Loud May rain totals 0.47 inches in Sutherland Heights, Catalina

After last evening’s surprisingly heavy rain, we have now met our average for May for Catalina, having received 0.47 inches of rain over the past 24 h, some 0.36 inches during some house-shaking thunderclaps last evening.

Below are the 24 h local totals, ending at 4 AM today from the Pima County ALERT gauges rolling archive , these totals pretty much capturing all of our beautiful storm:

    Gauge    Location
    —-     —-       —-        —-       —-         —-       —————–            ———————
Catalina Area
    1010     0.63      Golder Ranch                            Horseshoe Bend Rd in Saddlebrooke
    1020     0.83      Oracle Ranger Station          approximately 0.5 mi SW of Oracle
    1040     0.55      Dodge Tank                   Edwin Rd 1.3 mi E of Lago Del Oro Parkway
    1050     0.75      Cherry Spring                approximately 1.5 mi W of Charouleau Gap
    1060     0.79      Pig Spring                   approximately 1.1 mi NE of Charouleau Gap
    1070     0.39      Cargodera Canyon             NE corner of Catalina State Park
    1080     0.63      CDO @ Rancho Solano       CDO Wash NE of Saddlebrooke
    1100     0.35      CDO @ Golder Rd              CSO Wash at Golder Ranch Dr

Santa Catalina Mountains
    1030     1.18      Oracle Ridge                 Oracle Ridge,  1.5 mi N of Rice Peak
    1090      0.35      Mt. Lemmon                   Mount Lemmon
    1110      1.34      CDO @ Coronado Camp          CDO Wash 0.3 mi S of Coronado,       1130          0.83      Samaniego Peak               Samaniego Peak on Samaniego Ridge
    1140      0.79      Dan Saddle                   Dan Saddle on Oracle Ridge
    2150     0.24      White Tail                   Catalina Hwy 0.8 mi W of Palisade RS
    2280     0.24      Green Mountain               Green Mountain
    2290      0.12      Marshall Gulch               Sabino Creek 0.6 mi SSE of Marshall Gulch

For more rainfall info, go here and here.  And here to the USGS, too, not to mention the NWS rainfall tables.  Too bad they can’t all be in one gigantic table!

The clouds and weather just ahead

A little cold morning rain, and even snow on The Lemmon, is looking likely for Saturday morning.  Presently, the core of the jet stream at 500 millibars or around 18,000 feet associated with a  mighty upper cold low that sits on Arizona on Saturday is forecast to be south of us (as was yesterday’s jet), a pretty black and white discriminator for cool season (Oct-May) rain here.

However, if that jet core around the low does not circumscribe TUS, you can forget rain.  From IPS MeteoStar, this rendering of the upper level configuration for Saturday morning, showing that it WILL circumscribe TUS:

The 500 mb heights and winds predicted for 5 AM AST, Saturday morning, May 10th. Its gonna a cool Mom's Day, too.  One would expect rain here in Catalina with this configuration.  Note how max winds are in a band well south of us.  That banding circumscribes the deeper parts of the Pacific moisture that came in with this trough.
The 500 mb heights and winds predicted for 5 AM AST, Saturday morning, May 10th. Its gonna a cool Mom’s Day, too. One would expect rain here in Catalina with this configuration. Note how max winds are in a band well south of us. That banding circumscribes the deeper parts of the Pacific moisture that came in with this trough.  This rendering is from the global crunch of data taken at about 5 PM AST, yesterday evening.  These runs are updated every six hours.

In the meantime, “troughiness” today,  tomorrow and Thursday, with secondary jet stream to south of us,  will give us some more photogenic high-based  Cumulus, maybe with some with virga in the afternoons.    Today, as our upper low says goodbye, subsiding air is supposed to keep clouds from attaining tops high and cold enough to form ice.   So, no rain today.

Yesterday’s clouds (going deep, as in pedantically)

There were some great scenes yesterday, summer-like ones, odd for May here, with massive rainshafts as the cloud bases lowered, reflected a huge jump in surface dewpoints to summer-like values in the mid-50s.  Cloud bases yesterday morning, riding the tops of Samaniego Ridge, were near 7 C, compared with -5 C the afternoon before.

This warming of  cloud bases greases the precipitation “wheel” since clouds with warm bases are be able to rain easier than ones with cold bases (say, near or at below freezing temperatures).   Droplet sizes have to be larger at any given level above cloud base compared to the clouds of the day before since more moisture is forming in those updrafts at the higher base temperature.    And, oddly, the larger the droplets, the higher the temperature at which ice can begin forming in clouds.    And when ice forms, snow, then rain, come out the bottom.

To go on too long on this in covering all rain possibilities for yesterday,  a base temperature of 7 C here is on the edge of being able to produce droplets big enough so that some begin colliding with one another and sticking together so that drizzle, then raindrops can form, a couple to a few thousand feet above cloud base, and those sizes of drops can really accelerate the formation of ice and then rain out the bottom.  Are there any readers left?  I doubt it.

Let us go even deeper….  It was hazy, smoky looking yesterday most of the morning, even when some good thunderstorms formed.  So what?  Well, smoke is bad for storms.  Remember when it was reported by Warner and and the U of Arizona’s own Sean Twomey (1967) that sugarcane burning made it stop raining downwind from those fires in Australia?   That effect has been verified in satellite measurements by cloud seeding nemesis, Danny Rosenfeld2 of the HUJ in Science a few years ago.

Well, too much smoke can choke droplet sizes down and inhibit the formation of rain by collisions, and delay the formation of ice.   And so we had that counter effect of smoke from somewhere, maybe LA this time since it was in the boundary layer, not aloft like that smoke layer from Asia was a couple of weeks ago.

So, cloud microstructurally-spekaing, it was an especially interesting day, one, if he were cloud maven person, wishes he would have had an aircraft to sample them.

But let us look now and see what all the fuss is about:

5:40 AM.  Dewpoints in the 50s, Stratocumulus clouds top Samaniego Ridge!
5:40 AM. Dewpoints in the 50s;  Stratocumulus clouds top Samaniego Ridge!
6:41 AM. Soft-serve Cumulonimbus forms over west Tucson, Oro Valley. Icy top looks like its comprised of needles and hollow sheaths to me, ice that forms at relatively high temperatures for ice formation, higher than -10 C.
6:42 AM. In the meantime, drama over Oro Valley to the west and north of Catalina as a deeper cloud unloads. Thunder, too.
7:19 AM. Haze and rain. This was a pretty astounding sight, so much haze/smoke in the rain as evidenced by these intense crepuscular rays.
8:19 AM. A real summer-looking sky on a big rain day. Frequent lightning was emitted by this behemoth that went on to pound Saddlebrooke.
8:37 AM. Unusually strong May thunderstorm pounds Saddlebrooke.

3:42 PM.  In spite of lots of convection and scattered Cumulonimbus clouds, the sky remained almost an eastern whitish due to smoke.
3:42 PM. In spite of lots of convection and scattered Cumulonimbus clouds, the sky remained almost an eastern whitish due to smoke, which I will blame on southern California, absent any facts or investigation.  No time.
6:59 PM. Our major evening rain and thunderstorms were developing upstream.

The End




1Warner, J. and S. Twomey, 1967: The Production of Cloud Nuclei by Cane Fires and the Effect on Cloud Droplet Concentration. J. Atmos Sci., 24, 704–706.

2Rosenfeld a “nemesis?”    See  the references and discussion below for kind of an interesting science story aside….

Rangno, A. L., and P. V. Hobbs, 1997a: Reply to Rosenfeld. J. Appl. Meteor., 36, 272-276, and…..

Rangno, A. L., and P. V. Hobbs, 1997b: Comprehensive Reply to Rosenfeld, Cloud and Aerosol Research Group, Department of Atmospheric Sciences, University of Washington, 25pp.

With the publication of voluminous (en toto) commentaries/critiques in 1997 by a few of our peers, but mainly by Danny Rosenfeld of the Hebrew University of Jerusalem, that concerned our 1995 paper reanalyzing the Israeli randomized experiments, yours truly and Peter V. Hobbs,  had attained, according the the Technical Editor of the Journal, the status of having become the most criticized meteorologists in the history of weather–well, in the history of the Amer. Meteor. Soc. journals, anyway!  How fun is that?  Its fun.

Our findings, that the two benchmark Israeli randomized cloud seeding experiments conducted in the 1960s and 1970s were largely misperceptions of cloud seeding effects due to storm biases on seeded days,  were independently verified in peer-reviewed publications by researchers at Tel Aviv University some many years later.

Operational cloud seeding has ended in Israel in favor of more fruitful avenues for obtaining the water they so badly need.

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.