Virga here and there, chance of sprinkles through early afternoon, then blammo, clearing as wind shift aloft makes it way across Oro Valley/Catalina. CLouds will consist of Cumulus mediocris virgae, small Cumulonimbus capillatus virgae. Cloud bases will be below freezing and higher than Ms. Mt. Lemmon, so will be tough to get rain down to the lower elevations, though a virga trail may hit The Lemmon. Tops of Cu, -15 C to -25 C, i.e., cold enough for ice formation, of course. Crystals will be mostly stellars and dendrites with some clustering into aggregates we would normally call “snowflakes.” Some of the very coldest tops will contain some solid columns, maybe some prisms and hexagonal plates.
If you’re having trouble here because you’ve forgotten a few things, you might well want to get your Magono and Lee (1996) ice crystal “bible” and review crystals types and the temperatures they form at. Heck, maybe I’ll just put the first couple pages here for you…Magono and Lee (1966). Everybody had one back then. Very important to have that with you. As a further challenge, I have not rotated two pages to the upright position to make it too easy for you.
I suppose, too, that you COULD hire an small aircraft to go up there and check on these predicted types using the old “black glove” technique of the early 1960s, where a scientist would stick out a black-gloved hand from the passenger side of the aircraft and then report/log the ice crystals he found. Not making this up.
Yesterday’s clouds (something’s “wrong”)
Day started out dusty; ended up dusty.
Above, through the dust, for some perspective of our ghost “bear.” Pretty cool, huh? I hope there are some left by the time I get done with this blog! Maybe I should check….let’s see what the Canadians (well, one Canadian at U of Victoria) has to say about this dire sitiuation, get informed about stuff. Here’s a link provided by the climate provocateur, and former WA State Climatologist, Mark Albright, who forwarded it to me for my own illumination. I found that post interesting, unexpected…maybe you will, too.
Rain continues to show up on the forecast horizon, which is about 8 days
Best chance of rain, 21st-23rd, mods fuzzy on which day has the best chance. If you love spaghetti, you’ll love this one below. The vast change in the pattern, indicated for almost two weeks now, is just about here. Some mod runs have rain as this “trough bowl” develops, and a strong trough passes through from the west. Seems more likely than not from here that rain will fall as that happens.
The End. (Nice sunrise, lots of Ac cas, Sc, virga around!)
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:
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:
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.)
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:
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:
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?
Good grief, its already 88 F at 5 AM here in Catalina!
With a whole stretch of 100 F plus days ahead, maybe it would be good if we looked at some ice and thought about it. Below are some ice crystals, as photographed by Magono and Lee (1966), a publication that is thought of as the “bible” of ice crystal classifications. If you did or do field work on snow, in the air or as it fell to the ground, you likely classified the ice crystals that you saw as suggested by these venerable researchers.
Ice crystals have different shapes and different temperatures and saturation levels in clouds. Magono and Lee classified those shapes by temperatures and saturation levels at which they formed, and you can see some that in the pages shown here: Magono and Lee When you saw an crystal with a particular shape, or if it had frozen cloud drops on it, you then knew something about the temperature and humidity at which it formed; that crystal’s history so to speak.
“Factoid”: Nearly 100 percent of all rain that falls on us here in Catalina is that due to snowflakes, hail, soft hail (called “graupel”) that have melted on the way down. For example, those huge drops that first fall out of that big, dark cloud base right above you are without doubt melted hail or “graupel.”
As you examine at these natural ice crystals in detail, thoughts of cool air should come rushing over you. This is because the air in which these crystals formed would have to be cooler than about -4 F (24 F), the highest temperature at which a natural ice crystal can form, and even then, those only under special conditions.
I suggest meditating on each photo.
In general, the ice crystals shown below go from higher formation temperatures to lower ones. The first ice crystals shown, for example, are “needles.” They form at temperatures between -4 and -6 C. These are temperatures that moderate-sized Cumulus congestus tops sometimes reach, or winter Stratocumulus clouds. An example of using this knowledge in our module of “Converstional Meteorology” would go something like this. Lets say on a winter’s day, deep and dark in December (why does that phrase sound familiar?) that you saw some “needle” ice crystals falling on your dark jacket at the top of Mt. Sara Lemmon. The sky is cloudy in low Stratocumulus clouds, witih higher Cirrus clouds visible through the breaks in the overcast. I have made this a bit complicated to test your knowledge. It would be quite embarrassing for you and everyone who knows you if you then said, looking at those needle ice crystals (or even “sheath” ice crystals, “I think these fell from those higher Cirrus clouds we can see through the breaks in the overcast.” Instead, you would likely know that they must have originated within the lower, warmer shallow clouds and NOT from the Cirrus clouds overhead since the ice crystals in Cirrus clouds are mainly short stubby columns, and pointy ones called “bullets”, and sometimes in deep Cirrus clouds, bullet rosettes, ones that look like a “bouquet of bullets”, p55 in part 2 below. (Part 1 is ice former at higher temperatures, and part 2 are those ones that form at lower temperatures in general.)