Mediocre clouds followed by a brilliant sunset

In case you missed it, this eye-candy from last evening as a crepuscular ray highlight some lower Altocumulus below the main layer:

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6:40 PM. Lower patch of Altocumulus is under lit by a ray of sunlight. Higher layer would be termed Altocumulus opacus. This was quite a dramatic scene and had to sprint up a hill from a neighbor’s place to get this and the next shot.
6:42 PM. Was gasping after sprinting up hill in an obsessive-compulsive pulse to get this shot. But it was worth it.

 

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11:19 AM. Small Cumulus were erupting nicely over Mt. Lemmon and the Catalinas, but oddly, due to the southeasterly winds aloft, they were larger in an extended cloud “street” downwind. See next shot taken at the same time.
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11:19 AM. That cloud street went for miles!

Now, for the rest of the day.  The Cumulus clouds with tops flattening into Stratocumulus were a bit disappointing, their tops, in a few places,  did reach the level where ice would form in them and virga and a few light rainshowers fell out.  Remember, gotta have ice to have precip is Arizona, mostly.

1:21 PM. Larger patch of Cumulus, spreading out due to a "stable layer" has reached upward to begin forming some ice. That fallout of ice is causing the base to look a little too smooth. If you can detect this, you have reached the pinnacle of cloud maven-ness.
1:21 PM. Larger patch of Cumulus, spreading out due to a “stable layer” has reached upward to begin forming some ice. That fallout of ice is causing the base to look a little too smooth. If you can detect this, you have reached the pinnacle of cloud maven-ness.  Its just beginning to come out, very hard to detect at this point, more obvious in minutes.  Even I wasn’t sure at this point, but hedged an opinion about it to myself.

 

1:42 PM. Same patch trailing ice, though not much. Still a difficult proposition to see it.
1:42 PM. Same patch trailing ice, though barely. Still a difficult proposition to see it.  Its just SLIGHTLY frizzy/fuzzy at the bottom, a look due to low concentrations of single crystals and a few snowflakes.
2:08 PM. Now the presence of ice is obvious. You have a wonderful itty-bitty rain shaft reaching the ground, and an ice veil around the edges of this cloud. Even a little baby could see that there was ice now.
2:08 PM. Now the presence of ice is obvious. You have a wonderful itty-bitty rain shaft reaching the ground, and an ice veil around the edges (upper left)  of this cloud. Even a little baby could see that there was ice now.  But as little and as long as it took to form and fallout, you would guess that the top was marginally cold for ice formation, a superb scenario for research aircraft.  From last evening’s TUS sounding, looks like they were barely ascending past the  -10 C  (14 F) level, maybe to -12 C to -13 C here in those tops that overshot a little inversion at -8 C.  Those flat-topped Altocumulus clouds that rolled in during the evening as the sun set had tops around -8 C, just a little too warm for ice to form in them.
3:27 PM. But that TUS sounding was not indicative of the air just a 100 or so miles south of us where large and deep Cumulonimbus arose. Can you see a Cb calvus top in this photo? It was pretty exciting to think that air capable of producing large storms was so close after it looked for awhile like a longish dry spell. The moisture was returning faster than models foretold a few days ago.
3:27 PM. But that TUS sounding was not indicative of the air just a 100 or so miles south of us where large and deep Cumulonimbus arose. Can you see a Cb calvus top in this photo? It was pretty exciting to think that air capable of producing large storms was so close after it looked for awhile like a longish dry spell. The moisture was returning faster than models foretold a few days ago.
3:26 PM.
3:27 PM Zoomed view of distant Cumulonimbus calvus top, far easier to see without the smog of the day before!

Today, the inversion is gone, and dewpoints are increasing all over southern Arizona as we start into a real tropical push. So chances of rain here in Catalina are zooming upward.  Should be some nice “Cbs” around.

Tropical storm Lorena is headed toward the tip of Baja and its remnants will come into southern California and Arizona over the next few days.  Hang on for some potential mighty rains, something to bring our summer rain season totals to more respectable levels here in Catalina.  Very excited, as are all local weather folk!

Also, no end to summer rain season yet appearing in mod run extending out for two weeks (from last evening’s global data crunch).  Still seems to hang on, for the most part, through the 20th of September.   Excellent.

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.