The “entrance” of our major cold front yesterday was spectacular! Hope you were able to stand upright in the wind, gusts to 60 mph, that just preceded it and saw that arcus cloud march across the Tortolita Mountains and into Oro Valley and Saddlebrooke. If you didn’t, its reprised here, of course.
The arrival of the rain and front was PERFECTLY predicted1 by the U of AZ model night before last; the first drops were supposed to fall between 3 and 4 PM, and by 4 PM, there they were, framed by one of the most spectacular arcus cloud formations I have ever seen. Let’s look now, instead of wading through the whole cloud day leading up to it. Feature a lot of views of the same thing, zoomed differently, it was THAT spectacular:
3:46 PM.3:46 PM.3:46 PM.3:49 PM.3:52 PM.3:58 PM. The engulfing of Saddlebrooke.3:58 PM. And as it passed over Sutherland Heights. Not quite as spectacular appearing as elsewhere.
Here’s what the temperature did yesterday afternoon as this arcus cloud and wind shift line hit:
A temperature record (in Fahrenheit, of course) of our cold front passage yesterday. Got down to 37° F for a few minutes before the recovery started.
The End
——————————– 1CMP got a little overexcited and had rain in the area prematurely in his own forecast (i. e., rain in the area beginning between 11 AM and 2 PM), trying to go 1 up on the model. Bad idea. And no ice whatsoever was seen in those afternoon Cu that started to develop, as CMP was SURE was going to happen, eyeballs straining for ice. Didn’t see the expected precursor lenticulars, either!
Above, a typical Los Angeles Times headline for a southern California storm when the writer was growing up, one framed for Catalina. Few storms don’t do this, so it was always kind of funny.
To coninue on a nostalgic stream for some reason, the LA Times also had a very weather-centric publisher-owner1 in those days, and after a storm, there was also a HUGE rain table in the paper. I loved ’em, scoured those tables to see who got what amounts, and I think a lot of people do like them, so’s that’s why I put a rain table in here from time to time.
Below, the Pima County ALERT gauges 24 h precipitation totals ending at 3:24 AM today, covering the first batch of rain. Scattered light showers, possibly today, but more likely tomorrow, may add some to these totals, but not very much.
The Sutherland Heights portion of Catalina received 0.57 inches.
Gauge ID Name, Location
Catalina Area
1010 0.67 Golder Ranch, Horseshoe Bend Rd in Saddlebrooke
1020 1.02 Oracle RS, approximately 0.5 mi SW of Oracle
1040 0.63 Dodge Tank, Edwin Rd 1.3 mi E of Lago DO Parkway
1050 0.71 Cherry Spring, approximately 1.5 mi W of Char. Gap
1060 1.10 Pig Spring, approximately 1.1 mi NE of Char. Gap
1070 MSG Cargodera Canyon, NE corner of Cat. State Park
1080 0.98 CDO @ Rancho Solano, CDO NE of Saddlebrooke
1100 0.55 CDO @ Golder Rd, CDO at the Golder RD bridge
0.81 inches average
Santa Catalina Mountains
1030 0.87 Oracle Ridge, about 1.5 mi N of Rice Peak
1090 0.51 Mt. Lemmon, snow melt will add to this
1110 1.10 CDO @ Coronado Camp, CDO 0.3 mi S of Coronado
1130 1.30 Samaniego Peak, Samaniego Ridge
1140 1.30 Dan Saddle, Dan Saddle on Oracle Ridge
2150 0.43 White Tail, Catalina Hwy 0.8 mi W of Palisade RS
2280 0.51 Green Mountain, Green Mountain
2290 0.28 Marshall Gulch, Sabino Creek 0.6 mi SSE of Gulch
Your storm day, beginning with a morning light show amid the overcast Stratocumulus:
7:26 AM. Spotlight on the Tortolitas.7:25 AM. Light on Saddlebrooke and environs.7:27 AM. Closeup of the sunny highlight on Saddlebrooke.7:49 AM, toward the C-Gap. Breaks in the overcast (BINOVC, as we would text that) reveal a higher layer of Altocumulus clouds. Nice lighting here, too.8:00 AM. Streams of dark Stratocumulus clouds rolled across the sky for hours yesterday with no rain falling from them. I bet you know why they didn’t rain.9:36 AM. The Stratocu had deepened up enough by this time to begin preciping, and I am sure you made a note of this. The misty nature of this made you also think it might be a “warm rain” process, one not involving ice crystals. However, it did not continue.11:33 AM. Light showers finally began to develop SW of Catalina after a two hour hiatus. Remember how we were thinking that showers might be numerous by now. Well, it didn’t happen. But even these pretty much fizzled out on their way here.12:31 PM. The wind shift line marking the cold front, marked by an arcus cloud (a sharp lowering of cloud bases in the lifting, cooler air), appeared NW-NE of Catalina. Real rain was just ahead.1:55 PM. Eventually the arcus cloud (horizon) and wind shift line made its way across Oro Valley. You can see how that clash of winds has deepened and darkened the clouds over it. Was thinking, “Here we go!”, deep Cumulonimbus clouds would now develop, likely as you did, too. But only weak, puny ones did likely with crappy, mounding tops.2:09 PM. Sure, there was a nice shaft, and was hopeful this would lead to some thunder, but it pooped out even before getting here! Wind shift line seemed to come in two surges, the first one dying out.6:18 PM. Sun tries to perform a colorful sunset, but fails.6:18 PM. Reflected light off orange cloud tops, or a higher layer being underlit by the fading sun, created a mysterious orange glow on the Catalinas and Pusch Ridge.4:50 PM. Some potential for flooding was forecast, and here we see that it indeed verified yesterday.
The weather way ahead
A pretty good rain threat still appears in the March 11-15th window.
The End, except for a gigantic historical footnote below.
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1In 1981, at the prodding of Otis Chandler, the weather-centric owner of the Times, there was EXPANSION of the weather page while the paper devoted an astounding amount of pages to a review weather reporting in the media entitled, “Weather: Everyone’s Number One Story.” One side bar, embedded in this HUGE article took note of the Los Angeles weather situation with the humorous side bar, “Little rain, but lots of coverage.” You can see that article below, scanned from the original clipping from 1981. Its a little disjointed due to the odd sizes of article pages. This article noted that a five month study in 1977 showed that the Los Angeles Times had MORE FRONT PAGE weather stories than any other newspaper in the country!
(Note written on Dec 22nd! Something happened to the title I gave this previously, so its been titled now.)
Didn’t seem possible that such a fast moving storm could drop this much! Neither did the mighty Beowulf Cluster at the U of AZ think so much would fall here. But there it is, a great addition to December’s 1.34 total from the three prior days of rain, pushing our December total to 1.82 inches, just above the December average for Catalina of 1.72 inches (corrected).
Here are the ALERT system gauge reports from around the region at 5 AM AST. You will see that the Bridge at CDO Wash and Lago del Oro got more than here, 0.51 inches, quite unusual, even though its only a half mile a way. Its lower than here.
Don’t be fooled by all those low totals in the Catalina Mountains, that’s because the gauges don’t work when the precip is SNOW! Get your cameras ready for a spectacular, snowy Catalina Mountains scene this morning.
In all of this rainfall data you will see that our half inch is about the MOST recorded anywhere in the lowlands, which can be attributed to the type of storm and the flow it had, more west to southwest flow at cloud levels. That flow caused clouds to thicken up over the west side and up top of Catalina, helping to wring more rain/precip out of them than flow from the south at cloud levels.
In classic fashion, the temperature plummeted about 15 degrees as the front barged through Catalina at 2:30 AM AST, now at 38 F at 4:45 AM. Now (5:12 AM) that the rain has stopped–it will be a gorgeous, if cool day, the temperature is rebounding. Here’s this morning’s temperature trace, pretty dramatic:
The first recording rain gauge bucket tip last night here, indicating an accumulation of 0.01 inches, happening as the rain began to beat against the windows of the house, was at 2:07 AM. The forecast for the onset of rain from this keyboard yesterday was 2:08 AM. I hope nobody got wet due to an errant (semi-facetious) forecast…
Today?
Small Cumulus clouds, that’s it, a gorgeous day with fantastic views of the snow covered Catalinas, punctuated by passing cloud shadows. Doesn’t get any better than this!
Ahead?
More precip before the end of December. Christmas Day now a rain day according to last night’s model run. That run indicated it would be nothing extraordinary. But we reject that notion for the time being, that a storm on or about Christmas Day and later in the month will be more than just a run of the mill rain. This rejection based on our venerable “spag plots” that continue to indicate stronger storms than ordinary during the last week in December and early January. The thought here is that the run of the mill quarter inch or so rain indicated on Christmas Day is an outlier model run. More rain on that day will show up later….we hope! The superior Enviro Can model is make that Christmas Day storm look much more potent, BTW.
Yesterday’s clouds
What a pretty day it was! “Pretty Cirrus” again, then some Altocumulus perlucidus, finally Altostratus translucidus, shown in order below.
10:08 AM. Cirrus uncinus (hooks and tufts at the top) and Cirrus fibratus (gently curved fibers).
The surprise of the late afternoon, and one that strongly indicated that this front would produce more precip than expected, was the sudden obscuration of the peaks of the Catalina Mountains by Stratocumulus clouds around sunset. I couldn’t believe it, and it was a strong sign of a moist current ahead of the front. Still, I could not imagine a half an inch!
4:41 PM. 4:41 PM. The strong indication that last night’s front was going to be more potent as a rain producer; the sudden appearance of mountain-topping Stratocumulus clouds.5:33 PM. Holes in the Altostratus overcast beyond the horizon led to a few underlit rays that underlit the layer, resulting in a bifurcated color arrangement.
Little cell going by (aka, weak Cumulonimbus). I hope you’re up to enjoy the sounds of a good cellular rain on the roof. I feel like another song coming on. Ooops, same one, but its a good one because it not only has rain and thunder in it, but also pathos1. (I thought the thunder in this song gave it a lot of dramatic impact, and we had some thunder NE of Saddlebrooke yesterday afternoon around 2:45 PM.)
Cell has added 0.03 inches to our 0.13 inches and this morning’s total is now a quite nice 0.16 inches on top of the 0.30 we got yesterday. Raining harder now after it let up! Oh, that didn’t last long. Dang.
Total here at 6:55 AM: 0.18 inches! Two day total here, 0.48 inches.
This is so great since this second part of this two part storm was “marginal” as a rain producer, might have only produced 0.05 inches as the bottom estimate for rain, made a few months ago (just kidding), with a top possible amount of 0. 40 inches. So, we’re getting close to the middle of the prediction range made so long ago, 0.225 inches, a prediction you may remember, one that was based on spaghetti.
This rain is associated with the strong cold front that passed through Catalinaland about 2 AM, just after those strong gusts occurred, 30-40 mph last night. Here’s what the nighttime temperature did, drop 14 degrees!
And, as you no doubt know, the atmosphere pressure goes up instantly as the cold front goes by and the colder heavier air piles on top of you. (Time hacks don’t match on these charts for some reason–have not noticed that before….)
Arrow points to passage of cold front at Catalina, AZ.Atmospheric pressure on top of you here in Catalina, AZ. Arrow denotes cold front and rise. With this denser air, you may notice that you’re having difficulty getting up, moving around as you push more “molecules” of air around for any given movement compared with yesterday when the air was not so dense. It also might be because you have more clothes on today…. Hahahaha
Here’s a really nice link to radar happenings locally from The Weather “Underground” (nothing to do, BTW, with “The Weathermen” of the 1960s-70s even though it sounds like it).
Learning module….skip if bored already.
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One of the things that is happening right now at 5:01 AM LST, is that cells are appearing on the radar or intensifying as they move toward Catalina. This happens a lot when the air at cloud height is moving toward the Catalinas and upslope toward Oracle and Mammoth, getting squeezed between the Tortolita Mountains and the Catalinas. That lifting makes the tops go up to higher colder levels, and when the tops to the west and southwest are too warm for ice formation, say above -10 C (14 F), then just a bit of lifting triggers ice formation making a cloud “visible” on radar as the ice grows in size into snowflakes, maybe collides, too, with some itty bitty cloud droplets (too small to be seen by radar) growing even larger and falling faster. This is maybe the biggest reason why Catalina has so much more rain than upwind areas (17 inches annual rain) compared with about 11-12 inches upwind. Most of that difference comes in the wintertime in situations like this, and so some extent, like yesterday’s more general rains.
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What’s ahead for today?
Back edge of this rain band, more or less solid clouds dotted with deeper ones producing rain, is on the doorstep.
Here it is as of 4:45 AM from the U of AZ Weather Department Satellite Facility, with a CONSIDERABLE amount of arrows and writing on it:
So, according to this “diagram” the back edge of this band on the sat image should be here by no later than 10 AM today, that is, chance of additional rain up until around 10 AM in a brief shower, but only a hundredth or two likely. After that, just clouds, probably a lofted Stratocumulus layer, then a widespread clearing with scattered to occasionally broken Cumulus.
Since it is so cold aloft now with the freezing level around 5,500 feet (snow shower now (7:29 AM) on Samaniego Ridge), ice will like form even in modest Cumulus clouds this afternoon, that means virga or maybe an ISOLATED light rain shower possible through around dusk.
Yesterday’s clouds
Here are some of the best cloud photos from yesterday, such a pretty day here in Catalina, where Cumulonimbus clouds stayed just to the north of us off and on all day.
1:19 PM. Cumulus congestus/Cumulonimbus with a young turret on the left that has not yet glaciated (though there is ice inside without doubt) and an older turret that one on the right that is completely ice.2:31 PM. Cumulus mediocris/congestus over the Catalinas.2:44 PM. This Cumulonimbus with a graupel shaft produced one roll of thunder.
5:24 PM, dessert. Some remaining Cu bottoms turn gold in setting sunlight. On the horizon, the frontal cloud band.
The End, at last!
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1Actually, I made it sound like I wrote this song in yesterday’s blog, but in fact, I did not, though I WOULD have if I had thought of it. Note that the person who uploaded this song to You Tube, did not know how to spell, “Cascades.” No wonder we’re falling behind.
Seattle’s Curt Cobain might have said something like this if he had lived in the desert. Alluding, of course, here to the SEATTLE teen angst band, Nirvana, and their big hit, “Smells Like Teen Spirit”. BTW, a song covered later by Bill Nye the Science Guy in an educational ditty, “Smells Like Air Pressure”. But why do this, have a title like this? Contrived, ludicrous “cleverness.” The world needs more honesty.
Began as a good rain at 2:40 AM, and by 4:20 AM, was changing to snow, for those detailed oriented folk. Measured 2 inches on two locations here at 3200 feet, top of the car outside and on the “barbie” cover just as the snow was letting up around 6:30 AM. Two minutes later, it would not have been as deep since all of the surfaces are above freezing in temperature and the snow depth lessens by the minute. This was the third or fourth snowfall here in Catalina since we moved here in mid-2008, and was just that bit more than the “record” deepest of 1.5 inches in December 2008.
Here’s the SHARP FROPA, passage of the dramatic cold front “plus”) this morning at 3 AM as seen in the temperature and pressure records (software is a bit immature and won’t allow printing of two parameters on the same chart). Note sharp rise in pressure at “FROPA”, the classic sign of a cold front’s passage.
La Nina-like conditions seem to return over the next couple of weeks, so lay back and enjoy the soil moisture while you can! Some photos, the first something we Arizonans (of late) called an “Arizona Christmas tree”, a snow covered cholla cactus.
Though HUGELY disappointing because only a trace of rain fell here as of 7 AM this morning, and only a little in the Canada del Oro wash watershed (amounts here), nevertheless, what a nice, classic passage of a cold front. A cold front, as it sounds, marks the advancing boundary of colder air that is displacing warmer air, and that went went by late yesterday afternoon. When it goes by, the wind direction changes almost instantaneously, the temperature begins to drop, often sharply at it did at 5 PM yesterday (see below), and the barometric pressure begins to rise.
But without measurements or satellite or other data, you yourself could have seen that invisible boundary approaching Catalina by the low, scruffy clouds that began to appear on the horizon to the northwest. Soon they were topping the Tortolita mountains, then the Catalinas. And you would have noticed that, unlike the clouds overhead, those lower clouds were advancing from the north. That evolving scene looked like this, finally ending up as a low overcast of Stratus clouds. The first shot below was at 4:40 PM, 20 minutes before the windshift and temperature plummet hit. The second shot is as the windshift was passing Golder Ranch Drive and shows the lower cloud bases associated with the cooler air racing south along the west side of the Catalinas. You can see that they are also connecting to the higher Stratocumulus layer. The third shot shows the Catalinas fully enveloped in the cooler air and lower clouds, and the last shot is of those much lower clouds (I would call them “Stratus”) over Catalina and Oro Valley, looking to the west.
You can also relive yesterday’s clouds and windshift from the vantage point of the University of Arizona’s timelapse film. You will see the windshift hitting there marked by puffs of dust from the NW and then those low scruffy clouds right behing beginning about 5:20 PM here.
So why didn’t it rain with all these clouds? What was missing? For almost every drop of rain that falls in Arizona, ice crystals are required to start the precipitation process going.
The formation of ice in clouds is a continuing scientific enigma, believe it or not. However, we know that they didn’t form, with brief exceptions yesterday afternoon when a few sprinkles (NOT “DRIZZLE”, dammitall! Sorry, lost control there for a second)…..formed in the higher deck of Stratocumulus clouds, and again last evening when it rained again for a few minutes.
The first thing you would guess then, since we are talking about the formation of ice in clouds, is that the tops of the clouds did not get cold enough, that is, were not high enough above us and upwind of us, for ice to form. That would be my best explanation for those periods where it was not raining, we had low clouds and they looked rather threatening for much of the time between 5 PM and dark. (After dark, some rain did briefly fall.)
However, the Tucson sounding launched yesterday afternoon around 4 PM shows that the tops were plenty cold enough; the top of the moist layer was about -20 C! (Note: soundings do not measure “clouds”, but rather humidity, from which we INFER clouds). Normally a considerable amount of ice would be expected in clouds having a top temperature that low. Tiny echoes did occur over and downwind of the Catalinas all around the time of that sounding which means that ice was forming precip here and there in the clouds we saw, and measurable precip was recorded in the CDO watershed.
Sure wish I could have been up there in our former research aircraft to check this out more! But, will have to leave this in a bit of an unsatisfactory way.
My apologies if this got a bit deeper than you really wanted to get into.
Yes, if you’re from Seattle or the west side of the Cascade Mountains of the Pacific Northwest, you are going to feel especially at home today. Its dark, even with the sun up, low ceilings and visibility, steady light rain mixed with snow, temperatures in the mid 30s to low 40s, well, that’s home in January. And, here is that “home” right here in Catalina, AZ, for us to experience again! Cloud type? Nimbostratus, often with an underlay of….Stratocumulus and Stratus fractus clouds to kind of provide that ragged, dark and gloomy, splotchy look.
As you may have experienced this morning, an extremely sharp cold front came through with a spectacular drop in temperature and a windshift at 6:30 A. M. The temperature dropped from the upper 40s down into then upper 30s in only about 20 minutes, which it pretty unusual. Along with the that temperature drop, the rains came in the “frontal band”, now totaling 0.80 inches here since the first period of rain began late yesterday afternoon (local weather station data here). (BTW, this station’s wind data are averaged over 10 min, and gusts are 1 min averages. Multiply gusts by about 1.5 to estimate the velocity of the strongest, few second duration puffs.)
This storm, still in progress, brings the Catalina rainfall for December up to 1.93 inches. Normal, based on a 31 year record provided by the folks at Our Garden here in Catalina, is 1.44 inches. So with this storm, we have exceeded the normal AND crushed the monthly NOAA prediction of well below normal precip this month. Yay! Such predictions are partly derived from the effects of the strong La Nina now in progress-note colder than normal water along the Equator in the eastern and central Pacific. La Ninas normally hedge the climate of the SW toward drought, and so this has been a great December if droughty conditions materialize later in the winter. The December US-wide precip prediction, FYI: (I should acknowledge a bias here: I am overjoyed when droughty forecasts fail but also overjoyed when wet ones verify.)
About real clouds, weather, cloud seeding and science autobio life stories by WMO consolation prize-winning meteorologist, Art Rangno
