April showers and why

From your Pima County ALERT gauges, these 24 h totals ending at 3 AM this morning (covers the whole storm):

Gauge                        24                Name                        Location
    ID#      minutes    hours      
    —-     —-       —-        —-       —-         —-       —————–            ———————
Catalina Area
    1010                   0.04      Golder Ranch                 Horseshoe Bend Road in Saddlebrooke
    1020                   0.20      Oracle Ranger Stati          approximately 0.5 mile southwest of Oracle
    1040                   0.08      Dodge Tank                   Edwin Road 1.3 miles east of Lago Del Oro Parkway
    1050                   0.20      Cherry Spring                approximately 1.5 miles west of Charouleau Gap
    1060                   0.55      Pig Spring                      approximately 1.1 miles northeast of Charouleau Gap
    1070                   0.08      Cargodera Canyon             northeast corner of Catalina State Park
    1080                   0.08      CDO @ Rancho Solano          Cañada Del Oro Wash northeast of Saddlebrooke
    1100                   0.04      CDO @ Golder Rd              Cañada Del Oro Wash at Golder Ranch Road

Santa Catalina Mountains
    1030                   0.75      Oracle Ridge                 Oracle Ridge, approximately 1.5 miles north of Rice Peak
    1090                   0.00      Mt. Lemmon                   Mount Lemmon
    1110                   0.75      CDO @ Coronado Camp          Cañada Del Oro Wash 0.3 miles south of Coronado Camp
    1130                   0.24      Samaniego Peak               Samaniego Peak on Samaniego Ridge
    1140                   0.83      Dan Saddle                   Dan Saddle on Oracle Ridge
    2150                  0.12      White Tail                       Catalina Highway 0.8 miles west of Palisade Ranger Station
    2280                  0.20      Green Mountain               Green Mountain
    2290                  0.24      Marshall Gulch               Sabino Creek 0.6 miles south southeast of Marshall Gulch

The absence of precip at Mt. Lemmon is not because the storm went around it, but rather because it fell as snow.

Here in the Heights, 0.08 inches fell between 1 PM and 3 PM.  Clouds accompanied the rain.

But what kind?  That’s why I am here for you.  See way below.

First, some techno-babble.   Rain was an on and off event for Catalina and environs in the models run after run.  A forecaster friend sent many e-mails that went from “looks good for rain” here, and just about as many that said,  “doesn’t look good for rain.”  In fact, the (WRF-GFS) model run for just 12 h before it rained, had no rain here, but just a bit to the north.  What happened?

Extra sag.

Here’s the amount of trough “sag” (“amplitude”, as we would say) over Arizona predicted just 14 h before it started raining in Catalina yesterday afternoon:

12 forecast valid for 11 AM yesterday morning. Note that the wind maximum is NORTH of Catalina, and over central AZ.
12 forecast valid for 11 AM yesterday morning. Note that the wind maximum is NORTH of Catalina, and over central AZ.

 

Areas of rain forecast to fall in the 6 h ending at 11 AM AST yesterday morning.
Areas of rain forecast to fall in the 6 h ending at 11 AM AST yesterday morning.  Rain just a tad north of Catalina.
A computer analysis of the actual winds at 5 PM AST yesterday showing that the trough had more amplitude (sag, droop, etc.) as it crossed Arizona yesterday than was forecast just a day or so in advance. That meant we in Catalina were more embedded in the deeper, and colder clouds with this trough. The jet stream circumcribes those clouds during the cool season here in AZ and most of the SW US.
A computer analysis of the actual winds at 5 PM AST yesterday showing that the trough had more amplitude (sag, droop, etc.) as it crossed Arizona yesterday than was forecast just a day or so in advance. That meant we in Catalina were more embedded in the deeper, and colder clouds with this trough. The jet stream circumcribes those clouds during the cool season here in AZ and most of the SW US.  See rain totals at top of blog.

In case you think I am lying again, just because I am a meteorologist and say a lot of wrong things, below is the REAL map for last evening with wind data from rawinsonde balloons on it.

From the Huskies, this 500 mb map over satellite imagery. Strongest winds in our trough run from San Diego, Tuscon, to El Paso, with the tightest spacing of contours and strongest winds at this level in extreme northern Mexico
From the Huskies, this 500 mb map over satellite imagery. Strongest winds in our trough run from San Diego, Tuscon, to El Paso, with the tightest spacing of contours and strongest winds at this level in extreme northern Mexico

I hope you’re happy now.

Here’s what the temperature did as the windshift and rain began, in case you missed it:

Yesterday's temperature trace for Sutherland Heights.
Yesterday’s temperature trace for Sutherland Heights.

 

Yesterday’s clouds

The sequence:  cloudy, sunny “sucker hole” (one of Biblical proportions), cloudy, raining, sunny, dusty.

6:06 AM. Altostratus and Cirrus combine to produce a gray sky.
6:06 AM. Altostratus and Cirrus combine to produce a gray start to the day.
9:44 AM. Lower level moisture layer produces an Altocumulus lenticularis just beyond Pusch Ridge. Seems sky will cloud up real good at this point.
9:44 AM. Lower level moisture layer produces an Altocumulus lenticularis just beyond Pusch Ridge. Seems sky will cloud up real good at this point.
Also at 9:44 AM. Looks real bad off to the N, too, in dense Altostratus and lower Sc or Ac.
Also at 9:44 AM. Looks real bad off to the N, too, in dense Altostratus and lower Sc or Ac.

 

 

10:57 AM. Sucker hole! Its real sunny, warming up. You're thinking as you ride your horse as I was, "What a bad weatherman we have! Said would be windy, cold, and might rain, and yet here is the sun and warmth. What a bad weatherman we have!"
10:57 AM. Sucker hole! Its real sunny, warming up. You’re thinking as you ride your horse as I was, “What a bad weatherman we have! Said would be windy, cold, and might rain, and yet here is the sun and warmth. What a bad weatherman we have!” (Weatherman is laughing in the background.)
11:44 AM. Sucker hole starts to fill in... Haha!
11:44 AM. Sucker hole starts to fill in… Haha!  “Dreamer” is the horse there.
12:10 PM Sucker hole filling in!
12:10 PM Sucker hole filling in more and more!  You’re starting to feel real bad that you made fun of your weatherman, but he’s still laughing at you.

 

 

 

 

 

 

 

 

 

 

1:17 PM. Rain showing up to west-southwest, upstream. Wind shift hits and ten degree cool off begins. You're glad you finished your horseback ride none too soon.
1:17 PM. Rain showing up to west-southwest, upstream. Wind shift hits and ten degree cool off begins. You’re glad you finished your horseback ride none too soon.
3:54 PM. A remarkable thing is happening. While there's plenty of dust in the air. it is also still raining slightly, almost from drizzle-sized drops. Eyeballig the cloud depth of the backside of the raining clouds from which the drops MAY have fallen from, CM opines that these drops are comprised of melted aggregates of needle or sheath ice crystals that were, as single crystals before aggregating as they do when in high concentrations, were really in high concentrations in those clouds, implying a strong ice multiplication phenomenon was at work. Was really a weird scene to have so much SUN and drops falling from clear sky overhead. I would be very proud of you if you noticed this few minute event at the end of our little rain.
3:54 PM. A remarkable thing is happening. While there’s plenty of dust in the air. it is also still raining slightly, almost from drizzle-sized drops. Eyeballing the cloud depth at the backside of the rainband clouds from which the drops MAY have fallen from, your CM opined that these drops originated with melted aggregates of needle or sheath ice crystals that, as single crystals before aggregating,  were in high concentrations (10s to 100s per liter) in those clouds, implying that a strong ice multiplication phenomenon was at work inside them. Was really a weird scene to have so much SUN and drops falling from clear sky overhead. I would be very proud of you if you noticed this few-minute event at the end of our little rain.

 

 

Rawinsonde balloon temperature and dewpoint profile near the time that it rained in clear air from the backside of our rainband. As you can see, cloud tops were around -10 C or a little cooler, pretty warm for raining clouds here. The main part of the rainband likely had somewhat cooler cloud tops. Thought you like to know. This sounding supports the idea that an ice multiplication process was at work, at least on the back shelf of these clouds that rained.
Rawinsonde balloon temperature and dewpoint profile near the time that it rained in clear air from the backside of our rainband. As you can see, cloud tops were around -10 C or a little cooler, pretty warm for raining clouds here. The main part of the rainband likely had somewhat cooler cloud tops. Thought you like to know. This sounding supports the idea that an ice multiplication process was at work, at least on the back shelf of these clouds that rained. I wanted to confirm prior ground speculations with more speculations from the sounding at rain time, though it was launched around 3:30 PM AST way over there by Davis Monthan Airbase. Wondering now if I will finish this blog today….
4:34 PM. Shelf of rainband exits the Catalinas. Nice lighting, though.
4:34 PM. Shelf of rainband exits the Catalinas. Nice lighting, though.
6:32 PM. While the rain may have washed a lot of dust out of the air, more dust invaded the area as soon as the rain ended.
6:32 PM. While the rain may have washed a lot of dust out of the air, more dust invaded the area as soon as the rain ended.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

The End, finally.

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.