About real clouds, weather, cloud seeding and science autobio life stories by WMO consolation prize-winning meteorologist, Art Rangno
Wintertime cold Cumulonimbus clouds erupt with sprinkles and snow flurries; no damage reported
One passed over at 9:19 AM with a hard multi-second, surprise rain shower. One person reported a couple of graupel, or soft hail particles. Tipped the bucket, too; 0.01 added to our Sutherland Heights storm total. Its now at 0.23 inches. Of course, there was no damage, but putting that word in a title might draw “damage trollers”, increase blog hits….
The rest of the day was clouds withering, getting mashed down on tops as bases rose and tops settled back, then suddenly, about 3:30 PM, small areas of ice crystals began to show up in a couple of spots, and, boy, did things take off after that. Tops were lifting to higher temperatures, likely due to an approaching trough, one that otherwise is too dry to do much else.
Honest to goodness cold, wintertime Cumulonimbus clouds formed, though not very deep ones. Probably of the order of 2-3 km thick is all (eyeball estimate).
But with our cold air aloft, tops were well below -20° C (4° F), lots of ice formed in them and produced streamers of ice and virga across the sky, and in tiny areas, the precip got to the ground.
And with “partly cloudy” conditions, there were lots of gorgeous, highlighted scenes around the mountains.
Let us review yesterday’s clouds and weather and not think about the future too much, starting with an afternoon balloon sounding temperature and dew point profile from IPS MeteoStar:
The Tucson balloon sounding (“rawinsonde” in weatherspeak) launched about 3:30 PM yesterday. Takes about an hour to reach 60,000 feet, but goes higher. Cloud bases were just about at the top of Ms. Mt. Lemmon. Tops were only around 18,000 feet above sea level, but were extremely cold for such small clouds. Hence, they were only about 9,000 feet thick at their maximum.
So what do clouds look like when they have tops as cold as -28°Ç?
Well, I really didn’t get a good profile shot of those clouds, they were either too close, obscured by other clouds, or too faraway, so instead let us look at two dogs looking at something as a distraction:
4:11 PM. Dogs observing a plethora of glaciating Cumulus clouds, transitioning to Cumulonimbus.
Well, let’s start this when the ice first appeared in a cloud, much later in time than what was thought here yesterday morning. If you logged this “first ice” you are worthy of a merit, a star on your baseball cap:
3:24 PM. FIrst ice of the day, finally, spotted on the SW and WSW horizon in two little areas. The file size is huge so that you can see it for yourself. I had just about given up on ice in clouds, Notice, too, how small the clouds are at this time.
Well, while flawed from a cloud profile sense, here’s what they were looking at, it was the best I could do:
4:19 PM. Note sunlit shower reaching the ground. The hazy stuff is ice crystals, a lot of them all over the place.4:22 PM. A close up in case you don’t believe me that the rain was reaching the ground. I sometimes find that credibility is lacking here.4:39 PM. Eventually a cluster of precipitating clouds developed near the Catalina Mountains and here are dropping snow and graupel trails.
Let us go zooming:
4:39 PM. Shaft up close. That dark, narrow line in the middle is without doubt a soft hail (graupel) strand. THere might be others, but this one is obvious. The “verticality” is due to faster falling particles comprising that strand, which graupel are because they are ultimately snowflakes that have captured cloud droplets on the way down, making them much heavier than just a snowflake.4:45 PM. Just light snow falling out here on the Catalinas, no real “verticality” in this shaft, which would be a sign of graupel falling out.4:46 PM. An opening allowed this zoomed cross section of a cold, wintertime Cumulonimbus (capillatus) cloud streaming a shield of ice and virga downwind. On the left sloping-upward part, the Cumulus turrets still contain liquid droplets (have that ruffled, hard look associated with the higher concentrations that go with droplet clouds compared to all ice clouds). Sometimes, in spite of the low temperature, here, from the sounding the top is likely approaching the minimum temperature of -28°C, droplets can still survive for a short time before freezing, giving way to lower concentrations of ice crystals. That appears to be the case here at the tippy top. of the cloud in the back What is interesting here, an enigma, is that the foreground cloud in front of the cloud I was just discussing, is clearly all ice from the smallest element to its top and mimics the cross section of the background cloud. Could it be that its simply older and ice generated in the colder regions has permeated the whole cloud?
Below, diagrammed:
Same photo with writing on it since the written explanation didn’t seem very satisfactory.5:07 PM. Graupel in the Gap (the Charouleau one). Well, maybe its a little beyond the Gap, but it sounded good to write that.. This started to fall out of a Cumulus congestus transitioning to a Cumulonimbus. The first particles out the bottom are always the heaviest, hence, graupel or hail.
Looking elsewhere, there are snow showers everywhere!
5:08 PM. Nice shafting over there near Romero Canyon. Pretty straight up and down, so likely has a lot of small graupel in it.5:08 PM. Looking down Tucson way, this is NOT a graupel shaft, but rather gently falling large snowflakes.. Sure the particles are large, but look at how they’re just kind of hanging there getting mixed around by a little turbulence, almost forming a mammatus look. There are likely aggregates of dendrites, fern-like ice crystals that grow like mad around -15° C, and because of being complex forms, often lock together when they collide. Its not unusual to have 20 or more single stellar. dendritic crystals locked into a single snowflake. Where the bottom disappears, likely around 3000 feet above sea level, is where those big aggregates are melting into rain drops.5:10 PM. Interrupting the tedium with a nice neighborhood lighting scene as a sun poked between clouds. We’re not completely cloud-centric here, but close.5:26 PM. This strange scene of a very shallow snow cloud, completely composed of ice and snow, obscuring the tops of the Catalinas, but being very shallow, hardly above them may explain the cross section enigma. The snow cloud here is all that remains of a much deeper cloud that converted to all ice, then those crystals just settling out, the whole cloud dropping down as a snow flurry. It may well have been as deep as the cloud top on the left or higher before converting to ice and just falling to the ground “en masse.” Or is it, “en toto“? What makes this odd is that there is usually some “cloud ice” (ice particles too small to have much fall velocity) at the level from which the precip fell from. You don’t see that here; just a belt of light snow. Maybe this is why there was that shallow, glaciated cloud in the Cumulonimbus cross section shot….. That shalllow cloud was not a new portion, but rather a tail dragger like this stuff, once having been much higher and was actually ice settling out, not new rising, glaciated cloud. From the back side, you can see that this ice cloud would appear to slope up if viewed from the east instead of the west like our cross section iced out cloud. Setting a record for hand waving today. IS anybody still out there? I don’t think so. Maybe I need another dog picture….5:34 PM. Here’s the last of that unsual snow cloud as its last flakes settled to the ground.
The day concluded with a very nice sunset:
5:53 PM. Sunset color with shafts of snow turning to rain down Tucson way.
Now, the long dry spell… Break through flow from the Pacific under the “blocking high” eventually happens about a week away now, but more and more looks like that flow might stay too far to the north of us, rather blast northern Cal some more, and not bring precip this far south. The blocking high needs to be in the Gulf of AK, but now is being foretold to be much farther north…
The End, gasping for air here. More like a treatise than a quick read!
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.
