The weather ahead – Page 18

Umbrella, galoshes, windbreaker at the ready

Low forming in AZ. Jet stream (at 500 millibars) goes by/strengthens to the SE during day; therefore, expect rain to begin before 5 PM, but not before 11 AM. It should continue off and on for about 24 h afterwards (in case you don’t watch TEEVEE where YOUR weatherman/gal will be telling you much of what is below. But to make it that much more interesting for you, this: (Cloud pics way at bottom in case you want to skip all this.)

Let’s play, “Beat the Model!”

Kind of a “fun” day for us amateur and highly paid media forecasters since rain will develop where there is none upstream of us; clouds will thicken downward from the Cirrostratus/Altostratus with Altocumulus as the day progresses, with light rain beginning from that process, heavy layer clouds with virga that eventually reaches the ground as the atmosphere moistens up. For example, at this hour (4:50 AM AST) there are NO radar echoes from precip in all of Arizona, somewhat surprisingly.

As part of the “game”, and AFTER laying this out this rain onset timing (rain beginning after 11 AM and before 5 PM in Catalina, that is, best guess, first drops in mid-afternoon), its then fun to see what the very latest super Beowulf Cluster model of the U of AZ says, the best of the best. Its a test of how well you and me are “learning the territory”; “don’t need no model” if you truly understand our SE AZ patterns (when rain occurs relative to air flows aloft like jet streams), know the local and upwind terrain effects because you’ve lived here long enough, can read satellite imagery, etc.

Of course, you can’t really do this except when the weather is at hand. The models are just too good when it comes to beyond a day or so.

Rain amounts?

Here’s how to make an educated guess from “patterns and such”:

First, determine the outliers, those least and greatest amounts “possible”: bottom of precip amount (if things really go bad) here now looks like 0.20 inches (estimated 10% chance of less), top amount (if things really go well) up to 0.80 inches, (estimated only 10% chance of more than that, i. e., everything appears to be falling into place for a substantial desert rain here. The best guess, now that you’ve figured out the top and bottom amounts in kind of a mental “ensemble”, the average of those two outlier forecasts, 0.50 inches by mid-day tomorrow. That’s it.

Since I have busybeelabored these weather points for some time now for the two of you that read this blog, we should all be making the same interpretations today sans model outputs; just eyeballing stuff, doing our own thing, getting a handle on this storm by really THINKING about it, not just soaking in some model output quite yet. Don’t peak yet! This is better than Sudoku, Angry Birds, bajan, facebook, etc.

NOW let’s peak at the U of AZ model from 11 PM AST to get the latest, best prediction for Catalina and see how it matches up with our own forecast based on perusal of a few simple model charts, sat imagery, dewpoints, etc.

Here are the U of AZ Beowulf Cluster outputs, run from 11 PM AST data. The rain arrival in Catalina is shown in the panel below and its between 5 and 6 PM AST, moved up from 10 PM on the run 24 h ago, but a few hours later than our SOP (Seat of the Pants) forecast above.

This is so great! I love this competition! Its weather sports! Its great to tweak the model’s nose, the model with its billions of calculations when maybe you’re own grades in calculus weren’t so great! I am pumped about rain before 5-6 PM!

Now for a comparison of our amounts….

Beowulf predicted amount: between 0.10 and 0.50 inches from this map below by noon tomorrow (when most of it should be over), which shows the heavier rains to the SE of us, ones up to 0.7 inches.

These Beowulf model amounts are often on the HIGH side, and so this is of some concern for us and our prediction, since this model foretells a tenth to a quarter inch or so by 1 PM AST tomorrow when the precip is over except for spotty light passing showers. If that is an amount pushed to the high side, egad!

So, we’re (I’ve roped you into this) a bit on the high side of a model prediction that is known to push rainfall amounts already toward higher than observed. Hmmmmm.

Those lower predicted amounts in the model are probably due to all the low dewpoints we have to overcome with a nice Gulf of Cal/subtorpical influx, and that influx, the model thinks, will end up arriving to the southeast of us. Uh oh. Too late to back off rain amount guess, will ride out the storm; Riders of the Storm Amount, you might say to break up the boredom here a bit.

Now, if you were going on TEEVEE with a forecast after all this investigating, you might, after your educated guess, tweak our own forecast some; somewhere between the original one, which was pretty original, and these model ones. Works out for the best that way. We used to call this, the “man-machine mix”. We still do it.

What can we learn from this exercise?

If those green areas (those having more than 0.50 inches) are farther to the west and over us, we might be detecting a slight eastward bias in the model in these kinds of situations when the moisture roars out of the south-southwest as it will today. No doubt about it, we will be on the edge of the major rains! Fingers crosssed.

I have to admit that due to an internal pro rain bias, I am often on the high side of rain amount predicting.

Wouldn’t it be great if newspaper stories about political events had bylines like, Joe Blow, Democrat, “disclosures” so we might read between the lines some, etc?

Yesterday’s clouds

In a word, phenomenal. So many gorgeous patterns up there in those Cirrus and Cirrocumulus clouds yesterday afternoon, I could hardly take enough photos of them. Like etched glass, this beauty:

SONY DSC — 3:40 PM. Cirrocumulus transitioning to Cirrus (left to right). Cirrocumulus are nearly always droplet clouds. Here, at an estimated -32 C from the TUS sounding, and at 22,000 feet above Catalina, those droplet specs of Cirrocumulus clouds quickly froze, and as ice crystals in them grew they began to trail gently downward. If you were up there in an aircraft, flying those those ice crystals, you would see something akin to tiny sparkles of light, like diamonds glinting in the sun. When the wind decreases in velocity and changes direction some below the parent cloud, you’ll get these beautiful, delicate strands (as at right), each strand representing the remains of one of the droplet cloud specs that froze. So pretty!

I think you should see this….

http://www.atmo.arizona.edu/products/models/wrf_d01_0/wrf_precip_tot.html

and this:

http://www.atmo.arizona.edu/products/models/wrf_d02_0/wrf_precip_tot.html

from our venerable U of AZ Department of Atmospheric Meteorology. They’re both quite good outputs with substantial Catalina rains in them.

Yep, MEASURABLE rain is in the bag! Virtually certain!

Amounts? Mod examined above says we’re in the 0.25 to 0.50 inches, with more, of course, on Ms. Mt. Lemmon and Cat Mountains. Begins tomorrow evening after dark. Watch out for a slightly earlier onset of rain here than the 10 PM AST in the second model, IMO.

Should have some nice looking Cirrus today, and maybe a couple of Altocumulus flakes, too. Don’t forget to log them in your weather diary.

Out of town relatives here today, so quitting before blabbing too much. “Yay”, you say…

The End.

Flatlined

The recording raingauge, that is. A coupla drops is all that fell here in Catalina after some indications of cores around us later yesterday afternoon that were producing measurable rain. You can go to the U of AZ rainlog site to see some local amounts–the Pima County ALERT site is down right now. They’ll have some reports in the mountains and elsewhere, providing it wasn’t snow. The most I’ve seen so far is 0.05 inches, lucky dogs.

Some nice cloud sights on a day of dramatic, icy development. I wonder if you say the first Cumulus/Stratocumulus blob glaciating far to the WSW, beyond Twin Peaks? I thought it would happen first toward the NW-N because the air got colder if you headed in those directions. Yesterday’s cloud highlights, once again pioneering here the “novella-sized”, explanatory caption:

: 3:58 PM. By this time it looked very promising for a few hundredths of rain.

The weather ahead: measurable rain!?

I am sure, that due to our fine array of weather practitioners on TEEVEE (ones that make an incredible amount of money, mind-boggling really, and ones that have the same kind of fun doing weather forecasting as I do) that rain is in the offing for Catalina in the days ahead. So why bludgeon the topic here? Well, let’s guess a range of amounts that could occur, bottom and top, based on SOP-eyeball of weather patterns and goofy, variable progs:

Last night’s Canadian run, has a near miss now, rain partitioned to the SE of us. Booo! But, then rain with a follow up system on Jan. 1st, maybe with some snow in it here. So between the first threat and the second, both happening between the evening of December 30th and the evening of the 1st, the range has to be wild, maybe not useful. At the bottom, we could be completely bypassed in measurable rain from two strong troughs (we’re still in a “trough bowl” BTW), but I guess if you’re in a drought, you only get misses. But, being the optimist, AND with our own USA! model indicating measurable rain as of last night’s run, the range of amounts over the four days of chances, has to be from a trace to 0.50 inches at most. So, a range with all the factors at play is not too useful.

The average of those two, 0.25 inches, often works out as the closest estimate. Let’s see what the U of AZ has this morning… Oops, no update, budget cuts strike some more!

The End.

Jet stream passes overhead today and tonight, drifts to south; Cumulus and Stratocumulus clouds deepen upward during day and by afternoon tops reach the glaciation level (below -10 C, 14 F) and begin spewing snow virga which melts to rain at lower elevations.

I guess I don’t need to blog after that title… We’ll be lucky to get 0.15 inches, and a few hundredths is the most likely amount, and that will fall later in the afternoon to late evening hours according to me and my (U of A Weather Department) model.

How much the U of A model thinks will fall regionally is seen for this event are seen in the panel below ending at 7 AM AST tomorrow morning, but first a caveat: I just saw this run for the first time now, and did not at first notice that it was OLD, from the night before last, not based on data from last night at 11 PM AST as usual. This lack of a model run might well be due to the effect of budget cuts noted on the link above… Dammitall, budget cuts!

Anyway, check the times of the run to make sure you’re not looking at something old today. I used it anyway because things have been well predicted in our incoming trough and jet stream for a couple of days now.

You can also see that with the jet over and just to the south of us later today through tomorrow morning, that most of the precip is to the north of the jet, as per usual in the interior of the SW¹.

Here’s what the jet stream does in the next 18 h, starting with the forecast for 5 AM AST (these are from the latest data!). The winds are very strong over us now, but a core of strong winds is dropping down from California toward southern Arizona and reaches us later today and then drifts south. As that happens, the air aloft is really cooling off. The temperature at 18,000 feet (500 millibars) drops almost 10 F between 5 AM this morning and 11 AM!

As that happens, the air will be getting more moist from the bottom up. Small Cumulus will form later this morning and their tops will be rising and getting colder by the minute, eventually reaching our ice-forming temperatures around here of -10 C to -12 C, but tops to -20 C are likely late in the day. When ice begins form in these “supercooled” clouds, those crystals grow at the expense of the liquid droplets and fall out.

This cloud drama, if you will, is what makes today extremely exciting; watching for that first ice to form in these lower, relatively shallow clouds. They can be shallow and still develop ice because its so damn cold aloft later this morning and this afternoon.

So, a pretty if cold day, with lots of virga around later this afternoon, and with that, a great sunset is likely, too.

Yesterday’s clouds

More rain in our future after later today and tonight?

Oh, yeah, baby. Its in the bag. A “virtual” certainty (which actually means its not absolutely certain at all, but that’s because its a weather forecast based on imperfect models and humans. Remember that great metaphor about why there’s an eraser at the top of a pencil? Profound.)

OK, when? Let’s start by looking to Canada for rain in Arizona: Here’s a panel from Enviro Can for Monday morning, December 31st at 5 AM AST. Its got rain in it, rain that would have fallen in the prior 12 h leading up to 5 AM. I like this model because it has more SE AZ rain in it than the US ones….

201212312 00_054_G1_north@america@zoomout_I_4PAN_CLASSIC@012_108 — See lower right hand panel for rain in Arizona by the morning of the 31st.

There is a fly in the oinkment. The US models have a big “anti-cyclonic” bulge in the flow over us as our the trough/low approaches us on the 30-31st. These bulges in flow, toward the inner portion of the jet stream, can have devastating effects on clouds and precip formation. A bulge like that is like a high in a low; the effect is to weaken all the upward motions in the atmosphere. The Canadian model has less of that; hence, shows more rain here.

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¹Of course, if you have a copy Willis and Rangno (1971), “Final Report to the Bureau of Reclamation, 1970-71 Season, Colorado River Basin Pilot Project, Season 1”) you already know that.

Rejected! (that 06 Z mod run from last night with no rain here for 15 days)

I had to laugh when I saw the very latest WRF-GFS model run, the run from last night’s 11 PM AST (06 Zulu) that had not ONE green pixel of rain over Catalina in the next 15 days! You can see that really bad run here, from IPS MeteoStar. You’ll get quite a guffaw out of it, as I did. Quite bogus, really, or, as Wallace Shawn’s character repeats several times in the movie classic, “Princess Bride”, “Its inconceivable.” (Of course, he was wrong, but we’ll ignore that.)

Completely dry cannot happen here over this 15-day period, period.

I was really afraid you had looked at this model run right off the bat this morning and had gotten down because of it, so I thought I’d better take it on right from the get go to get you going; so you wouldn’t be sad at work thinking about it all day.

What would be the reasons for firmly rejecting this latest model run, as a defender might a potential layup in a basketball game, this model run send up, the result of billions of calculations on our best, fastest computers? They’d better be pretty good ones, we know.

1. Its based on data at 06 Z when there are not so many observations, lots of gaps in the data, filled in by what the prior model run thought would be in those gaps (possible “fantasy” weather in those).

2. Wildly different from the model run just 6 h earlier (00 Z) 5 PM AST, one that was based on oodles of global data.

3. Is inconsistent with a steady depiction of several rains here over the next two weeks in prior model runs. The big storms during the last week of December into early January, written about here for some days now, are only close calls for us in this latest 06 Z run.

4. It doesn’t agree with the superior Environment Canada model run, either, on the first of these coming rains. For example, the Enviro Can mod has rain here late on Christmas Eve into Christmas Day, as it has steadily of late, while the 06 Z run has zip.

5. Principal reason designate last night’s 11 PM (06 Z) run as a “laugher”, an “outlier”, completely bogus piece of computer trash?

The NOAA-NCEP (National Centers for Environmental Prediction) “Ensembles of Spaghetti“, which we often discuss here. Let’s look at one of these, one valid for 5 PM AST, December 28th. Looks like rain here to me.

Here’s where both nascent CMJs (cloud-maven juniors) can really shine because they know about “spaghetti” and when to reject “outlier” model runs. And they can also impress others with their black, really great-looking, “I ‘heart’ spaghetti” tee-shirts with the colorful example on the front. Shows your in with the “in” weather crowd, always a great thing.

Note the positions of all the red lines (570 decameter heights of the 500 millybar surface) in the above example. They bulge down toward the equator magnificently in the eastern Pacific and to the south of the SW. These red lines virtually guarantee a big trough in the lower (southern) portions of the jet stream on this day and the days around it.

While ordinary folk, and maybe some of the weather practitioners on TEEVEE making huge amounts of money might be chagrined, taken aback by that latest, 06 Z model run and back off big claims and dreams of strong storms ahead, the CMJ will stand tall against this model run and continue to proclaim significant rains in the last week of December into January, ones that will juice up our water year precip totals significantly.

Well, at least I will.

One final note…. The exact day of the major storms in late December are unknown; those will wobble around until the smaller elements/waves in the global picture come more into focus over the coming days. Significant rains might occur on the 28th-29th of December and/or the 30th and 31st, with still another possibility in early January (a bit more dicey, of course.)

In the meantime, before Christmas, a glorious Arizona winter storm break.

The End.

Catalina gets 0.48 inches in brief frontal passage

(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.

More precip totals can be seen via the U of AZ rainlog network here, and statewide totals here from the USGS. The NWS will have some regional totals after 8-9 AM AST as well.

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.

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!

Speaking of storms…the one tonight

Very exciting day ahead as the south to southwest winds pick up this afternoon to gusty proportions with some dust-haze in the air. Cold front coming, as you you know. Surface low pressure center passes to the north. Very exciting, to repeat for emphasis.

Rain? Oh, yeah. This time ALL of it After Midnight (different “reminder” version of this song of when-the-rain-will-start than the one I used last time; different comments, too, on YouTube by people who drink beer late into the night instead waiting for rain… In fact, not one person mentions that he/she was up waiting for rain to start “after midnight”, as you and me might do today.

How much rain here in Catalina this time?

Well, let’s start out by guessing…from weather maps, pattern recognition, and stuff like that. Oh, bottom (estimated 10% chance of less than this): 0.10 inches (namely, it shouldn’t be a dud with no rain at all).

Top amount potential, if everything goes well (only 10% chance of more): 0.40 inches. It doesn’t have the potential of the last blunderbuss of a storm (day 1 of that one where the top of 1.00 inches was realized), but “hey”, its a nice rain in the desert again, helping to plump up those just-ahead spring flowers and grasses.

Best estimate, most likely amount: the average of those two guesses, 0.25 inches¹.

OK, now I have JUST looked at the “B-Cluster” output from the U of A 06 z (11 PM AST) model run for OBJECTIVE guidance, not SOP stuff as above: Rain begins here in this model at 1 AM AST (probably too soon by a couple of hours), and the total amount, as predicted by a computer that might have cost billions? Pretty much the same as me, 0.10 to 0.25 inches! I must be wrong! (hahahahaha).

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Serious note: the U of A could really use a donation from you to help keep stuff like the Beowulf computer cluster going; I’ve contributed. See online U of A Department notice in RED letters, calling out a dire situation here. It would be a shame if some of their stuff goes away.

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Now if you’re a pattern person, you will be noticing that this trough is the type in which Catalina amounts are significantly greater than those to the south, such as in Tucson and the surrounding lowlands, and often this comes toward the end of the storm when we see the rain hanging on for an extra hour or two and the clouds pile up against the Catalina Mountains on our side of them as the wind turns more perpendicular to them as the trough goes by. Always a nice time to look at radar because you see little echoes popping out of a no-echo but cloud filled sky, ones that then head toward us. Here where that trough is at 5 AM AST tomorrow morning, its apex right over you and me!

Note above, in timing the onset of the rain, that by 5 AM AST, the strongest winds of this trough (at this level, 500 millybars) has gone by–forecast the rain to have begun by this time; nice rain beginning time window, with the Beowulf being a bit fast (as per usual): Between 2 AM and 5 AM AST tomorrow morning. Set alarm clock. This is so much fun! For extra razzle dazzle for your neighbors, tell them the rain will start between 2:08 AM and 4:32 AM. You can’t get this kind of forecasting precision elsewhere! This is so much fun!!!

As you know, too, the temperature will PLUMMET during the frontal rainband early tomorrow morning as it always does, maybe 10 degrees F or more in an hour, along with the familiar pressure check (sudden rising pressure, one that occurs just about the instant the wind at the ground shifts from wind from the southwest to northwest zephyrs (sounds like a soccer team).

Yesterday’s clouds

There weren’t any. Hahahahahaha. From the 16th, a picture of a “frosty Lemmon.” (Its amazing how you can just be sitting here, and after one or two cups of coffee, this kind humorous creativity just bubbles up from below. The brain is really something, as the special issue of Science mag will tell you, talkin’ about the hippocampus and neocortex and the mysterious things they do, like thinking that “frosty Lemmon” is funny. You really should read this whole issue to find out what’s going on up there in that cranial cavity you have.)

————Footnote in middle of blog for a deliberate change in normal protocol—————

¹Kind of like footnoting, makes me feel like a real author or librarian… I came up with this technique in Durango, Colorado, in the early 1970s with the Colorado River Basin Pilot Project, a gigantic randomized cloud seeding experiment covering much of the San Juan Moutains. Its based on the fact that we meteorologists often have a better idea, a more concrete one, of what’s NOT going to happen. By estimating the extremes of a storm (the crude weather models of that day off this way or that some), it turned out that you could engineer in a way, a better forecast of the amount that would actually occur. In a sense, doing that was performing a “mental ensemble” or mental spaghetti plot have two members (outputs)¹(kind of like footnoting…).

Of course, in Durango, CO, we had an objective forecast scheme based on the work of the late Dr. J. Owen Rhea, former chief project forecaster in Durango, who came up with the basic idea behind what is now called the PRISM method of estimating rainfall between gages in complex terrain. Used today to present statewide rainfall averages such as this one for Arizona, courtesy of the Western Region Climate Center. This is a very nice guide if you’re unhappy about the rain/snow you’re getting and want to live where there’s more, a true precipophile:

Those big storms just ahead

They’re definitely in the pipeline…. (Here you can feel the confidence slacking that bit from “count on it” yesterday to “definitely” today. Was chagrined by model outputs during the day yesterday, that, while having many AZ rains, were ones having reduced amounts, and were less numerous.

Still, will ride the “Big Storms Wave” right into oblivion if necessary because that’s what I saw in the “ensembles of spaghetti” and they have NOT let me down once that I know of (another fudge phrase).

BTW, what happens after you have seen those wavey lines in the “ensemble members” (each line is called a “member”) is that you come to expect a disappointing output or two–but you don’t really worry TOO MUCH about them, because the Big Boys will be back if the ensembles are correct, as well as your interpretation of them.

So while yesterday during the day the outputs backed off so much rain here as foretold at this very blog, during the night, with the 00 Z (5 PM AST run) not too surprisingly those big rains came back.

In sum, watch for strong storms and big rains in the last week of December into early January.

“Plenty more where that came from”

The models are showing a lot of rain ahead over the next two weeks–see farther down. In the meantime, this:

6:44 AM: back side of last rain blob passing over Catalina now. That should be it for today and the next several days.

It was STILL raining when I got up at 3:40 AM, another few minutes of rain in a never-ending series of brief light rains over the past 24 h. The total now over the past 72 h is no less than 1.34 inches here in Catalina! Wow.

And yesterday, with its persistent overcast, dark, dull, spritzed-with-mist periods of rain (approaching the official “drizzle” precipitation category), was, with its high temperature of only 53 F, as close to am early spring day in Seattle in Catalina as you could experience.

Here are some shots of that overcast with Stratocumulus day with exceptionally long captions as well, a style I seem to have “pioneered”:

And this last rain episode, not even lasting 10 min, has plumped up the rain total for the past 24 h to 0.39 inches here in Catalina at 6:45 AM, ABOVE that amount that it was deemed there was only a ten percent chance of exceeding, 0.25 inches when writing yesterday. So even as much of a precipophile as I am, I could NEVER have foreseen so much here as in the past 24 h!

So, this morning, I am humbled, but feeling great that so much more rain fell in our droughty nearby desert.

Two sites in the Catalinas have received another 0.87 inches as of 5 AM AST, 0.75 inches in the past 6 h! View 24 h totals here, though being a rolling archive, unless you go right away you’ll see slightly different totals than I mention here.

This last 24 h of our rainy spell, too, is a good example of how Catalinans get more rain than in town WHEN the flow turns from almost due south as it was on Friday, to more from the southwest and west as has been the case yesterday and continuing into this morning. When the flow is more westerly, air piles up against the Catalinas AND over us deepening the clouds, ones that begin thickening well upwind, say around I-10 to the west, and then they often start preciping soon after they thicken up as the tops of the clouds get colder and reach the ice-forming level. When the flow is from due south, we are “shadowed” by Pusch Ridge and other portions of the Catalinas to the S, and our rain can be less than Tucson and the north metro area next to the Cat Mountains.

Most of our rain advantage over Tucson (17 inches vs. 12 inches) comes from the kind of days we had yesterday and early today.

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What can we learn from these past 72 hours?

When you’re in a “trough bowl”, as we are now , good things happen; storms often turn out to be better than you imagine, being all they can be, no duds.

“Nice” days now will only be temporary breaks while we’re in the trough bowl, the collecting zone for storms. As an exciting example of how the weather is in a trough bowl, there were TEN model output panels from last night’s run showing rain for SE AZ! It can hardly be better than that! Here are a couple of early panels with rain:

2012121600_CON_GFS_SFC_SLP_THK_PRECIP_WINDS_018 — The 6 h ending at 11 AM today (unbelievable to me that its STILL raining in the mod then! Its like the “Miracle in Albuquerque” yesterday when the AZCats beat Neveda but had to score two TDs in the last 90 seconds to do it, doesn’t seem possible, will turn off TEEVEE and go do something else (as a friend really did. But there it is, its still raining here this morning, and a there WAS a miraculous win:

2012121600_CON_GFS_SFC_SLP_THK_PRECIP_WINDS_084 — Valid for Wednesday morning at 5 AM AST. This is the rain accumulation in the prior 6 h indicated by the area of green.

2012121600_CON_GFS_SFC_SLP_THK_PRECIP_WINDS_240 — Valid at 5 PM AST, Christmas Day. This follows a short break of several days, a break in which people get lulled into thinking its the end of the rainy spell, but they would be so WRONG! The rain shown here (green areas) is that rain the model believes has fallen in the prior 12 h (the period of rain lowers in resolution as the model gets farther away from its starting point; 6 h has become 12 h of rain areas.)

Go here to see them all, from IPS MeteoStar again. Too many rain panels; too little space. Quite the Big Bopper at the end of the run, too, on New Year’s Eve! One now wonders if after all the drought we’ve had, the sunny, comfy days, we’ll hear, after the next two to three weeks go by, complaints about how wet and cold its been? Humans: we’re like that. Me, too. I like complaining, especially about sound walls.

In sum, we are in a “bowl game”, a “trough bowl” where storms will be collecting off and on for the foreseeable future.

Be ready! It is the author’s experience that in some cases like this, the storms over a period of weeks, intensity, kind of go through a crescendo of sorts before the pattern changes back to dry again. Hope so. This would be great as an AZ drought buster.

The End.

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.

DSCN3411 — 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.

DSCN3409 — 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.

DSCN3351 — 2:28 PM. Stratocumulus top the Catalinas and water-covered rocks glisten in the the brief sunlight (look above road).

DSCN3353 — Also at 2:28 PM, farther north along the snow-capped Catalinas. So pretty.

DSCN3330 — 1 PM. Example of the summer-like appearance of our cold Cumulonimbus clouds yesterday, this one over the city of Tucson.

DSCN3383 — 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.

annoted cropped spag_f240_nhbg — 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.

Rain and when today

For those in a hurry: no rain before 5 PM AST, rain beginning between 5 PM and 8:42 PM; most of rain after midnight into mid-day. Since people forget, I’ve added a musical reminder there: “After midnight, we’re gonna let it all hang down.” Could be that incoming front talkin’ to us.

It will also be a fantastic day for clouds, probably some nice lenticulars today downwind of the Catalinas and elsewhere as the wind strengthens above us. Keep your camera handy.

For retirees, or others who have a LOT of time….

The long story line about how to forecast when

Its ALWAYS fun and a challenge to try to foretell when the rain will start to fall by the clock. Did some radio work like that in Seattle, i.e., “rain beginning between 11 AM and 2 PM”, “no rain before noon”, and also for the Washington Husky baseball and softball teams, when to take the tarp off, resume play, when put the tarp on, etc.

Those radio forecasts were made early in the morning on weekdays (KZAM-FM, 1982) and weekends (the latter during Weekend Edition on KUOW-FM, an NPR affiliate, 1987-1992). It was thought that such a forecast, given early in the day, would be the most useful one for a listener planning his/her day if it could be done well enough. This would be ESPECIALLY true on weekends when the listener could do whatever with his/her time rather than be in a building all day at work. But, could you do it well enough using the surface obs, weather maps, satellite imagery, and model forecasts generated the evening before, such as they were in those days. It was deemed a forecasting experiment in those days. It wasn’t being done elsewhere in SEA.

BTW, there was no weather radar in Seattle during those days if you can imagine such a thing.

However, I will also add that radar is really not that useful in SEA anyway since forecasts for the next 8-12 h is a window of time in which radar can’t be used, for example if the incoming rain is still off the coast of Washington! Reading the sky was much more important in determining how close the rain was, integrating that interpretation with the satellite imagery.

Or those days when showers would form that aren’t present in the early morning when you’re giving your forecast. The passage of a front in Seattle, BTW, is usually followed by a brief clearing followed by passing showers, unlike say, back East where once a band of rain goes by, that’s it for the rest of the day.

So, here we are in Catalina facing a great storm, our best of the winter. How close can you come to getting the start time here in Catalina? That’s the game. Today, the models are SO MUCH better, you have to look at them carefully, and know whether they run a bit fast in bringing in rain, and if there are any significant errors built in.

OK, here goes the first look, based on the passage of the core of the jet stream at the 500 millibar level, around 18,000 feet. The criteria that rain starts when its overhead and after it passes was developed during the early 1970s whilst the author, a forecaster, was working for a HUGE randomized cloud seeding experiment in Durango, Colorado. It was found that almost no precip fell in Durango before the 500 mb jet passed (95% of the wintertime precip there fell only after this happened). That study was later expanded to the ENTIRE US and it was found that wintertime (November through April) precip in the interior of the Southwest also followed that Durango criteria very closely; it was almost a black and white predictor.

So, let’s look at when the jet passes over us here (using IPS MeteoStar’s great forecast renderings again) and see what time it goes by (of course, in this era, the models also “know this” relationship; not so well in the early 1970s).

annotated 2012121300_CON_GFS_500_HGT_WINDS_024 — Valid for 5 PM AST today! Note the coloring. It shows where the velocity of the wind is higher and lower. Yellow, browns and reds are highest.

annotated 2 2012121300_CON_GFS_500_HGT_WINDS_030 — Valid for 11 PM AST tonight. Should be raining real good by now; jet has passed overhead and is to the south and east of us.

Like Seattle in some ways, this early onset of rain is from clouds for the most part, are ones that haven’t formed yet! They’ll be forming and filling in to the southwest of us and here, deepening as this big trough works inland toward us.

Next, if you were to measure the movement of the frontal rain band now in southern California over the past 12 h or so with a ruler, or piece of paper, you would find that at its present rate of movement that frontal band would be here around 10 AM tomorrow. So, you would have rain starting in the evening, peak rain in the morning. Done.

Now after this simple exercise, let’s see what the BEST model has in mind for the rain start, that from the U of A, processed by their intimidating “Beowulf cluster” (you can call it up here) based on data from 11 PM AST last night. This should be a very accurate forecast, and we hope resembles what was said above; no rain before 5 PM, but raining soon after that. (BTW, I have not looked yet; part of the “game” today; can you do as well as the model with a simple approach?

OK, here is the coverage of rain expected by 5 PM AST in the U of A model: not much, but its upwind.

annotated 5 PM AST Dec 13th 0001QC — Coverage of rain by 5 PM AST. Not much.

annotated 9 PM 0001TQ — Rain coverage by 9 PM tonight. Should have rained some to be redundant.

In sum, that simple technique was not so bad.

The main frontal band is still to the west at this point, 9 PM AST, and it doesn’t pass over until after midnight. Then the rain lingers into the mid-morning to early afternoon. Amounts still look VERY substantial. This model projects around a half an inch or more here in Catalina by tomorrow night. The range of values, given the various uncertainties in models and clouds and weather, bottom amount 0.25 inches (only 10% chance of less), top amount, an inch (only 10% chance of more), these percentages generated from this keyboard, BTW.

Here is the Beowulf total storm rain ending at midnight tomorrow night:

What’s after this?

Mods still showing spate of storms over the next couple of weeks, this one not a one-hit wonder. And there’s support for these storms in our venerable ensembles of spaghetti. Main brunt of storms: California. Expect to read about them.

But are our rains too late for our spring flowers? Dunno.

The End, at last.