About real clouds, weather, cloud seeding and science autobio life stories by WMO consolation prize-winning meteorologist, Art Rangno
Iridescence, jet streak Cirrus warn of overnight “middlin'” storm
I guess “billows” (“undulatus” in cloudspeak) two days ago in the late afternoon wasn’t enough of a sign that the weather was changing. Yesterday we had fast moving Cirrocumulus with rainbows in it, and as the sun was setting, “jet streak Cirrus”, a line of Cirrus clouds often seen in the very core of high altitude, powerful jet streams passed overhead.
How hard was the wind blowing up there in that Cirrus last evening? Oh, our Tuscon balloon sounding, lifting off around 3:30 PM, going up about a 1000 feet a minute to, indicates that the max wind up there at Cirrus level was 146 knots (just under 170 mph)! Yikes. Poor balloon. Must be in France by now.
The storm has been a bit of a disappointment in rain production. We’ve only logged 0.22 inches1. Not as much as foretold here, 0.33 inches, but that forecast was a better prediction than by “Weather Underground Robotics” (0.58 inches). Its great to beat a robot!
We had another sign yesterday in the fastest moving Cirrocumulus clouds I think you’ll ever see around here (about 100 mph), ones at just 18,000 feet above sea level, 15 kft above Catalina: rainbows of color near the sun called iridescence (also called “irisation”). Here, as is the norm here, are a few too many shots of the same thing2.
10:54 AM. The fist of weather is used as a prop to indicate that these colors are forming a ring around the sun. Usually you try to find a light standard somewhere…maybe a “gopro cam on a stick” might do it. Just don’t look at the sun when you do this.10:57 AM.10:57 AM, pulling back some for perspective. As we often say here, “so pretty.” And look at how tiny the granulation is in this Cirrocumulus cloud is!
The colors themselves, of course, don’t warn of something about to happen, but the fast movement from the southwest did; a powerful jet stream is over you. That strong stream, the result of temperature gradients in the atmosphere, is dividing deep warm air from deep cold air, and steers the alternations of high and low pressure centers, and with those alternations of lows and highs along the jet stream, air is drawn from different latitude zones and the boundaries where those different masses of air meet at the surface, is called fronts. Here, such as last night, its nearly always cold ones.
The rest of the day was pretty exciting, the wind arising suddenly yesterday morning, along with our usual great visibility, and darker blue wintertime skies, made the clouds stand out more.
7:56 AM. Looking to the west at a scattering of Stratocu patches.7:57 AM. Highlight on the hills above Saddlebrook. Stratocumulus overhead.8:42 AM. This patch of Stratocumulus was the result of a lift zone that often produces clouds headed our way in southwesterly flow. The difference here is how limited in size this patch was allowing you to see where that lift zone was. Downstream, though, descending motions creamed this cloud, one that sat there most of the early part of the day. Usually a whole layer is over us, with a clearing visible toward the SW horizon.11:02 AM. Still out there pretty much near the same spot, still limited in size. Wind here now 20-30 mph with stronger puffs.
11:40 AM. By this time it had shifted closer to us, still forming on the southwest end, dissipating at the downwind end where the cloud is so ragged due to mixing with dry, descending air.12:42 PM. Creeping closer, but still a standing wave, dissipating as it came toward us. It was about this time that it disappeared, the sky becoming more complex with no simple standing waves.
The sky at last, considering the power of the trough approaching, FINALLY began to fill in. Started looking around for the first sign of ice having formed in these clouds as the air aloft became cooler. Along with this filling in by Cumulus and Stratocumulus clouds, some sun highlights began to appear on our mountains, contrasted by the darkening skies above.
1:55 PM. Stratocumulus clouds bank up against the Catalinas, Samaniego Ridge.2:03 PM. While Stratocumulus banked up against the mountains, huge temporary clearings occurred elsewhere. Notice how shredded the tops of these clouds are and how the tops lean to the right. They’re revealing the great increase in the wind with height, and yet, how dry it was above this layer (that, by the ragged cloud tops mixing with the very dry air just above them.)3:38 PM. Here comes the Jet Streak Cirrus! Also about this time, the frontal windshift line, marked by low scud clouds in the cold air, began to appear on the NW horizon. It was an exciting moment. Here we go! FROPA within a coupla hours maybe. Well, took longer than that….3:52 PM. A little ruffle of Cirrocumulus leads the advance of the jet streak Cirrus.4:11 PM. Cloud line forming above the frontal windshift line. Was progressing this way at this time, but was to stall, maybe back off.4:11 PM. Zooming, floating over Saddlebrooke, this close up of our FROPA and windshift line. Ended up backing off, dissipating, maybe reforming later after dark. These lowest clouds form in the colder air associated with the windshift line at the nose of the front as the moist air ahead of the front mixes with it and is lifted. We see this with most of our incoming cold fronts, and in our summer thunderstorms. The best cases form “arcus clouds”, a solid line just above and behind the windshift at the ground. These kinds of ragged clouds, in cloudspeak, are called “pannus.” Was pretty excited here, as no doubt you were, that FROPA (frontal passage) was imminent, might happen within the hour. Nope.4:40 PM. In the meantime, our jet streak CIrrus, above the Stratocumulus clouds, moved overhead, the clearing behind this thin band leading to some memorable fading sun highlights on the Catalinas.5:40 PM. No words needed.5:43 PM. “Fading sun and rain gauge.” Another one of those exceptional scenes you won’t find anywhere except on this blog. Tell your friends. A small mammal, termed a “packrat” is decimating my prickly pear wind protection for this gauge! A lot of rain loss occurs due to wind. drops missing the collector! It very upsetting to see this happen.5:43 PM. Even the often despised teddy bear cholla can be so beautiful in this fading sun, the spines capturing it so well.
Eventually our jet streak Cirrus provided the background for another great sunset scene:
5:56 PM.
A 300 millibar (about 30,000 feet above sea level) with an IR satellite image for yesterday at 5 PM AST. The Cirrus layer extended from about this height to around 35, 000 feet above sea level. according to our TUS balloon sounding. Arrows denoted the jet streak Cirrus cloud thatpassed over us, enhanced in the downwind region of the Baja mountains. Note that the wind at San Diego max wind was even slightly stronger than our wind max was at this level at152 knots. This map is the courtesy of the University of Washington Huskies Weather Department.
Today’s clouds and weather
From that map above, you’ll see that there’s a “tail-dragger” trough still to the west of us and about over Sandy Ego (haha). That’s going to keep the air over us extremely cold, and with some sun, the Cumulus clouds that arrive are expected to have tops colder than -15 to -20° C, plenty cold enough for the formation of ice.
Ice means precip, snow up there, rain down here in spots. So, we could still pick up a few more hundredths if a shower happens to drop by. The chance of isolated very light showers in the area is 100%, but no one can tell you if one will actually land on us. You’ll have to be watching, mostly after 12 noon. Look to the west toward the Tortolita Mountains, terrain that ought to spawn one or two of those.
Looks like a longer dry spell ahead; several days to a week, maybe more.
The End
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1CoCoRahs gauge, btw. NWS-style gauge had only 0.20 inches, likely due to enhanced wind loss associated with my collapsing prickly pear protector. 2 I was driving and had to park and jump out of car to get these. You only have seconds or maybe a minute or three to capture stuff like this.
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.
Great examples of iridescence, Art. I usually have to wait until later in spring or summer to see it here, though just 3 days ago I saw a good “mock sun”.
Hi, Roland,
Yes, after having lived in SEA for 32 years, I am sure you will not see much of the higher cloud cover until spring when the weather gets more showery with sun breaks, and lesser storms.
We see quite a few mock suns (sun dogs, parhelia) here due to the many days with passing cirriform clouds absent low cloud cover.
Great examples of iridescence, Art. I usually have to wait until later in spring or summer to see it here, though just 3 days ago I saw a good “mock sun”.
Hi, Roland,
Yes, after having lived in SEA for 32 years, I am sure you will not see much of the higher cloud cover until spring when the weather gets more showery with sun breaks, and lesser storms.
We see quite a few mock suns (sun dogs, parhelia) here due to the many days with passing cirriform clouds absent low cloud cover.
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