Traces of rain and a Lemmon rainbow

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6:25 AM. Altocumulus perlucidus. According to my cloud chart, informally known as “America’s Cloud Chart”, it could rain within 6 to 196 hours. Its quite useful.
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10:24 AM. Altocumulus opacus. Note the rumpled look of the sky. Indicates that the clouds are rather shallow and composed of droplets rather than a mix of ice crystals and droplets. However, if you strain your eyeballs and look to the horizon, you can see a smoothing and a little virga showing that the cloud tops are rising and they’ve gotten cold enough to produce ice. According to my cloud chart, when you see “Ac opacus” it could rain within 6 to 196 hours.
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1:44 PM. While the clouds are pretty much the same gray color as in the prior photo, they’re much thicker here and are “Altostratus opacus”. “opacus” because the sun’s position is not visible, though it wouldn’t be in this direction anyway, but to the right. The bottom of this is smooth due to widespread, light falling snow, though it not in a localized area enough to be called virga in this shot. The lack of bunched or heavy virga somewhere tells you that the cloud tops are pretty smooth, too, not a lot of variation in height.  The base is really determined by the point that you descend out of this precip, in this case up around 10 kft above the ground over Catalina.
4:12 PM. Altostratus opacus praecipitatio or Nimbostratus, either name will do. Recall the quirk in our cloud naming system that makes, "Nimbostratus" a middle-level cloud. The base of these clouds is the general level where the snow falling out has evaporated. Due to bulging tops, and stronger updrafts, a little of the precip was able to fall out because the snowflakes coming out the bottom had grown larger and were able to survive the dry air below cloud base.
4:12 PM. Altostratus opacus praecipitatio or Nimbostratus, either name will do. Recall the quirk in our cloud naming system that makes, “Nimbostratus” a middle-level cloud. The base of these clouds is the general level where the snow falling out has evaporated. Due to bulging tops, and stronger updrafts, a little of the precip was able to fall out because the snowflakes coming out the bottom had grown larger and were able to survive the dry air below cloud base.

Some rain fell about this time in Catalina.  Not enough to darken the pavement completely at any time.  The main thing to take away from that hour of very light rain is that it was not “drizzle” as even some errant meteorologists call such sprinkles.

You will be permanently banned from attending any future meetings of the cloud maven club if you refer to such rain as we had yesterday afternoon as “drizzle.”  Drizzle is fine (200-500 micron in diameter drops that are very close together and practically float in the air.  Because they fall so slowly, and are so small to begin with, you can’t have drizzle at the ground from clouds that are much more than a 1000 feet or so above the ground because as soon as they pop out the bottom, those drops start evaporating and fall slower and slower by the second, and in no time they can be gone even in moist conditions.  That’ s why its somewhat hilarious and sad at the same time,  when, in particular, military sites for some unknown reason, report ersatz “drizzle: (coded as L, or L-) in our hourly aviation reports from clouds that are based at 5000 feet or something CRAZY like that.

This band of Nimbostratus/Altostratus had a backside that approached as the sun went down, and as you know, that clearing let some sunlight enrich and dramatize the views of our beloved Catalina Mountains:

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5:39 PM.
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5:41 PM.

Finally, dessert:

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5:47 PM. Rainbow lands on the University of Arizona Wildcat’s Skycenter atop Ms. Mt. Sara Lemmon.
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5:48 PM.

The amazing rains ahead

Nothing that you don’t already know about, so no use me blabbing about it too much.  But in case you haven’t seen it, The Return of Joe Low (after over-hydrating over the warm waters of the eastern Pacific), is expected over the next couple of days, with a little help from another disturbance, to bring colossal rains to eastern Arizona and especially New Mexico.

Below, from our friendly U of  A Wildcat Weather Department a model run from yesterday’s 5 PM global data (the Wildcat’s downsize the US WRF-GFS model in this awesome depiction).

Check out the totals expected by the evening of October 23 rd.  Stupendous.  Usually these totals are a bit overdone, but even so…… Will take a nice bite out of drought.

Precipitation totals expected by 5 PM AST October 23rd. Looks something like a tie-dyed Tee.
Precipitation totals expected by 5 PM AST October 23rd. Looks something like a tie-dyed Tee.

The End

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.