Big virga, but no drops here

Flash:  Plethora of storms lining up for Catalina  during the rest of December.  Spring wildflower seeds take note.  Expecting to see a little snow here, too, in one of those–happens about once a year at our elevation (3,000 to 3500 feet), btw, so its not terribly unusual.)

The first one, on December 12th, is in the bag, the one we’ve talked about for a few months I think (that forecast based on spaghetti), except now it happens on the 13th.  Droughty Cal will get slammed by this one, too.

Hope you’re happy now.

—————————————————————

Now, for the “main event,” a recapitulation yesterday’s clouds….

A Nice,cool and gray day it was, if you like sky-covering layers of Altostratus translucidus and opacus , interrupted in the mid-day hours by a lower layer of Altocumulus clouds.

Those Altocumulus clouds represented  a “thin” corridor of clouds between deeper bands that went over us yesterday.   Bands of thicker and thinner clouds are pretty normal as storms pass by us.  First, this overview from satellite of our cloud sequence:

Visible satellite image for 1:15 PM yesterday when Altocumulus clouds comprised the main deck, rather than Altostratus
Visible satellite image for 1:15 PM yesterday when Altocumulus clouds comprised the main deck, rather than Altostratus.  Too bad there was more humidity underneath this system,; coulda been a great rain.  The arrow points to our location and the thinner cloud corridor that pass over at that time.  Cloud banding like this always occurs with storms, providing lighter and heavier periods of rain over an hour or two.

From the beginning, these for your edification:

9:29 AM. Classic icy Altostratus translucidus. No droplet clouds evident. Hope you logged that remark.
9:29 AM. Classic icy Altostratus translucidus. No droplet clouds evident. Hope you logged that remark.  Estimated height above ground?  22, 000 feet at this time, somewhat lower than the balloon sounding indicated at 5 AM AST.  Stuff lowers with time as storms approach.

 

11:29 AM. Big virga rolls in from the horizon. Lots of weak radar echoes beginning to show up in our area.
11:29 AM. Big virga (falling snow)  from Altostratus opacus (sun’s possible  is not detectable  at this time)  rolls in from the horizon. Lots of weak radar echoes beginning to show up in our area. Some lower flakes of Altocumulus clouds can be seen at left center, and on the horizon, left center.  Bases now around 18,000-20, 000 feet above the ground.  Likely a few drops were reaching the ground where the virga hangs down another few thousand feet.  Freezing level was around 11,000 feet above sea level.
1:40 PM. Thin spot in satellite image, characterized by Altocumulus opacus clouds, now passing over our area between bands of heavy Altostratis with virga.
1:40 PM. Thin spot in satellite image, characterized by Altocumulus opacus clouds, was now  passing over us between bands of heavy Altostratus with virga.  As a CMJ, the appropriate thing to say to your neighbor would have  been, “Wow (lot of excitement here), what happened to those deep clouds?!  Cloud tops have really come down.  Must be a thin spot.  Hope  that darkness on the horizon is another deep cloud band because then it might rain.”  End of excitement.  Cloud bases as you would guess, have continued to lower (but not nearly as much as the tops did).  The Altocumulus bases here are estimated to be 12,000 feet above the ground.  (By the end of the day, they were about 9, 000 feet above the ground, 12,000 feet above sea level).

 

3:05 PM. That last banded feature in the sat image, consisting of Altostratus opacus again, is starting to pass overhead. More weak radar echoes were present, some passing overhead, but, saw no evidence of a single drop on trace detector (car parked out in the open, moved for that purpose, since CM can't be outside at all times.
3:05 PM. That last banded feature in the sat image, consisting of Altostratus opacus again, is starting to pass overhead. More weak radar echoes were present, some passing overhead, but, saw no evidence of a single drop on trace detector (car parked out in the open, moved for that purpose, since CM can’t be outside at all times.
3:06 PM. Most of you will share my excitement here; surely a drop will be felt at any moment! As you know, in these situations, the rain hits the ground (largest drops first) long after the preciping part of the cloud has passed overhead. So, here we are looking downwind over the Charoulou Gap at a bunch of virga that passed over a few minutes ago, hoping for that drop that never came.
3:06 PM. Most of you will share my excitement here; surely a drop will be felt at any moment! As you know, in these situations, the rain hits the ground (largest drops first) long after the preciping part of the cloud has passed overhead. So, here we are looking downwind over the Charoulou Gap at a bunch of virga that passed over a few minutes ago, hoping for that drop that never came.
5:01 PM. As the deep cloud tops moved away, and a large clearing approached from the west, the setting sun provided a golden view of Samaniego Ridge. The lower-topped Altocumulus clouds can be seen above Sam Ridge. Bases were now down to 9,000 feet above the ground. Tops were about 16, 000 ASL, about -13 C. Higher colder tops were still in the area producing virga.
5:01 PM. As the deep cloud tops moved away, and a large clearing approached from the west, the setting sun provided a golden view of Samaniego Ridge. The lower-topped Altocumulus clouds can be seen above Sam Ridge. Bases were now down to 9,000 feet above the ground. Tops were about 16, 000 ASL, about -13 C. Higher colder tops were still in the area producing virga.

 

5:03 PM. Even the teddy bear cholla, horrible as it is, can be quite gorgeous in the evening light.
5:03 PM. Even the teddy bear cholla, as horrible as it is, can be quite gorgeous in the evening light.
5:19 PM. Later, sunset occurred, pretty much on time. It was OK. These, of course, are those Altocumulus clouds, sans virga, too warm for ice production even with tops around -13 C, around 10 F.
5:19 PM. Later, sunset occurred, pretty much on time. It was OK. These, of course, are those Altocumulus clouds, sans virga;  too warm in this case for ice production even with tops around -13 C, or about 9 F.  Ice formation characteristics can vary from day to day, the reason is not always clear, but seems to be most closely related to the sizes of the cloud droplets.  The bigger they are, the higher the temperature at which they freeze.

Below, from Intellicast, folks who hate Accuweather, where our radar network thought it rained a few drops on you (or probably just above you) yesterday:

Radar-derived precipitation for the 24 h ending at 5 AM AST this morning. Note dry slot over Catalina.
Radar-derived precipitation for the 24 h ending at 5 AM AST this morning. Note dry slot over Catalina.

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.