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A pretty day with some Altocumulus clouds and an icy mystery which isn’t really explained here

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Wonder if you saw it, this cloud mystery?  First the pretty and the plain:

2:53 PM. A nice example of Altocumulus perlucidus (flakes close together mostly). Hold the ice. How high up above you did you estimate this cloud is? I will estimate, before looking at the TUS sounding,
2:53 PM. A nice example of Altocumulus perlucidus (flakes close together mostly) transcudius (no gray shading to speak of),  hold the ice.   No ice was showing here in these clouds.  How high up above you did you estimate this cloud is? I will estimate, before looking at the TUS sounding.  I am going to guess 16,000 feet1, meaning about 19, 0001 feet above sea level.  If I am very close I will let you know, maybe spike a fubball.
Ann 2 2016091600Z_SKEWT_KTUS
The Tucson sounding, now launched from the Banner University of Arizona Wildcats around 3:30 PM AST, so its pretty close to the time of the Altocumulus layer. As you can it was at a height. (This being the political season, I am trying to obfuscate error, it was a little higher than I estimated, dammitall. Need more practice. Notice by having text below the arrow, it gives the impresseion of the cloud being lower than it really was. This is kind of a teaching moment in case you run for political office, or just like to play down your daily errorful ways. As meteorologists, we learn this early in our careers because there are so many, its overwhelming, really. (The Ac layer was at 25, 610 feet and at -22° C!!)  Cloud maven person, if that’s what he really is,  was off by a whopping 6,000 plus feet!  Egad!  And this height is higher than we really think of where Altocumulus layers inhabit, 22,000 feet above us yesterday.  Kind of embarrassing.  Humiliating, really2.  The only consolation I can think of is that other cloud estimators probably would have used a standard number, maybe “12,0001 scattered.”

Now for that icy mystery yesterday afternoon:

3:54 PM. An icy conundrumdrum-dee dum. Why there?
3:54 PM. An icy conundrumdrum-dee dum. Why there?

Let us zoom in some more, see if we can find out something:

3:52 PM. Zoomed view of one of the little anomalous snowstorms going on at 25, 600 feet yesterday.  If you click on this, you’ll see the tiny, delicate trails of ice falling out, ones that reflect a different set of circumstances for ice formation and growth that were present in that little cloud, seemingly so uniform, but not really if you were to fly through it with cloud instruments.

DSC_7910

However, we have really learned nothing about why SO MUCH ice fell out of a couple of those clouds.

CMP will offer a hypothesis, one that cannot be verified and so he can’t be shown to be in error again:

I think this may have been due to an aircraft passage in that layer, probably more than an hour ago.  Hypothesizing, it passed through some of the cloudlets and iced them up real good (that is caused ice to form due to its passage through it, not icing on the wings kind of thing, though that may be a part of the reason ice crystals form.   We’re not really sure what causes an aircraft to produce icy holes in clouds or ice canals.

However, in the longer term when an aircraft causes a hole or ice canal, if the layer is sliding upward, the hole  or canal fills back in with droplet clouds just like the one an aircraft glaciated.  Takes a lot of time for that to happen, at least an  hour since the upward slide in mid-level clouds is slight.

Another possible explanation to cover more bases, is that a very few of these now flat clouds once had turrets that stuck up to lower temperatures.  Only slightly cooler temperatures from -22 °C might have triggered what was clearly an explosion of ice.  But given the stable layer at the top of these clouds, that seems a less likely possibility to me.

3:55 PM. There was one more bit of ice falling out of one of these flakes. Look how tiny that strand is falling from a tiny flake! Remarkable. Since ice nuclei increase exponentially with lower temperatures, maybe a half a degree cooler Celsius at the tippy top of this flake compared with surrounding flakes triggered a few ice crystals.
3:55 PM. There was one more bit of ice falling out of one of these flakes. Look how tiny that strand is falling from a tiny flake! Remarkable. Since ice nuclei increase exponentially with lower temperatures, maybe a half a degree cooler Celsius at the tippy top of this flake compared with surrounding flakes triggered a few ice crystals.

Another thing we have learned today among the things we have not learned, is that clouds, especially mid-level ones, can be damn cold without having any ice falling out of them, and that ice falling out of them might even be an inexplicable anomaly!  Doesn’t really happen with clouds in the “boundary layer”, that is clouds formed from ground heating,  and/or connected to dirt and stuff through turbulence.  Too many chances for ice nuclei to get in them and most are  dirt particles like kaolinite.

The End.

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1When you’re speaking to friends, and to sound more pilot-like, more accurate in your cloud height assessments, its best if you say  heights as at, “one-six thousand, one-niner thousand,  two-five thousand”, etc.    As in, “I think those Altocumulus clouds are at one-eight thousand” as an example.

I really think if you talk like that to your friends when discussing cloud heights you’ll see a little bump of credibility for you.

2Its really OK to admit error, to be humbled once in awhile, get your feet back on the ground, not think of yourself as something special like you do.  In this regard, I have linked to an exemplary example of a media weather forecaster that was acknowledged a major error in a prior temperature forecast for SEA, but at the same time called out the correct elements of his/her forecast to blunt the fallout from the temperature error.   Perhaps, realizing, too,  that he/she/transginger, was using too fine a forecast “brush”,  learns from that and ends with a broader one:  An errorful forecast acknowledged:

2 thoughts on “A pretty day with some Altocumulus clouds and an icy mystery which isn’t really explained here”

  1. Hi Art: When it comes to “icy mysteries’ what do you think of “hydrometeors”- you know, those mysterious chunks of ice that fall out of the sky on occasion. Are they all caused by aircraft passing by- or is there anything else that might cause them. Just wondering about your thoughts on the subject.

    1. Hi, Roland,

      I’ll answer your query here first….

      In meteorology, rain, snow and hail are all considered “hydrometeors.” But I know what you’re talking about since the first U of Washington aircraft, a 1939 B-23, had “boots” to remove the ice buildup of the leading edge of the wing, and flexing those boots caused some pretty darn big pieces to come off! One slammed the observation dome (bubble) atop the fuselage, breaking through the plastic, and went inside it. My position in research flights was to have my head in the dome, and direct the aircraft into clouds. I had JUST sat down on preparation for landing when the piece hit and came through that dome. I was lucky. It was replaced by one with thicker plastic.

      art

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