didn't under light these clouds.  Here, Cu flatten as the heat of the day, such as it was at 85 F,  cold for late May, dies away,
6:47 PM. Sunset so-so as high clouds to the NW blocked the sun so it didn’t under light these clouds. Here, Cu flatten as the heat of the day, such as it was at 85 F, cold for late May, dies away,

The End.

Water, water everywhere in the sky, but not much fell on the ground

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.
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.
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.
6:54 AM. Altocumulus perlucidus undulatus, if you care.

 

 

 

 

 

 

Smoke attack

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.
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!
8:40 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 driving, 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 that might have been burning wood for heat, while aloft is another plume.  I could not tell where that came from, even in this time lapse from the U of AZ.  Note how the Stratus clouds in the morning change direction in movement.
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.

2:18 PM.  In the Catalina Mountains on the way to Deer Camp trail.  Cumulus humilis dot skies.  No ice evident.
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
2:18 PM. Cumulus humilis sitting around over Sutherland Heights, and the Oro Valley

3:21 PM.  In the Catalina foothills above Sutherland Wash.

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:2013022300_CON_GFS_500_HGT_WINDS_192

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.

The End.

Cold slam

That’s your weather forecast for today.  There’s nothing you can do about it.  Why go on about it?

Next, these from yesterday–was under control, only took 127 photos.  Every thousand or so shots I take is NOT of a cloud, and yesterday there were two exceptions, which I will post here as an anomaly; a quirk really:

5:48 PM.  Sun broke through the Cumulus and Stratocumulus clouds for this orangy foreground as the white light of the sun is burned orange at low sun angles by passing through a denser portion of the atmosphere.  The shorter wavelengths (blueish) are scattered out leaving reddish hues to come shining through.  Banner cloud remains in its same crevice on Samaniego Ridge like a trap door spider or a piece of lint in a corner of the room you haven't vacuumed for awhile.
5:48 PM. Sun broke through the Cumulus and Stratocumulus clouds for this orangy foreground as the white light of the sun is burnished orange at low sun angles due to having passed through a denser portion of the atmosphere and the shorter wavelengths (blueish) are scattered out leaving reddish hues to come shining through. Banner cloud remains in the same crevice as yesterday on Samaniego Ridge like a trap door spider or a piece of lint in a corner of the room you haven’t vacuumed for awhile.
2:55 PM.  Horse demonstrating that the appearance of water in a tributary to the Sutherland Wash was real, not an illusion.  Thanks, horse.  The bit of water in the Sutherland dried up just down from the private land fence opposite the rusty gate.
2:55 PM. Horse demonstrating that the appearance of water in a tributary to the Sutherland Wash yesterday was real, not an illusion. Thanks, horse. The bit of water in the Sutherland Wash itself dried up just down from the private land fence opposite the rusty gate on the east side. (Horse people know where this is.)
5:56 PM.  Gritty view through wires and a telephone pole of the highlight color of yesterday's sunset.  Sometimes I think you're here only for the eye candy.
5:56 PM. Gritty view through wires and a telephone pole of the highlight color in  Stratocumulus clouds of yesterday’s sunset. Sometimes I think you’re here only for the eye candy.

Yesterday’s rare ice-forming anomaly

I was hoping you wouldn’t read this far.  Something incredible happened, rarely seen here in Arizona. Our slightly supercooled clouds, with top temperatures between -5 and -10 C,  formed ice.  When I first saw the indication of something falling out of those shallow clouds on the Catalinas, I was beside myself.  Here’s what I saw, not taken while driving1:

11 AM.  A shopped photo of the ice fall on the Catalinas to make it look like it was taken from a car, the way you might have seen this.
11 AM. A shopped photo of the ice-fall from these Stratocumulus clouds on the Catalinas to make it look like it was taken from a car, the way you might have seen this ice fall.  Note how I cleverly tilted the image to make it look like it was taken in a hurry before the light changed.
Same image with writing on it.
Same image with writing and an arrow on it to help you out.

 

I thought it was some kind of fluke since it was indicated just yesterday from this keyboard, based on prior experience in Arizona, that ice rarely forms in our clouds at temperatures above -10 C (14 F).  Maybe someone was nefariously cloud seeding I wondered….  Or had flown an ice-producing aircraft through these clouds upwind somewhere.  (Its about what cloud seeding would do in marginally supercooled clouds like these, too, not much but something.)

———academic discussion—–

Ice appearance in clouds with tops warmer than -10 C is common in “clean” environments like over the oceans (see the works of Mossop in the Australian Pacific, Borovikov et al in the Atlantic, Hobbs and Rangno in the Washington State coastal waters and the Chukchi Sea offn Barrow, AK, or  Rangno and Hobbs in the Marshall Islands) in clouds with warm bases (ones substantially above freezing for the most part) that can be anywhere even in “continental” environments far inland where cloud droplet concentrations are high due to natural and man-produced aerosols (see Koenig in Missouri, Hallett et al in Florida, Rangno in Israel) among many others).  We sometimes have those warm-based clouds here in the summer, too.

——-end of academic interlude——–but not really——

These fuzzy very light snowshowers soon ended and the day went on as foretold, no ice in the clouds.While out on Old Jake, shown above, I was taking photos of particularly dark based clouds and was going to tell the story about why they looked so black, and yet did not precip–to warm and cloud top, and drop sizes near the top, too small for ice initiation.  Just about every case in which aircraft measurements have been made in such clouds that form ice at top temperatures above -10 C (14 F), inside them are cloud droplets larger than 30 microns AND a few drizzle drops (liquid drops between 100 and 500 microns in diameter, or rain drops.  Droplets larger than 30 microns and substantial concentrations lead to collisions where the drops that collide can coalesce into a single drop.  Let us not forget Hocking or, later, Jonas and Hocking and the 38-40 micron drop size limits they found for this to happen from lab experiments.  Below that 30-40 micron diameter size, the little cloud droplets act like marbles; too much surface tension.

OK, there’s that little discussion preparing you for what comes next.   Continuing with the story…was there one?  Well, anyway, Mr. Cloud Maven person, riding on his own forecast made that early morning for no ice in the clouds (meaning no rain), decides to also ride on his old horse, Jake, who needs some more of that exercise.

Confidently, though dark Cumulus clouds underlying a broken to overcast deck of Stratocumulus, looked even exceptionally dark in places, Mr. Cloud Maven person smiled at this darkness of the cloud bottoms, knowing that the darkness in the bases of shallow Cumulus only spoke to how high (and small) the cloud droplets were in those clouds; they had to be highly “continentalized”clouds, ones with tremendous droplet concentrations in them and because of that,  all of the droplets in them have to be tiny, being so great in number.  And, in being a Cumulus cloud with an appreciable updraft, even more droplets are activated in “continental” air than are at the bottom of a layer cloud like Altocumulus.

When the drops are tiny, more sunlight is reflected off the top of the cloud and the darker they get on the bottom, and the more removed they are from producing a drizzle drop, or are in having the precursor droplets to drizzle drop formation, cloud drops larger than 30 microns.

This is what a Cloud Maven person thinks before he gets on a horse….

So, as I am riding along near the Sutherland Wash, these patches of dark bases form nearly upwind….  I watch them for awhile, quite unconcerned, and smiled again, thinking about the other horseback riders, people on bikes out there that likely turned back in fear of a terrific downpour, not really having the knowledge they need about clouds.

Then suddenly I noticed ice streamers coming down NW of Catalina only a couple of miles away!  It was falling from the downwind part of these darker clouds, where after a period of time, ice, if it was going to form would be.  But, how could this happen?!!!!  Before long, the thicker regions of the cloud began to emit stranded precip, a sure sign of graupel up top in the cloud.  Graupel in clouds with supercooled droplets only 23-25 microns in size, much smaller than those required for coalescence, and the present of those droplets leads to ice splinters when they are banged by a graupel particle.  A coupla graupel (soft hail) and after awhile, (10-30 minutes) a cloud can have a lot of ice, 10 per liter or more in concentration, plenty enough for precip beside the graupel-melting to rain stranded part.  Here is a shot of the further, SHOCKING development:

3:06 PM.  First graupel strands emit from base of Cumulus congestus.  More ice aloft can be seen on the right.  Horse's ears show that he, too, is surprised by this sight.
3:06 PM. First graupel strands emit from base of Cumulus congestus. More ice aloft can be seen on the right. Horse, too, noting precipitation in the distance, is surprised by this sight.  “It’s OK, Jake, its over there and moving away from us.”
3:18 PM.  I smiled, a sardonic one, as the drops began to fall (see smudge, lower center).  A dark-looking complex of Cumulus topped by Stratocumulus had formed ice upwind of me, and now, me and horse were going to get wet.
3:18 PM. I smiled, a sardonic one, as the drops began to fall (see smudge, lower center). A dark-looking complex of Cumulus topped by Stratocumulus had formed ice upwind of us (see upper right), and now, me and horse were going to get wet.

I had to laugh at myself on the way back, the rain drops wetting us down, when I thought about being quite confident yesterday morning about no ice would form in our clouds.  When you have an occupation that tends toward error, its good to have a sense of humor.  There’s nothing worse than a humorless meteorologist at a party, one whose likely obsessing over his error-filled life.

So, why ice?  The TUS sounding at 5 PM AST did not suggest tops colder than -10 C Z(moisture top was about -5 C is all), but where the moisture ended, the air was incredibly dry, reported as “1 percent” relative humidity.  Here is that 5 PM TUS sounding:

Arrows point to main top height, and where the highest Cumulus tops might have gotten to as they momentarily, due to inertia, mounded above the main moisture level.  Normally, they plop back down because they get chilled, and the tops are cold relative to the surrounding air.
Arrows point to main top height, and where the highest Cumulus tops might have gotten to as they momentarily, due to inertia, mounded above the main moisture level. Normally, they plop back down because they get chilled, and the tops are cold relative to the surrounding air.

So, an overshooting top COULD have gotten to -10 C, and certainly, with that incredibly dry air just topside, those drops in those evaporating turrets would have chilled a couple of more degrees C.  So, maybe that’s it, in fact, the overshooting moderate Cumulus tops DID reach to, or below, the -10 C normal ice-forming temperature here.

However, the concentrations that developed in these clouds HAD to be due to other processes beyond just the run of the mill ice nuclei since there are so few of them at -10 C, and that where drops larger than 23 microns come into play.   Without those, there would never have been showers yesterday, only a very isolated drop or two.  Those larger than 23 micron size drops lead to “ice multiplication” where just a couple of initial ice particles can “multiply” like rabbits in clouds because of ice splinters shed when hit by graupel.  However, as we speak, the full understanding of how ice forms in clouds with these “high” temperatures has not been pinned down.  Some researchers, the present one included, believe that ice splintering alone is not sufficient to explain the rapidity in the appearance  the high concentrations (10s to 100s per liter) that develop in clouds like we had yesterday.  You probably don’t care about what I think, but rather go with the majority opinion…  Oh, well, it always safer that way.

As a test of even deeper knowledge that an aspiring cloud maven junior might have, this question:

What kind of ice crystals and other frozen particles would have been in those clouds yesterday?

Quiz music here  No help from the audience, that other person who reads this blog.

No cheating; don’t get out your Magono and Lee (1966) translated-from-a-Hokkaido-University monograph on ice crystals and the temperatures and humidities that control their shape.

Answer1:  What is a (hollow) sheath?

Answer2:  What is a needle?

Answer3:  What is a graupel (more a lump around a pristine ice crystal or frozen drop than just an ice crystal?

Answer4:  What is an amorphous ice fragment?

Congratulations and adulation!  You are now officially a cloud maven junior.  Don’t forget to order that CMJ Tee.

Below, examples from the “ice crystal bible”, Magono and Lee 1966:

Needles, followed by sheaths, followed by “lump” graupel, and then some ice fragments in the last two panels.

excerpted Magono and Lee 2

 

 

 

 

MAGONO AND LEE ORIGINAL PHOTOS 001 3
excerpted Magono and Lee 15
excerpted Magono and Lee 6
MAGONO AND LEE ORIGINAL PHOTOS 001 13
——————–

Only a crazy person would take photos while driving, like that crazy woman I once knew whose hobby was taking photos of dust devils while driving!  Oh, my.

Creepin’ Cirrus; pedantry on display

“Storms” at 30,000 feet, single ice crystals falling from various varieties and species of Cirrus clouds.  That’s about all we got for “weather” in the next few days as Cirrus creeps up from the tropics into Arizona.  But those Cirrus produce great sunrises and sunsets, so have camera ready.  And while not much is happening, you should practice logging what you see up there.

Cirrus clouds are the first clouds we see when something is up with the weather, even when it stays up high, but even in these “storms at 30,000 feet”, the moist level tends to decline over time, meaning there might be a chance for mid-level clouds to appear….such as, you guessed it,  say, Altocumulus clouds, clouds mainly comprised of droplets, in the near future.  That would be pretty exciting; mo’ better sunsets!

Maybe if it was a “cold one”, an Altocumulus cloud with virga hanging out of it, would give you a great opportunity to talk with your neighbors about the Wegner-Bergeron-Findeisen1 precipitation mechanism (be sure to use all three names to attain the greatest personal stature with them).

——–Warning!  Beginning pedantic unit———-

What’s “WBF”, you say?

Hell, you see it all the time!   Well, actually only once in awhile here in Arizona.  Below, in a pictogram,  is a representation of “WBF in action” from a few days into our cold spell just passed so you’ll know when you see ice virga hanging from a droplet cloud you’ll know what the HELL has happened up there. (Dry spells, such as we are in now, make me want to cuss that bit more.)

The background.

Your car has been parked outside all night, and the air was moist.  You finally wake up and go outside and you see that dew has formed on your car windows, well, all over.  But even though its a bit below freezing, not too much because we’re in Arizona, you also see that in a couple of spots,  ice has formed;  “horror frost” crystals as we call them here in Arizona because we don’t like frost and cold air of any sort.  (The real name is “hoar frost”, and watch out how you use that in a sentence.)  The remainder of the drops you see on the car are still in the liquid phase, or have JUST frozen.

But here’s the exciting, magical thing that happens around those “horror frost” ice crystals, demonstrated with a photo through a car window.  I’ve added stuff on this jpeg to help explain the magic show going on when the two, liquid and ice, mingle.

A recent example of the WBF in action.
A recent example of the WBF in action.

 

And what you see that has happened here is the same thing that happens in clouds when ice and droplets mingle, are co-located so-to-speak.  When an ice crystal forms in a droplet cloud, it becomes a vapor hog, water molecule hoarder, because at water saturation, the condition that results in the drops forming in the first place, its SUPERSATURATED with respect to an ice crystal!  Amazing, and CRITICAL for life as we know it on this planet because most of the precipitation that falls in mid-latitudes is related to this process.  We would have virtually no precip here in Catalina ever without this process.

What does that mean?  When the two phases are in proximity as here, the droplets nearest the crystal evaporate, and the ice crystal grows and falls out, usually, as precipitation.  Most rain on this planet is due to that process! There are two others that are also important, all ice, all liquid, but today I’m only talkin’ WBF, the “mixed phase” process.

In a cloud, especially a flat one like Altocumulus, this “mixed phase” condition results in ice crystals that grow too heavy to stay in it–its kind of like a “Thanksgiving-for-ice-crystals” inside a mixed phase cloud, and they fall out in those fine strands because they are so fat.

In another way, the ice crystals in a mixed phase cloud are like a low pressure centers, the droplets high pressure centers and the molecules move from high to low pressures.

Mixed phase clouds would go away completely, of course, UNLESS there was some upward motion to keep new droplets forming.  But, as in “Ghosts of the Perlucidus” blabbed about here a couple of days ago, sometimes there isn’t enough upward motion to keep the droplets “alive” and only a ghostly remains of the droplet cloud can be seen in a thin patch of ice.

Further detective work re the above jpeg.

Those ice crystals has to have formed when the drops around them were still liquid, probably just as the window reached a freezing temperature or a hair below.  If all the dew drops had frozen at once as clear ice, you would not have seen this crystal growth happen because everybody is in the solid phase, no “high or low pressures.”  So, while dew drops were forming and growing while the temperature dropped below freezing, there was something quite unique about a particle on the window that caused ice to form when most other places were quite happy to be liquid.  We call those special particles that might have triggered an ice crystal, “ice nuclei”, though, too,  there may have been a window surface imperfection that did it.

Anyway, ice nuclei are always much rarer in clouds than “cloud condensation nuclei”, particles that the cloud droplets form on.  A demonstration of that is in that photo above.

Cirrus clouds, almost never having water, “don’t need no water” because its often  supersatured with respect to ice above 30,000 feet without having a droplet cloud.  So, even without the water phase, an ice crystal can get fat and fall out in many Cirrus clouds, such as the revered, Cirrus uncinus with its pretty trails.  Veil clouds like Cirrostratus?  Not so much growth.

———-End of pedantic unit———

Yesterday’s clouds

You may have spotted those creepin’  Cirrus at sunset yesterday.  If not here they are, a classic example, ones that kind of drift up to the north out of the tropics into Arizona that from weak circulations down there, even in drought times here, periodically passing overhead, keeping our skies from being boring, particularly for those many of you who out there who are cloud-centric, head-on-a-swivel when outdoors:

5:48 PM.  Disant Cirrus, loaded with a few contrails, creeps toward Catalina.  Outta be here by now but its dark and I think I can make out something so this is not really a forecast because I kind of cheated by looking at the sky just now.
5:48 PM. Distant Cirrus, loaded with a few contrails because there’s an airway down there, creeps toward Catalina. Outta be here by now.   Its dark and I think I can make out something so this is not really a forecast because I kind of cheated by looking at the sky just now but I WOULD have said that without looking…  And if those clouds did get here, there might be nice sunrise for you.

 

What ahead?

Of course, there’s some rain on the model “horizon” (IPS MeteoStar rendering of WRF-Goofus model), but like that “puddle” on a desert highway on a hot day that you never get to, and I’ve tried, because it  moves away as you speed down the road, the “puddle” staying the same distance away, our model rains seem to do the same thing.   I’ve used this metaphor before, but I can’t think of a better one.   I think its pretty good, too; damn good, really, to cuss a bit more.  :} Here are a couple of examples of rain in southern Arizona from last night’s global model run to get your hopes up, most likely to be dashed:

Valid for 5 PM AST, January 28th, Monday.  Green areas denote the rain the model thinks has fallen in the prior 12 h.  Yeah, right!
Valid for 5 PM AST, January 28th, Monday. Green areas denote the rain the model thinks has fallen in the prior 12 h. Yeah, right.

 

Valid for 5 PM AST, February 1st, Friday.  I would gladly eat my words with whipped cream on them if this happens.
Valid for 5 PM AST, February 1st, Friday. I would gladly eat my words with whipped cream on them if this happens.

 

 

 
The END, FINALLY!
—————————-

1They’re not “mostly dead” now, but “all dead”, to crib a line from “The Princess Bride.”

Raining hard here at 4:08 AM

Little cell going by (aka, weak Cumulonimbus).  I hope you’re up to enjoy the sounds of a good cellular rain on the roof.  I feel like another song coming on.  Ooops, same one, but its a good one because it not only has rain and thunder in it, but also pathos1.  (I thought the thunder in this song gave it a lot of dramatic impact, and we had some thunder NE of Saddlebrooke yesterday afternoon around 2:45 PM.)

Cell has added 0.03 inches to our 0.13 inches and this morning’s total is now a quite nice 0.16 inches on top of the 0.30 we got yesterday.  Raining harder now after it let up!  Oh, that didn’t last long.  Dang.

Total here at 6:55 AM: 0.18 inches!  Two day total here, 0.48 inches.

This is so great since this second part of this two part storm was “marginal” as a rain producer, might have only produced 0.05 inches as the bottom estimate for rain, made a few months ago (just kidding), with a top possible amount of      0. 40 inches.  So, we’re getting close to the middle of the prediction range made so long ago, 0.225 inches, a prediction you may remember, one that was based on spaghetti.

This rain is associated with the strong cold front that passed through Catalinaland about 2 AM, just after those strong gusts occurred, 30-40 mph last night.   Here’s what the nighttime temperature did, drop 14 degrees!

And, as you no doubt know, the atmosphere pressure goes up instantly as the cold front goes by and the colder heavier air piles on top of you. (Time hacks don’t match on these charts for some reason–have not noticed that before….)

Arrow points to passage of cold front at Catalina, AZ.
Atmospheric pressure on top of you here in Catalina, AZ. Arrow denotes cold front and rise. With this denser air, you may notice that you’re having difficulty getting up, moving around as you push more “molecules” of air around for any given movement compared with yesterday when the air was not so dense. It also might be because you have more clothes on today…. Hahahaha

Here’s a really nice link to radar happenings locally from The Weather “Underground” (nothing to do, BTW,  with “The Weathermen” of the 1960s-70s even though it sounds like it).

Learning module….skip if bored already.

——————-

One of the things that is happening right now at 5:01 AM LST, is that cells are appearing on the radar or intensifying as they move toward Catalina.  This happens a lot when the air at cloud height is moving toward the Catalinas and upslope toward Oracle and Mammoth, getting squeezed between the Tortolita Mountains and the Catalinas.  That lifting  makes the tops go up to higher colder levels, and when the tops to the west and southwest are too warm for ice formation, say above -10 C (14 F), then just a bit of lifting triggers ice formation making a cloud “visible” on radar as the ice grows in size into snowflakes, maybe collides, too, with some itty bitty cloud droplets (too small to be seen by radar) growing even larger and falling faster.  This is maybe the biggest reason why Catalina has so much more rain than upwind areas (17 inches annual rain) compared with about 11-12 inches upwind.  Most of that difference comes in the wintertime in situations like this, and so some extent, like yesterday’s more general rains.

——————

What’s ahead for today?

Back edge of this rain band, more or less solid clouds dotted with deeper ones producing rain, is on the doorstep.

Here it is as of 4:45 AM from the U of AZ Weather Department Satellite Facility, with a CONSIDERABLE amount of arrows and writing on it:


So, according to this “diagram” the back edge of this band on the sat image should be here by no later than 10 AM today, that is, chance of additional rain up until around 10 AM in a brief shower, but only a hundredth or two likely.  After that, just clouds, probably a lofted Stratocumulus layer, then a widespread clearing with scattered to occasionally broken Cumulus.

Since it is so cold aloft now with the freezing level around 5,500 feet (snow shower now (7:29 AM) on Samaniego Ridge), ice will like form even in modest Cumulus clouds this afternoon, that means virga or maybe an ISOLATED light rain shower possible through around dusk.

Yesterday’s clouds

Here are some of the best cloud photos from yesterday, such a pretty day here in Catalina, where Cumulonimbus clouds stayed just to the north of us off and on all day.

1:19 PM. Cumulus congestus/Cumulonimbus with a young turret on the left that has not yet glaciated (though there is ice inside without doubt) and an older turret that one on the right that is completely ice.
2:31 PM. Cumulus mediocris/congestus over the Catalinas.
2:44 PM. This Cumulonimbus with a graupel shaft produced one roll of thunder.

 

 

 

 

 

 

 

 

 

5:24 PM, dessert. Some remaining Cu bottoms turn gold in setting sunlight. On the horizon, the frontal cloud band.

 

 

 

 

 

 

 

 

The End, at last!

———————–

1Actually, I made it sound like I wrote this song in yesterday’s blog, but in fact, I did not, though I WOULD have if I had thought of it.  Note that the person who uploaded this song to You Tube, did not know how to spell, “Cascades.”  No wonder we’re falling behind.

———————-

Gold above Golden Goose

Thought I would run down to Golden Goose Plaza here in Catalina to catch some sunset shots after I thought of this headline; “gold on gold” :{   Here are three shots from the GGP for your viewing pleasure:

5:48 PM. Altocumulus, no virga showing.
5:49 PM. A hot more to the southwest with Altocumulus opacus on the horizon showing snow virga.
5:50 PM. Zoomed shot to show remarkably heavy snow virga shaft (left of GGP sign) falling from that distant patch of Altocumulus.  Another shaft is visible above the white car.

Lesson time…  The clouds in the first shot aren’t producing virga.  Why?  Not cold enough you would guess, AND, the liquid cloud drops in them very tiny.  The smaller the drop, the more freezing is resisted in clouds, the larger the drops, and the lower the temperature, the more likely it is that ice will form.

When ice does form in a droplet cloud, the drops around the ice crystal evaporate and the vapor appears on the ice crystal, depositing on it as new molecules of ice.  Under a microscope on a glass slide, the crystal magically gets larger while a liquid drop next to it gets smaller and disappears.  This process occurs in clouds that are comprised of both liquid droplets and ice crystals and the crystals eventually fall out as precipitation.  The folks who described this “mixed phase” process, and at one time thought to be the only one that produced rain at the ground, was Alfred Wegner1, Tor Bergeron2, and Walter Findeisen.  We won’t mention “riming” an additive to that process today, which is the collection of instant freezing of drops by the falling ice crystals making them heavier…

This “mixed phase” (liquid and solid together) process is ALWAYS described in weather text books from elementary to graduate ones.  It requires the presence of droplet clouds and the introduction of ice to get the ball rolling.  Altocumulus clouds are always mostly comprised of droplets, and so virga coming out of them is ALWAYS due to the “mixed phase” precipitation process.  Tell your friends.

Here’s some surprising facts about yesterday’s Altocumulus clouds, even to me.

How high were those clouds?  Well, according to the TUS balloon sounding they were no less than about 27,000 feet above sea level, or about  24,000 feet above us here in Catalina, and along with that, they were extremely cold, with tops indicated to be about -30 C (-22 F).  The thinner ones on the right side of these photos would have been only slightly warmer, and as you can plainly see, had no virga, no ice in them even at those low temperatures!  Pretty remarkable.  In thin clouds like those not producing ice, you can bet the droplets were very, very small, likely smaller than 10 microns in diameter, and that small size of droplets is associated with a resistance to freezing.  Such clouds also tell you that there is a lack of what we call, “ice nuclei” up there, substances around which ice can form, usually soil particles.

In the clouds with virga off on the horizon (3rd photo), they are clearly deeper, meaning the drops were larger near the top of the clouds, AND likely a bit colder as well, both factors leading to prolific ice formation and heavy virga trails.  Hope this makes some sense.  Pretty skies, anyway.

The TUS sounding for last evening at 5 PM AST:


 

Today’s clouds and weather?

Some mid-level moisture is still around, and so more Altocumulus clouds, along with some Cirrus should move in during the day and evening hours with virga possible, since they’ll likely be cold again.  The U of A mod also sees lower, but very shallow Cumulus clouds likely, ones too warm to rain via the “mixed phase” process that you now know about.  So, rain chances are pretty dismal later today and tomorrow.  Nothing in the longer term, two week view either.   Man, this is a LONG dry stretch!

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1Remember Wegner? The meteorologist that came up with the idea of plate tectonics around the turn of the century? But the geographers/geologists laughed at him for about 50 years until they saw that he was right.  Why did they laugh at him?  He was a weatherman, not a paleogeographer/geologist ( i. e.,  not a member of the club).

2Here’s a photo of Tor Bergeron from 1968 in case you wanted to see what he looked like.  I don’t know who that is standing next to him…looks like someone who might have been influenced by Buddy Holly.