Category Archives: Definitions

What’s Up with This?

Got pretty mad yesterday when I saw this overhead in some Altocumulus perlucidus clouds.  You’ll have to hold your monitor or Ipad, or cell phone, or whatever, over your head to see it EXACTLY the way I saw this because it WAS overhead;  straight up.  (Actually, doing 3 sets of 12 might be good for you.)  Also, click on images to get the full view.

As you can see, the white strip below in these clouds is a contrail caused by an aircraft, but a special one that occurs in “supercooled” clouds.   Supercooled clouds are clouds that are composed of drops, yep, they’re still liquid, even though the temperature is FAR below freezing.  Here, the clouds were likely colder than -20 C (-4 F) and yet there is no ice forming in them!  (You don’t see trails of snow coming out, do you?  No.)  Run of the mill contrails occur at cirrus levels at temperatures below about -35 C  (-31 F).

Note that except for being much whiter than the surrounding cloud, the elements are exactly the same size and texture as those around it.  That is going to change, because this white strip is composed of “horrendous” concentrations (probably thousands per liter) of ice!   You can only know this by what happens later.

In the next shot below, is an example of what happens later, trails of tiny snow crystals fall out leaving a hole in the droplet cloud, so called, “hole punch” clouds, a form of inadvertent cloud seeding by aircraft.  Note the delicate strands of ice crystals falling out of this cloud from the hole, so pretty because they are so delicate looking.  Note, too, I am one of the “trailing authors” of the journal article above, like one of those itty bitty ice crystals in the second photo which are almost evaporated at the bottom of those fine strands.

So why be upset?

Rather than looking forward to good things in the coming year, this happenstance yesterday reminded me of all the trouble we had in the early 1980s trying to get our paper published on this phenomenon; namely, that an aircraft could produce tremendous amounts of ice when flying through supercooled clouds, inadvertently seeding them.

In the SECOND rejection of our manuscript (with Pete Hobbs), the Editors words still burn; “(the reviewers) are still unconvinced by these controversial claims.”

We had to do a LOT of extra work on this to convince those reviewers.  The third version was more convincing, I guess, for intransigent reviewers, and got published.  In fact, one of the great scientists of our time as far as clouds and ice crystals go, John Hallett (yes, the same one as in the “Hallett-Mossop” ice splintering process),  speaking at the Peter Hobbs Symposium Day in 2008 called this episode, “an embarrassment for the airborne research community.”  “Hey”, he wasn’t referring to our paper!

He was referring to the fact that such a phenemenon had been overlooked and not accounted for in research studies of clouds by aircraft.  Actually ground observers had been reporting this kind of thing (ice canals and hole punch clouds) since, if you can believe it, the 1930s!

BTW, this hole is not the one from the first shot; I got distracted and forgot to follow it until it was disappearing over the horizon.

BTW#2,, this shows what happens when you introduce ice into a supercooled cloud; “stuff” falls out.  Proves cloud seeding works, though for sure in limited venues like these (non-precipitating, supercooled clouds).

BTW#3:  The second photo is a nice example of the difference between supercooled clouds composed of tiny drops (probably less than 20 microns in diameter), and cirrus-ee ice clouds, composed of much larger crystals (here probably 100 or 300 or so microns in maximum size) that tend to settle with time. (Hence, those strands in most cirrus clouds.

BTW#4:  Today’s title is cribbed off the world’s most viewed climate website, “What’s Up With That?”  Mr. Watts, host of the site, has made significant contributions to our climate network by pointing out flaws, but has no “credentials” beyond having been a TEEVEE meteorologist.  He is excoriated on this point alone by “credentialists”, as I myself was when I first began to reanalyze other folks’ cloud seeding experiments such as this one.

BTW#5, a movie about credentialism is now out, called,  “The King’s Speech.”  I highly recommend it.   In this documentary, which I just saw yesterday, it will be seen that the credentialists in the King’s Court were royally put out by the help the King got by his uncredentialed therapist.

Arizona: Colorado temperatures, Colorado clouds

It was a mind-boggling, hiking-challenging -30 F at Grand Canyon AP yesterday morning.  Overhead of Flagstaff,  at 5 AM MST yesterday it was -38 C (-36 F) and that temperature was the lowest temperature at 500 millibars in all of the US.   It is really, really rare to see -38 C over Arizona!   Temperatures in the Tucson and north area in the shallow cloud deck we saw creep over the sky from the west near dawn, were running around -15 to -17 C (5 to 1 F) at cloud top (around 11,000 to 12,000 feet above sea level) according to the Tucson sounding at 5 AM.   Bases were just above Mt. Sara Lemmon.  For those of you who think I might lie about how high the bottoms of those clouds, I present a photo of Ms. Mt. Lemmon at that time (slight hump beyond first range).

Who cares, you’re thinking?  Well, in these photos, there is a curiosity; the lack of snow coming out of the bottom of these clouds (called “virga”, and you’ll want to concentrate when you pronounce this word so it doesn’t sound like a popular drug for older males).  Normally, in the Arthur’s experience,  clouds this cold produce virga, that is,  there are natural “ice forming” aerosol particles in them that  result in snow crystal that grows and falls out of the cloud, a lot of them so that the bases of the clouds are partly obscured by falling snow.

Also there was no radar echoes around at this time.  This was to change.

Here is a 30 h loop of the radar imagery for the whole US.  You’ll have to get a microscope out or zoom in a lot to see our area of SE AZ here, but, it’ll be worth it, he asserts.  Also, turn the loop speed up to the highest level at left on this web page, or you’ll get upset over how long things are taking to view. Don’t want any “Web rage” out there!  Too, I thought it would be fun for you to see all the echoes and the things they do over a long period, in a fast loop.   You’ll see here that around AM in our area of SE AZ there is a patch of echo that develops and then kind of hangs out over us until mid-afternoon or so when it disappears.

Here’s what the sky looks like when there is widespread ice forming in the clouds and falling out, MOSTLY as virga, and when we had that little patch of radar echo over us:

Note how “smeared” the sky looks now!  Also my apologies that a bird was going by obstructing some of the sky…

Well those heavier patches that are hanging down a bit and trail off to the side is what “virga” is.  Its often more spectacular than this, I have to say.

What happened to cause this rather sudden transformation of this layer, this sky; why did all this ice begin forming in that cloud layer when it had little or no ice over most of it around dawn?

I don’t know.  End of blog.

That would be a little too honest, and so I will guess. If you’ve worked in science, and this kind of thing is your specialty, its REALLY not good to say you don/t know something.

There was a disturbance aloft that was about to come through, and I will GUESS that the tops of this layer got a little bit higher and colder as it approached.  If you saw the clearing later in the afternoon, for example, your instincts would have told you about this event.  However, after it went through, and when tops were definitely falling in height, the Tucson sounding at 5 PM MST also indicated they were slightly warmer than they were on the first sounding in the morning, and so, I am, in effect, filling in a blank, hypostulating that there was a hump in the tops that was not observed.  Oh, well. If nothing else, you might now know the difference in the appearance of the sky when ice is not present (first two pics) and when it is falling out at you (last pic).

If you want to see an action shot of all the happenings described above, here’s a movie from the U of A Department of Atmospheric Sciences rooftop of the Catalina Mountains.  My location is under the leftmost portion of this view, beyond Pusch Ridge.  This movie will take a couple of minutes to load, and is only available today (for yesterday).

The Colorado connection:  Wintertime clouds in Colorado are generally as cold as our clouds yesterday, and are constantly producing falls of ice crystals and snow when present, and so to me, a six year resident of Durango, it was a “Colorado” wintertime sky over Arizona yesterday due to the really cold air over us.

Seattle comes to Catalina

Yes, if you’re from Seattle or the west side of the Cascade Mountains of the Pacific Northwest, you are going to feel especially at home today.   Its dark, even with the sun up, low ceilings and visibility, steady light rain mixed with snow, temperatures in the mid 30s to low 40s, well, that’s home in January.  And, here is that “home” right here in Catalina, AZ, for us to experience again!  Cloud type? Nimbostratus, often with an underlay of….Stratocumulus and Stratus fractus clouds to kind of provide that ragged, dark and gloomy, splotchy look.

As you may have experienced this morning, an extremely sharp cold front came through with a spectacular drop in temperature and a windshift at  6:30 A. M.   The temperature dropped from the upper 40s down into then upper 30s in only about 20 minutes, which it pretty unusual.  Along with the that temperature drop, the rains came in the “frontal band”, now totaling 0.80 inches here since the first period of rain began late yesterday afternoon (local weather station data here).  (BTW, this station’s wind data are averaged over 10 min, and gusts are 1 min averages.  Multiply gusts by about 1.5 to estimate the velocity of the strongest, few second duration puffs.)

This storm, still in progress,  brings the Catalina rainfall for December up to 1.93 inches.  Normal, based on a 31 year record provided by the folks at Our Garden here in Catalina, is 1.44 inches.  So with this storm, we have exceeded the normal AND crushed the monthly NOAA prediction of well below normal precip this month.  Yay!  Such predictions are partly derived from the effects of the strong La Nina now in progress-note colder than normal water along the Equator in the eastern and central Pacific.  La Ninas normally hedge the climate of the SW toward drought, and so this has been a great December if droughty conditions materialize later in the winter.  The December US-wide precip prediction, FYI:   (I should acknowledge a  bias here: I am overjoyed when droughty forecasts fail but also overjoyed when wet ones verify.)

Catalina-Smog before the storm

Those of us awaking this morning were literally a-palled by the amount of smoke around.  Not even Twin Peaks was visible, some 10 miles to the SW. See examples of smog in the photos below.

Where did it come from?  Back trajectories, ones that end in Tucson as of this morning at 5 AM shown below, suggest the smog came from the SE of us (red and blue lines.  The green line for air around 12,000 feet, represents where the air came from  that air came from the off the California coast ; it was too high to be involved in our smog episode.  Best guess, could be smog from El Paso and/or from burning in northern Mexico, that in the presence of light winds,  has kind of muddled around and drifted N into Tucson.

Note the pooling of smoke in the low valley ahead in the Golder Ranch area in the first photo.  Probably the result of wood-burning stoves used in the small housing development back there.  What it shows you is the persistent nighttime inversion that forms in that bowl, the flat top of the smoke indicating a temperature inversion. You then see a “clear slot” of little smog and then the overall deeper smog layer above that, also very laminar in appearance.   With the sun’s rise over the mountain, that kind of structure/separation is soon removed as bubbles of warmer surface air float upward and are replaced by downward moving blobs, mixing all the structure you see in the first photo out.   In the last photo, a few tiny cumulus fractus clouds composed of droplets have formed over the Catalina Mountains.  The droplets in those clouds are probably 10 microns in diameter (about 1/10 the size of a human hair).   These droplets are about 100-1000 times bigger than the aerosol particles making up the smog.   This makes the clouds to tell from transparent haze blobs because the smog particles are too small to scatter much light while the cloud particles even in small clouds, prevent you from seeing through them.  Well something like that.

Hang on to your hat tomorrow; windy, thinking momentary gusts here in “Catalina Heights” will hit 30-50 mph by late afternoon and overnight before a very strong cold front rolls through around dawn tomorrow.  This is an unusually strong upper level AND lower level system with a deep low expected to form over southern Nevada during the day tomorrow.   Looks like the rain could change to snow above  3,000 feet after the front goes through, too.  That would be terrific!  The clearing after the front goes by will probably be late in the day with passing light showers possible until early Friday morning.  The ones later in the day and overnight, are likely to be snow flurries above 3,000 feet .  Don’t expect the temperature to do much tomorrow. And, the amounts of precip are likely to be substantial putting us at or above normal for the month.  Yay!   Well, this what it looks like to me; check the NWS for the official forecast!


Many of us here in SE Arizona will not be outside today no matter how nice it is because of historic sports emergencies that will require viewing of the TEEVEE at all times.  However, if we do go outside to BBQ some hot dogs or prepare other similar worthwhile foods common to “football day”, there will be LOTs of icy cirrus clouds to view,  such as those in the photos.

However, there is also likely to be the quite odious contamination of these clouds by aircraft contrails as we have seen over the past few days. Aircraft produce long contrails when the air is at or near “ice saturation” and the temperatures at flight level are below about -35 C. Flight levels over Arizona for aircraft traversing the state are typically between 32,000 and 38,000 feet and the temperatures at those levels are almost always low enough for contrails.   Its only the moisture that is usually missing to allow them to happen.  These flight levels may be tuned depending on headwinds.

Often over Catalina, AZ, we only see contrails to the N for the heavily traveled airways above Casa Grande to PHX or to the S of TUS.  Lately there seem to have been an abnormal of contrails.   Not sure why.  The TUS balloon soundings have suggested that it is damp up there from about 25,000 feet to more than 40,000 feet over the past couple of days, the highest levels of that moisture a bit high for wintertime.  Perhaps that extra height explains the abnormal number of contrails.

OK, second post, still testing.  1-2-3, 1-2-3.