Dull Altostratus-ee day yesterday, but big Pac storm continues to move toward Catalina!

That thick (likely more than 3 km, or more than 10,000 feet) and steady gray sky diet of Altostratus opacus clouds didn’t provide a lot of visual highlights most of yesterday, in contrast to the many Altocumulus flocculations of the day before.  An example of yesterday’s sky for most of the day:

3:50 PM. Altostratus opacus.
3:50 PM. Altostratus opacus.  Or is it? Not much going on here1.

Virga hung down here and there, and some radar echoes during the day suggested a sprinkle here and there reached the ground, but none here.

Later, as usually happens, the tops of the clouds lowered, as did the bases, and we had some pretty Altocumulus again, some with long trails of virga, indicating a deep moist layer below cloud bottoms. For a time, as dewpoints rose, it looked like Ms. Lemmon might be topped with Sc, but those lowest clouds did not get quite low enough.

5:14 PM
5:14 PM.  Two layers of Altocumulus are present, the lower one having spires (Ac castellanus).  Nice lighting on mountains.

 

5:08 PM

5:08 PM. Two layers of Altocumulus are present, the lower one having spires (Ac castellanus), to repeat.

 

6:23 PM. Heavy virga issues from an old Altocumulus cloud, its once higher, pyramidal top has collapsed as snow developed in it and in essence, hangs down in an upside down version of what it once was
6:23 PM. Heavy virga issues from an old Altocumulus cloud, its once higher, pyramidal or mounding top has collapsed as snow developed in it and in essence, hangs down in an upside down version of what it once was (though not as tall as the virga is long here).
The Tucson balloon sounding (rawinsonde) for 5 PM AST (launched about 3:30 PM, rise at about 1,000 feet a minute.) BTW, takes about an hour and a half to get the whole depth normally measured, to around 100, 000 feet. During that time, or even during the first hour, the atmo is changing, so when its at 40,000 feet, what is measured at 3,000 feet isn't the same anymore. Introduces slight error into models into which these data get fed. Models think its an instantaneous view of the atmo over Tucson. I think you should know this.
The Tucson balloon sounding (rawinsonde) for 5 PM AST (launched about 3:30 PM, and rise at about 1,000 feet a minute.) BTW, takes about an hour and a half to get the whole depth normally measured, to around 100, 000 feet. During that time, or even during the first hour, the atmo is changing, so when its at 40,000 feet, what is measured at 3,000 feet isn’t the same anymore. Introduces slight error into models into which these data get fed. Models think its an instantaneous view of the atmo over Tucson at 5 PM AST (00 Z time). I think you should know this. Note tops of that Ac with heavy virga were about -30 C (-22 F)!  Notice, too, that some of those higher, colder Altocumulus flakes are not showing virga in the sunset photo above.

Weathering just ahead….

Rain One (“Little Bro”) is moving onto California coast as I write.  Residents in towns like the very-expensive-to-live-in Monterrey rejoicing as drops patter on rooftops now!  The negative news here is that the Canadian model has lessened the area of rain in Arizona as Rain 1 passes over us, confines the rain to central and northern AZ mountains now, still light, but not as widespread as before.

At the same time,  the US WRF-GFS model has been adding rain in AZ from Rain 1; previously it had NONE.  Now, these mods have now come together over us2 to quote a song title from the last century, both showing about the same thing, so that’s probably what will happen.  Just rain to the north of us.  So, a little less of a close call to Catalina  tomorrow as Rain 1 goes by.  Just middle and high clouds for us, and probably some virga, nice sunrises and sunsets.

Rain 2, “Big Bro” moves into southern Cal tomorrow night, and still looks like a real and necessary pounder for southern Cal before moving on and drenching little Catalina.  Will report on those SC amounts to see how big they get, too.

Rain should be falling here in Catalina by Saturday dawn and continue all day.  Range of amounts, still a not-so-great quarter inch on the bottom (if things don’t go well), but top (if things go really well) still an inch!  How great would that be?  So, best guess about 0.60 inches here in Catalina, from averaging those two “extrema.”  Later today, our U of AZ Beowulf Cluster model computations will start to have some quantitative amounts from actual calculations, not just a SOP guess from yours truly.  Check here at the U of AZ later in the day for accumulated totals based on this morning’s 5 AM AST data.

Way out there

While our drencher on the weekend seems to be a one-shot wonder for at least a week after it passes, the longest view from our WRF-GFS, valid way out on March 13 at 5 PM AST, 360 h from last night’s model run, has another major storm moving into the SW, but this time it doesn’t come from the west, but from the NW.  This is a climatological norm;  storms tend to move from NW to SE during the spring months in the western US, and so there’s SOME climatology to hang your hat on that the rain forecast below for us may be a real event, not a fantasy storm,  as so often happens that far into the future in our models.  See the map below, from IPS MeteoStar’s rendering of the WRF-GFS to brighten your day that bit more, knowing one good rain is coming, and maybe, just MAYBE, the pattern is shifting to a normal one with an occasional rain here in Catalina beginning after mid-March.

Valid at 5 PM, March 13. Green areas denote those regions where the model thinks it has rained during the prior 12 h.
Valid at 5 PM, March 13. Green areas denote those regions where the model thinks it has rained during the prior 12 h.

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3:50 PM. Actual Altostratus opacus. I've been talkin' clouds here for quite awhile, and in a clever kind of a test, wanted to see if you could tell the difference between the side of my gray car and an Altostratus cloud.
3:50 PM. Actual Altostratus opacus. I’ve been talkin’ clouds here for quite awhile, and in a clever kind of a test, wanted to see if you could tell the difference between the side of my gray car and an Altostratus cloud.  Its pretty important to me that you get this right.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

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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.