A rainy, drizzly Catalina day; 0.69 inches in The Heights

Yesterday’s cold front packed a few more rain “calories” than expected…. Kind of wrecked my play on beer in yesterday’s blog title as a way of making fun of it, you know, “Front light”. See rain amounts below.

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But before that, a heads up: 1) More rain on way next week, at least a 100% chance of measurable rain during the week, and more storms after that (people will be complaining before long);

2) there are some pretty cloud photos at the very bottom in case you’d like to skip over a lotta verbiage; quite dull writing, hand-waving, that kind of thing about what happened yesterday.

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Personal weather station totals as of 2 PM AST yesterday as rain ended. — Personal weather station totals as of 2 PM AST yesterday as rain ended from the Weather Underground map. The green and yellow areas are radar echoes, yellow the stronger ones.

The official totals are pretty amazing, too, considering our best model was predicting something like 0.01 to 0.10 inches here in Catalina just before the rain started¹. Note below the 2.20 inches at Mt. Lemmon. BTW, we’re now just about at our average rainfall total for December here in Catalina of 1.86 inches and we’ve gotten 1.85 inches so far.

Here’s a truncated rain table for our area from the Pima ALERT gauges (its a rolling archive and so you’d better get there early if you want to see the full lineup of totals for yesterday’s storm):

Pima County Regional Flood Control District ALERT System: Precipitation Report

              Precipitation Report for the following time periods ending at: 04:14:00 12/14/14
                       (data updated every 15 minutes)
              Data is preliminary and unedited.
              —- indicates missing data

    Gauge    15         1           3          6            24         Name                        Location
    ID#      minutes    hour        hours      hours        hours
    —-     —-       —-        —-       —-         —-       —————–            ———————
Catalina Area
    1010     0.00       0.00       0.00        0.00         0.51      Golder Ranch                 Horseshoe Bend Rd in Saddlebrooke
    1020     0.00       0.00       0.00        0.00         0.55      Oracle Ranger Stati          approximately 0.5 mi SW of Oracle
    1040     0.00       0.00       0.00        0.00         0.63      Dodge Tank                   Edwin Rd 1.3 mi E of Lago Del Oro Parkway
    1050     0.00       0.00       0.00        0.00         0.55      Cherry Spring                approximately 1.5 mi W of Charouleau Gap
    1060     0.00       0.00       0.00        0.00         0.75      Pig Spring                   approximately 1.1 mi NE of Charouleau Gap
    1070     0.00       0.00       0.00        0.00         0.67      Cargodera Canyon             NE corner of Catalina State Park
    1080     0.00       0.00       0.00        0.00         0.59      CDO @ Rancho Solano          Cañada Del Oro Wash NE of Saddlebrooke
    1100     0.00       0.00       0.00        0.00         0.43      CDO @ Golder Rd              Cañada Del Oro Wash at Golder Ranch Rd

Santa Catalina Mountains
    1030     0.00       0.00       0.00        0.00         0.47      Oracle Ridge                 Oracle Ridge, approximately 1.5 mi N of Rice Peak
    1090     0.00       0.00       0.00        0.00         2.20      Mt. Lemmon                   Mount Lemmon
    1110     0.00       0.00       0.00        0.00         0.55      CDO @ Coronado Camp          Cañada Del Oro Wash 0.3 mi S of Coronado Camp
    1130     0.00       0.00       0.00        0.00         0.79      Samaniego Peak               Samaniego Peak on Samaniego Ridge
    1140     0.00       0.00       0.00        0.00         0.71      Dan Saddle                   Dan Saddle on Oracle Ridge
    2150     0.00       0.00       0.00        0.00         1.34      White Tail                   Catalina Hwy 0.8 mi W of Palisade Ranger Station
    2280     0.00       0.00       0.00        0.00         0.59      Green Mountain               Green Mountain
    2290     0.00       0.00       0.00        0.00         0.98      Marshall Gulch               Sabino Creek 0.6 mi SSE of Marshall Gulch

Hell, there wasn’t any rain in the cloud band west of us when I got up, and so I thought with some lifting, and that jet core at 500 mb slipping southward from southern Cal as the day went on, rain would develop farther south in the frontal cloud band. It did, of course, but still thought it would blow through in 2 h or so, something akin to the models as well. The rain fell for about 5 and half hours! The clearing took place a little before sunset, not in the early afternoon as expected.

So what happened?

I think you and I overlooked a disturbance aloft behind the frontal band. It was sliding SEwd fast from Nevada, catching up to our little frontal band. When those things happen, clouds magically seem to be appearing on the backside of the frontal band, fattening it up, holding its progress back; and the rain areas get bigger. The frontal band was MUCH fatter when it went by TUS than it had been just a 100 or so miles to the west at 4 AM AST yesterday morning. Here are contrasting satellite and radar images for two periods yesterday, before the band fattened up and the second, when it was raining so much here:

Satellite and radar imagery for 4:30 AM yesterday. Sneaky backside disturbance is represented by those clouds near Vegas. No rain echoes west of Catalina, stop along the Pima County line making it look like rain will be marginal here.

BY 1:30 PM in this satellite image with radar, the band is twice as wide and there's rain all the way down to Mexico way. — BY 1:30 PM in this satellite image with radar, the band is twice as wide and there’s rain almost all the way down to Mexico way. Look how those clouds and showers near Vegas have caught up with our front, almost attaching themselves to it in north central Arizona. Lots of times this process of upper air disturbances catching up to a front generates a cyclone along the front as the front widens and begins to kink. I think that’s what happened anyway. Whatever. It was a great confluence of events for us here in Catalina. Think how the wildflower seeds are feeling right now with already an average amount of rain for December, and its not half over, and more is on the way, yay!

If you’re a true C-M disciple you noticed something else yesterday: true DRIZZLE in the rain. Drizzle may be even more rare than snow here. And the thick low visibility rain consisting of smallish drops from drizzle sizes, 200-500 microns (a couple to a few human hairs in diameter) and raindrops just above those sizes for much of the time the rain fell, should have made you start thinking of a warm rain process day. Maybe there was no bright band in the radar imagery during those times, something that happens when rain is ONLY formed by colliding drops that get big enough to fall out; no ice nowhere. In the heavier rains, sometimes when visibility was improved, ice was very likely involved.

The TUS sounding really can’t shed light on this question since the morning was had shallow clouds that weren’t raining yet, tops barely below freezing, and the 5 PM AST sounding, with tops at -10 C (14 F), was a little too late, though that layer that was sampled did produce what appeared to be ice virga in the direction of TUS about the time of the sounding. BTW, its well known that “warm” rain processes that don’t involve ice occur at temperatures below freezing, so the expression is a bit of an oxymoron.

So, without radar imagery over us during the time of the thick rain and drizzle, we can’t say for sure, but it sure looked like it to C-M, which is what you should think as well I think. Thanks in advance for thinking what I think.

Enough of my excuses², let’s rock and roll with yesterday’s clouds

Your cloud day

7:35 AM. Light rain, looking suspiciously like "warm" rain, spreads over the Catalinas. Its only gonna get better from here and frontal band barrels in on Catalina. — 7:35 AM. Light rain, looking suspiciously like “warm” rain, clouds not looking so deep, spreads over the Catalinas. Its only gonna get better from here as frontal band leading edge is just across the street over there on the Tortolitas.

8:09 AM. "Oh, what a crummy front, things breaking up already", you were thinking. Also, "Look at how shallow those clouds are! Terrible." Sometimes these brief thin spots or clearings are called, "sucker holes." — 8:09 AM. “Oh, what a crummy front, things breaking up already”, you were thinking. Also, “Look at how shallow those clouds are! Terrible.” Sometimes these brief thin spots or clearings are called, “sucker holes.” Hope you didn’t fall for it like I did. (Just kidding.)

9:43 AM. R--F (text for "very light rain and fog"), rain has piled up to 0.10 inches. But you notice there's something different about the rain, its thicker, smaller drops, even drizzle drops in it. You begin ask, "Could this be a solely warm rain event?" I think so. — 9:43 AM. W0X1/2 R–F (text for “indefinite ceiling, zero, sky obscured, visibility 1/2 statute mile in very light rain and fog”), rain has piled up to 0.10 inches by this time. But you notice there’s something different about the rain; , its thicker, small thick drops hardly making a splash in puddles, even drizzle drops in it. You begin ask, “Could this be a solely warm rain event?” I think so. Note disappearing telephone poles.

12:46 PM. After several hours of rain, flood waters begin to appear. Note mottled surface of this lake, showing that the drops were making good splashes at this time. Rain intensity deemed R (moderate) then. — 12:46 PM. After several hours of rain, flood waters begin to appear. Note mottled surface of this small rain-formed lake, showing that the drops were making good splashes at this time. Rain intensity deemed R (moderate) then. Deemed not a warm process rain at this time due to those drop sizes and less bunching, fewer small drops in between the larger ones, visibility was about 2 miles in rain.

The best scenes of all were when the clouds began to part in the late afternoon and evening sun. I hope you caught these beautiful scenes:

The End

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¹Total rain prediction from our best model, the one from the U of AZ with the predicted totals through 3 PM AST yesterday. The model run was at 11 PM AST the evening just before the rain began:

Ann RaIN THROUGH 3 PM 12-13 — The arrow points to our location, in which only a tiny amount of rain was predicted. Mod doesn’t miss very often by this much, but the earlier December storm had the same mod problem, too little in the model compared to what actually fell here. Gee, new thought… Could it be a poor representation of the warm rain process? Hmmmm.

²Your Catalina C-M did have a correct range of amounts that could fall in yesterday’s storm right up until the last minute. For weeks he was predicting, and staying firm with, 0.15 inches on the bottom, and a voluptuous, if that’s the right word, 0.80 inches potential on the top.

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.

View all of Art Rangno's posts.