About real clouds, weather, cloud seeding and science autobio life stories by WMO consolation prize-winning meteorologist, Art Rangno
Light shower with graupel falls on Catalina Mountains!
Happened around noon yesterday. I could see it from here that the shaft consisted of graupel mixed with some rain. Nice video of this exceptionalism-of-the-day event here from the U of AZ.
Its interesting to me, and to you, too, most likely, was that yesterday it was asserted here that there would be no ice in the “small” Cumulus clouds that were expected to form during the day. And yet we had a momentary Cumulonimbus cloud with a ton of ice and a graupel/rain/snow shaft! Huh.
In related1 distractive headlines:
Fields of gold erupt in Catalina!
Hours: 10 AM to 3 PM, M-S, otherwise closed. Why do they do that? You won’t find the answer here, so move along now…
4:00 PM yesterday, on hills west of Spirit Dog Ranch. Numerous poppy flourishes in this area. On horseback,, Nora Bowers, co-author of the popular guide, Wildflowers of Arizona. Those poppy blossoms were pretty much closed here. You really should get out and see them if you can. Well, worth it.
Rasslin’ Dogs!
“Emma” border collie, bottom, “Banjo”, border terrier mix of some kind, top. 2-day old distractive photo. More distraction. Few readers will likely go farther than this….
Yesterday’s clouds and explanations
8:22 AM. Altocumulus, bases about 14, 000 feet above sea level, or about 11,000 feet above the ground here in Catalina. The temperature at cloud top, via the TUS balloon sounding, was about -15 C (5 F), pretty cold for not having some virga or ice showing. It happens. There could be several reasons: Lack of ice nuclei in that layer? Tiny droplets, ones that resist freezing more than larger cloud drops? Lack of mixing with very dry air above cloud top (it was moist all the way up to Cirrus levels))? Mixing in very dry air at cloud top can lower the temperature of a drop a few degrees before it disappears completely, thus increasing the chance that it will freeze. That last effect is mostly operating in Cumulus clouds whose tops can penetrate relatively far into very dry layers. So, once again, we have no real answers, or maybe, all of them. It is worth noting that going to -15 C here and no ice in a Cumulus cloud is a virtually unknown occurrence, one that speaks to ice nuclei, those specks of mineral dirt that are known to cause ice to form in clouds, like kaolinite, etc. originating in the boundary layer/dirt interface being a primary culprit.
10:49 AM. In fact (!), “small” Cumulus clouds DID form yesterday, hold the ice. Quite a forecasting triumph.10:51 AM. While small Cumulus clouds pervaded the sky, there was an exception; the usual cloud street that forms off the Tortolita Mountains was trailing over Catalina and those clouds in it were at least of mediocris size (likely a km deep or so), and due to the low freezing level yesterday, getting close to the ice-forming level for Cumulus clouds here of around -10 C (14 F). Was actually outside, as you probably were, too, as it passed over, shifting gradually to the south, hoping for a drop so’s I could report a trace of rain today. “Great weather folk don’t miss traces!” (Dry-fit tee shirt in preparation….)11:00 AM. I want to keep reminding you of the prevalence of small, “docile” Cumulus clouds (ignore large dark cloud shadow at left). Just trying to balance out the cloud day picture the way media balances things out, regardless of whether they are Democrats or Republicans.
11:52 AM. Graupel begins to fall from a Cumulus congestus just beyond Pusch Ridge. It would be hard to describe the magnitude of the embarrassment I began to feel having stated that there would be no ice. I realized I had been careless as a forecaster, not really looked hard enough at the conditions, the lapse rates. It was truly humiliating to see this happen. Oh, in case you can’t see anything, the next photo is a blow of this humiliation as it began to take place.11:58 AM. Picture of graupel particles emitting from a cloud from 10 miles away. Note fine strands, a sure sign of graupel especially on day with a low freezing level and cloud bases at below freezing temperatures. Note too, ice is not visible at cloud top, something that indicated an abundance of droplets over ice crystals in the cloud, the conditions that lead to the rapid formation of graupel (soft hail).
12:10 PM. More humiliation and graupel; a forecasting disaster is in progress for all to see!
12:17 PM. Turret at left side, under fragment, appeared to be softening to the look of an icy composition that all would recognize immediately, but external ice composition not apparent yet. Note the “harder”, more cauliflower look of the turret on the right half of the photo, indicating an all liquid external composition. Graupel was forming inside that right half, though.
12:29 PM. Total icy humiliation. The “cotton candy” transition of the prior turret to “Mr. Frosty” (left of center) was complete for all to see. Looking toward Catalina, I could almost hear the laughter, “Calls himself a ‘cloud-maven’, said there wouldn’t be any ice today, and look at all that ice! What joke!” Now that the turret has become a modest Cumulonimbus, likely completely glaciated, the precipitation falling would be snowflakes (not graupel since the liquid water droplets are gone inside it) melting into rain farther down.
4:21 PM. The clouds returned to their former “small”, ice-less, sizes for the rest of the day after the humiliating exception.
6:18 PM. Revealed in yesterday’s near cloudless sunset, undulations in the ever present high altitude haze layers that circumscribe our planet. Layers like this, that are featureless except for the revealing waves causing the undulations, are extremely old, days, and are often reffered to as long range transport events because they likely traveled thousands of miles before arriving over Arizona. They are likely to be composed of old, old contrail emissions, emissions that have worked their way up in the atmosphere from over heated land surfaces, distant forest fires, and so on.
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1Its not really related but sounds like something that should be said.
By Art Rangno
Retiree from a group specializing in airborne measurements of clouds and aerosols at the University of Washington (Cloud and Aerosol Research Group). The projects in which I participated were in many countries; from the Arctic to Brazil, from the Marshall Islands to South Africa.
12:29 PM. Total icy humiliation. The “cotton candy” transition of the prior turret to “Mr. Frosty” (left of center) was complete for all to see. Looking toward Catalina, I could almost hear the laughter, “Calls himself a ‘cloud-maven’, said there wouldn’t be any ice today, and look at all that ice! What joke!” Now that the turret has become a modest Cumulonimbus, likely completely glaciated, the precipitation falling would be snowflakes (not graupel since the liquid water droplets are gone inside it) melting into rain farther down.
