Author: 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.

Rain, snow (s), extreme cold ahead in mod run (pretty worked up today)

Was going to rest brain today, not blog-blab, but then went to mods; brain rest over.

“Holy Smokes!”, “Good Grief!”, my modest brain erupted with when perusing the 00 Z1 (5 PM AST) WRF-GFS model run this early AM.   If the predicted features verfify over the next 15 days, what appears to happen beyond that, this could be one of the most severe January’s in the Southwest in decades.  Yikes.  And our “test the effects of flapping butterfly wings on the model run” (figuratively) “spaghetti” plots from NOAA, those slightly perturbed/disturbed model runs,  seem to support last night’s ACTUAL run, at least into the first two events described below2.  “Hence”, as they used to say, the excitement this morning from this keyboard, but maybe some dread, too.

Quickie overview for Catalina

(taking the current model run (00 Z) at face value:

Jan 7th into the 8th:  Some rain, maybe a tenth or two.

Jan 11th-12th:  rain changing to snow, total precip maybe half an inch, with an inch or two of snow. Post event, temperatures dropping into the 20s at night, lower in washes and such.

Jan 16th.  Another chance of snow, doesn’t look like as much precip as the prior event, but colder yet afterward.  Temperatures lower yet, could get into the lower 20s, teens in the washes.

Furthermore, the pattern doesn’t appear to break after this last storm on the 16th.  It remains cold here through the end of the model run on January 20th.  As you likely know by now, once the jet stream gets into a pattern, it likes to keep it going.  No one knows why, or when it will break.  If we did, our longer term forecasting would be better.

Some more discussion below of this forecasted pattern, one that could lead to one of the more severe Januarys in the West in some decades.  While precip is always dicey here until the last moment, the exceptional cold seems very probable.  Be ready!

Here’s what the model (as usual, rendered here by IPS MeteoStar) has churned out for us in the way of rain/snow events for us,with the storm formerly mentioned here as arriving on the 8th, now arriving on the 7th.   (Heck, for awhile it was GONE!) This series of three trough/storm events shown below might be thought of as cool, colder, coldest.  Not so good as a series if you’re visiting here to enjoy warm weather.

Valid for middle of the day, January 7th. Not a bad storm, but not a great one, either, but good in the sense it keeps the stream of storms up after a week’s break. Maybe a tenth or two of rain.

 

Here’s the next one, valid for the evening of the 11th, and this one starts to get your attention, as in “Yikes! If that materializes, its snowing here!”:

Valid for 11 PM January 11th: Summary; yikes! So cold, rain turning to snow in Catalina, maybe a couple of inches. The thing to notice is the central contour number here, “12” lower than the “ordinary” storm shown above. The lower these numbers (contours where the height of the 500 millibar pressure is reached, the colder the air must be underneath it. The denser the air is, the faster the pressure changes as you go up. So a “540” contour represents really cold air in the Southwest moving into Arizona. I would not want to be a grapefruit in the few days after this goes by.

Finally, this, a brutally cold trough over us again, with the jet stream running a straight shot just down the interior of the West Coast from pretty much the place where Santa Claus lives, Barrow, AK.  Below, valid for the morning of January 16th:

Valid for 5 AM AST, January 16th. Egad! While precip might not be as much in the prior trough passage, this one looks colder after it goes by. Part of the contribution will be that the prior storm would have laid snow down over a vast area interior of the West, and that will help to keep the cold air blasting southward here colder here than it otherwise would be.

 

These particular depictions, especially the latter ones with rain and snow in them for us will be flopping around like a just-caught trout in a boat in the model runs ahead.  The main thing that seems “in the bag” for Arizona as a whole, is COLD air.  Cold to write home about.

Snow?  Of course, its less certain as the troughs wiggle around in the models, and to get that snow the apex of the troughs pretty much have to go over us and those little wiggles could take them to a bit to the east of us, making the coldest spells just dry ones.  That would be too bad, because if you’re going to have to endure cold, there might as well be some snow on the ground to play around in.

Now in a personal disclosure, one of the faults I have as a weather discussant, is to get TOO excited about extreme events that are forecast, rationality diminished, hence the “newsy” logo here:

“Right or wrong, you heard it here first!!!!”

It WILL be so much “fun-dread” day by day, to see if these things come to pass, how the models change these depictions above as new data are processed.  To repeat, though, be ready!

The End.

 

 

 

——————————————————————-

1Or, “CUT”, Coordinated UNIVERSAL time, as it is called today.  I hope those people on the edge of the universe are aware of our time convention.   Used to be known as GMT, Greenich Mean Time, starts at the 0th Meridian over “jolly old England.”  “Jolly”?  Huh.   Are they referring to Monty Python?  Rowan Atkinson? .

2Don’t forget to order your “I ‘heart’ spaghetti!”, tee shirt that shows you’re one of the scientific literati because “spaghetti” gives us insights into whether a model run is a bunch of crap (oops, “model excrement”.  New! Now available in down jackets….

Looking back, looking ahead: some climo info and a prospect for rain on the 8th

First, let’s look back and think of all the things we could have done better.  Its always great to mope around about things you did, but can’t change, but then, after a good mope,  jettison those thoughts, push ahead and vow to do better in the coming year, maybe fill in your weather diaries more completely, not miss that Altocumulus lenticularis in the lee of the Catalinas this year, learn a new language, thoughts that lift our spirits, for a time, anyway.

What could our weather have done better in 2012?

Rain more.

Check this annual chart out, kind of depressing except for July, August, and December (green bars are the observed totals):

OK, got that said, now let’s look at January, a month that is not beginning on a rainfull note.  Here is the daily occurrences of measurable rain over the past 36 years, the first 32 from Our Garden’s garden near Columbus and Stallion here in Catalina; and the years after that, a bit to the SE close to the water tank up at Swan and Wilds.  There will be slight differences between the two locations as a rule, and once in a great while,  large ones, as this past July when the Garden got clobbered with over 6 inches that month!

There’s some SLIGHT indication, after 36 years of data, that the chances of rain might increase after the 15th, but, like the early peaks in the first week, they might just be “noise”, statistical flukes that disappear with time, a lot more time.

What are the chances of a wetter than normal January, and even a wetter than normal first few months of the year (into May)?   Not that bad, surprisingly.  We had a dessicating January through May last year, and climate/weather doesn’t repeat those kinds of things very often on a year to year basis in the Southwest.  End of reasoning.

If you want something official, and not satisfied with my statement, here’s the Climate Prediction Center’s three month outlook for January, Febuary, and March of this year.  Remember, they also told us an El Nino was coming, then said it wasn’t…

 

The weather ahead

While the US WRF-GFS model run from last night (00Z run, 5 PM AST) still has us rainless for the next FIFTEEN days, the superlative Canadian Environment Canada model, while looking at the very same upper low center in the US model that passes to the south of us on the afternoon of the 8th, says it will have rain in it for us!  US mod says it stays dry here as it goes by over northern Mexico.   Here are the forecast panels from our Canadian friends for 5 PM January 8th:

Spaghetti maps guarantee a substantial upper level low/trough will affect us on the 7th-9th, too.  Not sure why its so DRY in the US model as it goes by on the 8th-9th.  I am guessing that will change over the next few model runs.

The End.

Mostly in absentia yesterday: contrails

Yesterday was as remarkable in its way as the day before in its generic beauty.  Delicate Strands and fibrous blobs of Cirrus in interesting shapes floated by overhead with nary a contrail to contaminate those scenes.  While our little part of the sky above Catalina, Arizona,  is a low contrail impacted zone of the sky, yesterday seemed exceptional.   It mgiht have been because, and since I am guessing here, will not check it out, those wonderful clouds and that moist layer they were embedded in was LOWER or HIGHER than usual, and the flight levels that the jets were flying in remained very dry so that they don’t persist.  Its the ambient humidity up there that makes them various lengths.  If its too dry, there is only that bit right behind the jet–recall Appleman (1951) and the Appleman diagram.

Also, the wind direction at flight levels helped; due west generally keeps those contrails packing airways just to the north of us and to the south streaming along beside us, not over us.  That always helps.

But, I didn’t really see much off to the north, where there are usually a half dozen or so on any “Cirrus-ee” day.

Was it because it was New Year’s Day and air traffic is unusually low because no one wants to travel because they wouldn’t be able to watch the Rose Parade and various football bowl games?  Don’t know, but maybe.

I have given you a LOT of things to think about, and while you’re doing that, I will post some evidence, contrail-less Cirrus skies.  You won’t find this kind of day we had yesterday along the Atlantic Seaboard on any day with Cirrus with all the jet activity.

7:53 AM. Here come those Cirrus clouds!
9:25 AM. Cirrus spissatus (dense Cirrus) approaches, the only kind of Cirrus in which gray shading is allowed.
11:16 AM. Quite oddly, whilst talking about a lack of contrails, I show a snippet of one here. It had quite the long virga trails. Those trails would have been composed of larger crystals that grew in the moist air in the exhaust of the jet.
They’re long because the air was moist below the jet, but just for that bit where it flew and hit a moist patch at flight level and below it.  Perhaps he was changing flight levels?
11:24, just eight minutes later, this same contrail segment. Estimating length of those trails, a kilometer, about 3,000 feet. What is also a bit odd, they’re hanging almost straight down below the original contrail for such a great distance before curving off. This tells you that over a fairly great depth, a few thousand feet, the wind did not change in velocity or direction, a bit unusual. You likely pointed that out to your friends yesterday anyway, but I thought I would mention it.
1:45 PM. Delicate Cirrus fibratus (more or less has straight fibers), and NO CONTRAILS. This was an amazing sight to me since you’re staring right out into one of the heaviest air corridors near us. Well, maybe on on the far, far horizon.
4:47 PM One of the most interesing/odd sights, this angular piece of Cirrus spissatus (popularly called, “Cis spis.”) I thought I would show off some camera razzle dazzle by pointing it at exactly the angle required to get an internal glint, a reflection, that points to that interesting Cirrus cloud I wanted to blab about.
5:04 PM. Same cloud almost overhead with a razzle dazzle glint-reflection pointing to the “tail”, that last bit of snow/ice crystals falling out of this Cirrus patch.
5:43 PM. Another one of the reasons we live here; our fine, fine sunsets, so many.
Here what you are seeing underlit are the tiny ice crystals that are in the last stages of being evaporated, once having falling out of their parent clouds higher up. Because they are now so tiny, and about to disappear, they have almost no fallspeed and kind of float at one level for awhile. You can see here how flat that is in the sunset. A new spec of parent cloud is also visible, one that has just formed and has no trails yet (slightly left of center).

The weather ahead?

There isn’t any.  Well, any worth mentioning right now.  Gotta get through this week or two dry spell somehow…

Will dredge up some January climo tomorrow or the next day.

 

The End.

 

Yesterday: a rare drizzle occurrence in the morning and later, gorgeous Cumulus-filled skies

First of all, Happy New Year to both readers! Thanks for hanging in there.

The weather ahead…

before a long diatribe about drizzle, followed by some pretty pictures with explanations:

Some picaresque Cirrus later today. Looks like next chance for rain is around the 10th-11th of Jan.

A rare drizzle occurrence

Cloud maven juniors were probably excited beyond description when they went out yesterday morning between 9 and 11 AM and intercepted a rare occurrences of brief drizzle here in Arizona falling from that low-hanging Stratocumulus overcast.  This happened after several very light RAIN (not drizzle) showers dropped another 0.02 inches, raising our storm total here in Catalina to a respectable 0.30 inches.

Drizzle is composed of drops barely large enough to cause a  disturbance in a puddle of water1, as though a large particle of dust had landed in it.  Drizzle drops nearly float in the air (should not be falling at more than about 3-4 feet a second), and in many cases of very light drizzle, the drops can float around like “desert broom” seeds. Visibility is usually lowered, things look fuzzy in the distance. Drizzle precip is so light it can’t produce even 0.01 inches except over periods of an hour or more.  Drizzle drops are also more uniform in size than the drops in rain, and are usually very close together.

While drizzle is common along the west coasts of continents in coastal Stratus and Stratocumulus clouds, its much rarer at inland locations such as here in Arizona, thus, the excitement over seeing it yesterday.

The reason why its rare in AZ?

Shallow clouds that drizzle must be what we would term, “clean” clouds; they don’t contain many cloud condensation nuclei and so droplet concentrations are low, maybe 50-200 per cubic centimeter (might not sound low, but for a cloud, it is). Clean evironments are found over the oceans and for awhile, in air coming inland along the west coasts of continents in onshore flow before it gets contaminated with natural and anthropogenic aerosols (smog).   Man, we are getting into a real learning module here!  Wonder if any readers are left?  Probably talkin’ to myself now.  Oh, well, plodding on. Nice photos below…far below.

Drizzle occurrences tell you a lot about the clouds overhead.  Not only are they low-based as is obvious (they have to be or the drizzle can’t reach the ground), but they are relatively shallow clouds no matter how dark they look.  Furthermore, and more subtle, they have larger cloud droplets (ones to small to fall out as precip) in them that must be larger than about 30 microns in diameter (smaller than half a typical human hair diameter).  When this larger size is reached in clouds, and those drops are pretty numerous, say 1000 per liter, they begin sticking together when they collide in the normal turbulence in clouds.  Those collisions with coalescence result in drops that fall much faster, bump into more drops, growing larger and larger until they fall out the bottom.

In a shallow cloud, those drops can’t get larger than drizzle drops, and that’s one of the ways you KNOW that they are shallow no matter how friggin’ dark they look.

—————-
Aside about rain not due to the ice process:
The largest drop ever measured, 1 cm in diameter, was observed in a Hawaiian Cumulus cloud that did not reach up to the freezing level!  Unfortunately, the authors of this finding did not publish their results and so did not get a Guinness record like me and Pete Hobbs did when we reported a smaller 0.86 centimeter diameter drop in Geo. Res. Lett., 2004–found them in Brazil, and again in the Marshall Islands–hit the pilot’s window like little water balloons.  Instead of being in a book with other famous people, like ones who can eat 47 hot dogs in 12 minutes, those researchers who encountered that larger drop in Hawaii sat on their finding! Unbelievable.

Strangely believe it, from lab experiments, drops bigger than 0.5 cm are not supposed to exist, but rather break up around 0.5 centimeters in diameter.  (hahahahaha, lab people). End of aside.
—————–

1Officially, 200-500 microns in diameter, equivalent to a couple or three of human hairs, maybe ONE or two horse’s tail hairs, to add a western flavor to the description.)

Yesterday’s gorgeous skies!:

Took more than 100 photos yesterday.  Was out of control, euphoric, thinking how great this earth is, maybe leaning toward thoughts of higher being and creativity therein, thus explaining the “creative” punctuation above.  Here are a few shots of those magnificent clouds and our magnificent, snow-covered Catalina Mountains.  First, those drizzle-producing clouds:

10:12 AM. Last of the drizzling Stratocumulus overcast. Patchy area of drizzle to west on the Tortolita Mountains here. The Stratocu gradually broke up after this time.

 

11:54 AM. Stratocumulus clouds still in charge, but lift here for a peak at the new snow on the Catalinas.
12:13 PM. First snow showers appear to the north-northwest as the stratocu deck begins evolving into Cumulus congestus and small Cumulonimbus clouds with large breaks.
12:35 PM. Snow showers from relatively shallow Cumulus race along the Catalina Mountains. These kinds of snow showers occurred right up until late afternoon.
12:37 PM. Snow and light rainshowers from shallow Cumulonimbus clouds also begin moving into Oro Valley before striking the Catalinas. Look at how similar these smaller clouds with their rain/snow shafts appear to our summer giants.
12:59 PM. Shower over the Oro Valley moves onto the Catalinas. Arrow points to a filament/strand coming out that is almost certainly composed of graupel (soft hail), something that was common yesterday from these clouds.
2:38 PM. HOWEVER, graupel often falls out of Cumulus congestus clouds on their way to being a Cumulonimbus without any sign of precip overhead, as here. This is because you are getting the result of the very first ice to form and fallout, usually those first ice particles are pretty rare in many of the shallow clouds as we had yesterday, and, because the updrafts are weak, they fall out as isolated little snowballs, too few to produce evidence of a shaft. But hang on, a shaft often, in the deeper clouds, imminent.
Also at 2:38 PM, looking northwest. A view of smaller Cumulus with the deep blue of the winter sky we love.
3:07 PM. “Congestus on the Catalinas.” You might ask, “where’s the ice?”, since yesterday all clouds reaching this size produced ice/snow/rain. Well, its on the other side (due to wind shear that carried the ice off toward the east. I think that’s the real reason why “the bear went over the mountain”, as we used to sing.

3:11 PM. Example of the medium Cumulus clouds (mediocris) that developed ice in them yesterday because it was so cold aloft, tops here colder than -12 C. (estimated).  Arrows point to ice, necessary for measurable precip here.
3:50 PM. Another modest Cumulus with plenty of ice (probably 10s per liter if you were guessing). Lowest top temperature likely lower than -15 C.

4:08 PM. I have no idea. This patch of ice cloud is left over, a “ghost” really, of a medium Cumulus cloud whose droplets evaporated. But what would it be called now? Altostratus translucidus cumulomediocristransmutatus? Cirrus spissatus cumulomediocristransmutatus? Silly, but I know of no name for such a patch of ice/virga
4:49 PM. You knew that on this cold day you would be treated to some of our finest scenes in winter, golden scenes of cloud-capped, snowy mountains, and later, those rosy under lit remaining small Cumulus and patches of Stratocumulus. What a fine day it was!

Not a bad storm, but not a good one, either

0.28 inches here in this part of Catalina, 0.31 inches at the bridge and Golder Ranch Dr., half mile away, 0.29 inches at Sutherland Heights.  Coulda been more.   Pima County ALERT gage reports here FYI.  Most there, 0.47 inches, Catalina foothills, compatible with the southerly flow; clouds bank up more on that side of the Cat Mountains when the flow is mostly southerly.  U of AZ rain network, here.

OK, I shouldn’t be the storm grinch…  It was great to get something when the models were often oscillating between zeroes and rain out a week or so from yesterday.

December is a benchmark for us: now with 2.11 inches of rain,  its the first month of this calendar year with above normal rain outside of July and August.  All of this has fallen since we fell into the “trough bowl” in mid-December.

Point, models!

The onset of rain here, that is the first drops, did not fall until about 6 PM, EXACTLY as the U of AZ Beowulf Cluster model run said!  It doesn’t get better than that.   The amount, too, was exactly that predicted, in the range of 0.10 to 0.50.  Think I’ll quit.  Yesterday at this time, me, myself and I were anticipating around half an inch, with a 0.20 inches as lower limit, one we just climbed over; 0.80 inches upper limit .  Also, thought the first drops to fall, in our little attempt to “Beat the Model” would occur before 5 PM AST.

The transitioning sky yesterday afternoon

Not much seemed to be happened yesterday as the Altostratus clouds thickened and thinned with the sun occasionally popping out strongly enough to produce shadows.

But, as a cloud-centric person, the only variety of human reading this blog, you may have noticed, even been awestruck by the drastic change that occurred between about 2:30 PM and 3:30 PM.  Started getting hopeful about some drops getting down in Catalina before 5 PM.   Here’s what happened, all due to a surge of moist air that started to come in below the height of the Altostratus in mid-afternoon, and that surge being associated with the approaching upper level trough.  First, two “before” pictures of a “stagnant” sky:

8:18 AM. Cirrus and Altostratus translucidus (in the distance)  also a mainly ice cloud) in a nice, radiating configuration, most likely due to perspective.
1:59 PM. Yawn. Sun bright, no sign of the drastic change hoped for. Clouds are Altostratus translucidus; too much shading overall to be called Cirrus, though a higher, separate layer of Cirrus was sometimes seen.

 

 

 

 

 

 

 

 

 

 

 

 

2:32 PM. Sky changing rapidly. Distant lower layer on horizon. Small Cu popping up around the Catalinas! Here we go!
3:03 PM. Sky changing fast! Looks a little threatening already. Stratocumulus forming under Altostratus opacus and translucidus. Altocumulus also present.
Photo title: Horse under a lowering sky.
4:20 PM. The further lowering of these cloud decks, with a new one with virga on the distant horizon to the southwest was too far away to get here by 5 PM, just as Beowulf said.

 

 

 

 

 

 

 

 

 

The weather ahead

Grim, in a word now.  “Trough Bowl” exiting right (east) for an extended period of time, so we’re more or less away from the storm track for awhile.  Gradual warming trend, of course, along with that.

HOWEVER, a fantasy storm has shown up, if you’re a fantasy weather forecasting league person, this one will get you a LOT of points.  Check this forecast out from the WRF-GFS 00 Z (5 PM AST) global data (rendered by IPS MeteoStar).  Summary?  Juicy.

Valid 5 PM AST, January 12th. Colored areas denote where the model believes precipitation has fallen over the prior 12 h. Blue regions denote especially heavy precip.

 Valid for the same time as the map above showing where the 500 mb trough is with all that rain (over LAX).

But, of course, we know when to laugh at progs like this.  Go to the ensembles of spaghetti and see if there is ANY veracity to a big trough in the upper levels, one that would HAVE to accompany a rain map like this.  “These are their stories”, to quote a TEEVEE line:

Valid for the same time as the 500 millibar (mb) map above. Not REAL hopeful, though there is some chance of verification as indicated by several of the red lines running across Baja. Look for this storm to come and go in the model runs in the days ahead.  Overall though, the big northward bulge in the red and blue lines suggest a storm-blocking ridge along the West Coast is the most likely outcome of this mess, with a trough over northern Mexico and the Rockies, the latter too far east to do us much good but keep the temperatures down.

 

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:

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!

 

4:20 PM. The young (left) and the old (right) , side by side.

 

 

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:

8:24 AM. Altocumulus overspreads the sky, briefly. Ac perlucidus translucidus (thin). Someday I think I will make you memorize ALL of the cloud names and their species and varieties.
8:59 AM. This beauty. It appears to be Cirrus of some kind (spissatus). But then yesterday I had written that there wasn’t going to be any Cirrus, and so I will term this, Altostratus translucidus altocumulotransmutatus. Pretty cloud, but ugly name (it really exists, and this patch really did originate via the glaciation of Altocumulus clouds.)
10:33 AM. Never have seen this sequence before. After the prior patch of ice cloud (some liquid cloud at top) moved off, a new wedge of Altocumulus (perlucidus) formed in the moist plume up there. Also very pretty I thought. Estimated height above ground, 18,000 feet, -25 C or even a little colder. Nature loves to form water drops before it freezes, as here, even at very low temperatures.
12:58 PM. Rise of the Cumulus machine…. Here, beyond Twin Peaks, is the first glaciating cluster of Cumulus/Stratocumulus responding to the cooling aloft and a bit of surface heating below.
2:04 PM. Locally, our Cumulus remained small, but in the distance is the icy tops associated with the line of sprinkles its not drizzle that came through later in the afternoon, enhanced by further Cumulus deepening around here as the afternoon progressed. Pretty sky.
2:38 PM. Heavier Cumulus bases line up against the Catalina Mountains near Charoleau Gap. Looking better for precip here at this point.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 


2:39 PM. A tell tale ice plume is amid these smaller clouds telling the observer that it is damn cold up there for such small clouds to produce so much ice (though the one that produced this little plume would have been taller than those around it) How cold? Estimate the top of the one that produced this was at least
lower than -15 C (5 F). Ice crystal concentrations? Estimate at least a few per liter of air at this time when you see an ice plume like this. Pretty soon you’ll get that Cloud Maven tee.

3:58 PM. By this time it looked very promising for a few hundredths of rain.
5:36 PM. But after all the bluster, just a trace of rain here.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

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

10:03 AM. Your really cold Altocumulus clouds; transitioned to ice shortly after this. Probably colder than -25 C.
1:32 PM. CIrrus spissatus, maybe it could be called an Altostratus translucidus since its quite thick toward the horizon.
1:32 PM. You got yer Altocumulus lenticulars (brighter white clouds below patchy Cirrus.
5:25 PM. The major band of high and some middle clouds exits south of Catalina.
No high clouds today, only low and maybe some Altocumulus/Stratocumulus formed by the spreading out of Cumulus tops.

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….

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.

—————–

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.

Middle and high clouds a plenty, day in and day out

Your Christmas Day clouds:

7:21 AM. Pretty nice underlit Cirrostratus I’d call it.
3:01 PM. Altostratus opacus-wallpaper, boring, etc.  A deep ice cloud here (though sometimes it can have embedded droplet layers identical in structure to Altocumulus clouds.)
3:02 PM. Altostratus translucidus (sun’s position is detectable). No sign of droplet clouds in that view of the sun. They would be discerned as little, dark cloudlets with sharp edges (the concentrations of droplets in clouds is always far higher than ice crystals. For that reason, the sun can be completely blocked by a cloud 1,000 feet thick, but an Altostratus layer 5-10 thousand feet thick, such as here, cannot.

 

More of the same types of clouds are streaming toward Catalina today (sat imagery with radar here), but the winds aloft are increasing as another upper level trough approaches, this one in two parts.  Today more Cirrus, Altostratus, and probably some Altocumulus with lenticularis clouds here and there, especially downwind of Mt. Lemmon, as one part of it goes overhead.  These clouds will be drifting off to the south of us over the next 24 h as the second trough approaches with much colder air, and lower clouds, bringing with them a chance of a little rain later tomorrow and overnight.   We should see Cumulus and Stratocumulus dangling icy virga by tomorrow afternoon and evening.  Any rain will be pretty light, likely not more than 0.15 inches.

The weather ahead

Still looking for more rain after this marginal rain chance tomorrow night.  But, mods now have rain moving in much sooner, before the end of the month, on Sunday, December 30th due to wild changes in model runs.  Formerly, the rain waited until early January.  View latest (06Z, 11 PM AST last night) run here.

Wildness?  Look below at two model runs valid for the same hour, 5 PM AST New Year’s Eve.  Sobering, which is probably a good thing on New Year’s Eve.

The Canadian model has our end of December low lurking off southern Baja (upper left panel below), while the USA model has it scooped up and merged it with another trough dropping down out of the north before it can get cut out of the flow.  Vastly different takes!

Take a look at these model depictions and have sympathy for your local weather forecasters trying to deal with this mess (“model divergence” is what we might call it,  to sound more scientific, but its really just a mess for us).

How to decide which one has more truth?

Check the spaghetti.

Sadly, this chart, also valid for New Year’s Eve, makes the low far off Baja less likely to be realized (as suggested by the few red lines wandering off the Baja coast), that is, the Canadian model calculations have come up with an “outlier” result, one not so likely to be realized, though not impossible. Dang! If that low had hung around off Baja for a couple of days, and THEN ejected northeastward,  as the prior model runs had been repeatedly showing until lately, we’d had the possibility for a very substantial rain.

Now we seemed doomed to something much less potent as a rain/snow producer, and very cold.


The End.