Rain totals and some cloud shots and a bright rainbow

Pima County has a rolling archive of 24 h rainfall.  Below under “Table” are those totals as of yesterday, at 4 PM AST, probably that 24 h period capturing the full storm.  Here in Catalina, with another 0.21 inches after 5 AM, our 24 h total ended up at 0.96 inches; 0.98 inches at Sutherland Heights, 1 mi NE of this site.  The most in our immediate region is 1.57 inches at Pig Spring just NE of Charoleau Gap.   We seemed to have captured the most that this situation could have produced. ‘Bout time!

ALERT network Rain Table, 4 PM the 13th to 4 PM the 14th. Click “Table” to see.

After the steady rains of early yesterday the sky broke up into one reminiscent of a summer day with those cold Cumulonimbus clouds and dense rainshafts, and some spectacular rainbows. But some of our greatest beauty is when the sky breaks open and the clouds and shadows quilt the snow-capped Catalinas.

4:35 PM looking SE on the Catalinas and Pusch Ridge. An icy, pretty well glaciated Cumulonimbus cloud drops another inch or so of snow.
4:34 PM. Simultaneously, another cold Cumulonimbus cloud and its last bit of trailing rain produced this luminary. Typically brighter rainbows occur when the raindrops are larger. The bow ends at the top because its snow, not drops.  Its a nice graphic of where the snow level is.
2:28 PM. Stratocumulus top the Catalinas and water-covered rocks glisten in the the brief sunlight (look above road).
Also at 2:28 PM, farther north along the snow-capped Catalinas.  So pretty.


















1 PM. Example of the summer-like appearance of our cold Cumulonimbus clouds yesterday, this one over the city of Tucson.
3:08 PM. Another summer like scene showing a “Cb” moving into the Oro Valley.









What’s ahead?

Today:  Its raining now at 5:15 AM, what we would code as “RW–“, two minuses indicating “very light rainshower”, not measurable unless it continues for many minutes. (It didn’t.)  Some might have called it a sprinkle, but if you’re really weatherwise, you would NEVER call it “drizzle”!  C-MP (the writer) gets overly worked up when people call sprinkles, “drizzle.”

——small harangue—–

Drizzle, to repeat for the N+1 timeth, is composed of fine drops (less than 500 microns in diameter) that are close together and practically float in the air.  Umbrellas are much good in even the slightest wind; forget about it seeing well if you wear glasses and your riding a bike with a baseball cap.  A baseball cap can work pretty well in keeping your glasses free of drops in REGULAR rain composed of drops larger than 500 microns in diameter, mostly millimeter sizes, ones that fall rapidly, and don’t have time to get under your baseball cap unless its REALLY windy, or your going awfully fast.

—–end of small harangue—-

Now, where was I?

Oh, yeah…  We’ll have passing light showers today, maybe a few hundredths to a tenth of an inch is about all we’ll be able to manage today; if everything was perfect, a quarter of an inch. Better check the U of A model….see if it agrees.   Oops, not done yet, or is busted.  Oh, well.  We’ll continue to be north of the main 500 millibar current (see below), a necessary but not sufficient factor for rain here in the wintertime.  Means the clouds will be cold and ice likely to form in them as the day goes on and what sun we have deepens them up a bit, as well as an enhancement as our weak, incoming trough goes by during the day.  Anything is welcome!

Here’s the mid-day pattern aloft, from IPS MeteoStar:

Way out ahead

Its always exciting when you’re in a trough bowl, the location where the average position of one of the four or five waves (troughs) around the globe are.  When you are in one of them,  as we are, they function like storm magnets for your location.  Individual storms head in your direction, usually from the west or northwest, “bottom” out in latitude, then “eject” out to the northeast.  Our wettest SPELLS are characterized by the positioning of the average or “mean” trough in our location (“trough bowl” its been called here).  Doesn’t mean that it rains everyday, but there always a new storm heading in your direction until the pattern changes and the “mean” trough moves somewhere else.

So, we got another rain chance on Wednesday, looks similar to this one, probably light, but then later, the models are suggesting a chance for more substantial rains associated with some very strong troughs that move in within the 10-15 day range, or from December  24-30th.  Check out the size of this big boy on the morning of December 25th at 5 AM AST compared to what is passing over us today.  Note how much farther off Baja the main, broad band of the jet stream is flow.

Valid, 5 PM AST, Christmas Eve. Look at the clustering of red lines in northern Mexico in this cropped version. This jndicates that the forecast of an upper trough in this area at that time is VERY likely, not certain, but I’d out money on it.

I wouldn’t bother getting you excited about something this far out unless there was some good support in the spaghetti. Below is a cropped version of that plot (the full one below), concentrating on our area.

Remember what Edward N. Lorenz, an MIT meteorologist asked in the title of a paper when he developed the chaos theory:  “Predictability: Does the flap of a butterfly’s wings in Brazil set off a tornado in Texas?” (Thanks to the AZ Star for publishing this quote recently.)

So, in doing these “ensembles”, that is, running the computer models over and over again with slight errors deliberately introduced to produce these differing sets of lines in our “spaghetti plots, we are trying to see how different a forecast will turn out, with, figuratively, “butterfly wings” flapping around that we don’t know about.

If the lines don’t change at all from the original model run using the data that came in, then the forecast will be realized as it was first presented.  If the lines look like a bowl of rubber bands (as they are below in the full plot for Christmas Eve), then the forecast is unreliable, subject to huge changes in time.  But, those red lines south of Arizona are well clustered, indicating, figurotively speaking, that no “butterfly” is going to change it.  So, troughs predicted in the actual run for that time period, are almost certainly going to verify.

In sum, watch for a stormy period around Christmas.

Finally, the end, I think.