Something to blab about at last. The computer models show a small area of low pressure breaking off the main jet stream and setttling over Arizona for a few days. Arrives on Monday, May 7th, then hangs around for a couple of days before moving off. Rain here? Doesn’t look like it now, but there should be some high based Cumulus, and one or two high-based thunderstorms over the mountains, maybe some Altocumulus here and there, too.
The happy part of this is that this time of year weak lows aloft like this one can produce a boatload of rain in the droughty areas of eastern New Mexico and west Texas when they interact with that Gulf air sloshing northward and westward into those areas. That happens after this forecast map. Let’s hope so. See below from our friends at Environment Canada for the afternoon of May 7th:
However, and pretty confidently predicted a huge bubble of warm air arises over us in the days. This in the longer term NOAA WRF-GFS model rendered by IPS Meteostar below. The last of the snowbirds will be scurrying off to their northern climes when this hits since temperatures are likely to ascend to over 100 F for a few days (a preview of normal June weather). Get ready.
Errata
Mr. Cloud-maven person misspoke recently when he asserted that May was our driest month. Below he reprises the Catalina monthly rainfall averages for himself and his two other readers.
Kind of got distracted with chores after the big trip to NC and didn’t get to this until today… If you can remember as far back as April 26th, we had a “FROPA” (“frontal passage” in weatherspeak) that day. The U of A weather model indicated beforehand that the bases of the clouds last Thursday would lower to the tops of Samaniego Ridge.
Well they did, though it seemed in doubt for a time, and occurred a bit later than the model had predicted.
Also, a few drops came down here late in the morning; more precip was visible to the north of us and that was reflected in the NCAR precip estimate for Arizona the following morning, an estimate that suggested the heaviest rains were up to half an inch just 150 miles away.
Here are a few of last Thursday’s clouds with some commentary.
Row of Altocumulus castellanus top lower center.
These clouds came in two separate segments, the first batch were at Altocumulus levels, some 12,000 feet above the ground according to the TUS balloon sounding that morning at 5 AM AST. Those were the clouds that produced the sprinkles around 5:30 AM. Poor snowflakes melting into drops had to fall such a long way!
After a brief clearing, a surge of lower Altocumulus and Stratocumulus came in. For a time, they looked awful threatening, and appreciable rain could be seen falling from them to the north. They produced a few sprinkles here in the late morning and early afternoon about the time the clouds had lowered (as predicted by the UA model, to the tops of Samaniego Ridge to the east).
In the distance is Altocumulus opacus virgae, that is considerable precip is dropping out of them.Here the faint whitish cloud ghosts near splotches of the Altocumulus clouds are due to ice crystals, indicating that these clouds are colder than -10 C at cloud top.Our regular neighborhood cloud, an Altocumulus lenticularis formed downwind of the Catalinas in the usual spot after most of the Altocumulus had departed.After the brief clearing, a surge of threatening looking Stratocumulus invaded the sky. Rain can be seen falling above the horizon to the north.
Why didn’t they rain more?
The answer, as always here, is that the tops were much shallower, and therefore warmer, than those early Altocumulus clouds sporting considerable ice at times. You can be sure that those Stratocumulus clouds over us had tops warmer than -10 C (14 F), a general threshold for ice formation around these here parts. (Over the oceans, where the drops inside the clouds are larger, the threshold temperature for ice formation is higher.)
Just to the north of us, where rain was occurring, you can be sure that the tops sloped upward in that direction, becoming colder than -10 C.
That second batch of lower clouds looked dark and threatening, but lots of times with lower clouds its because they have higher concentrations of drops in them, not because they’re especially thick as you might guess at first. The droplet concentrations in those dark Stratocumulus might have been twice as high as in those early higher, Altocumulus clouds.
Drops in clouds with higher droplet concentrations, say due to smog, reflect more of the sun’s light off the top. That makes them darker on the bottom, and because they are then also harder to get precip out of, they last longer.
This is a real problem, BTW, for climate models, since longer lasting clouds reflect more light back into space and in that sense, and help counter the global warming expected from trace gases like CO2. But, would you rather have ugly clouds and smog infested skies and a cooler planet, or clean skies and clouds and a warmer planet?
The weather ahead
No rain in sight. But a big heat wave, probably temps around 100 F now looming toward mid-may. May is our driest month, BTW, averaging only a quarter of an inch.
Who can forget those profound words of Aerosmith and Steve Tyler, “I’m BACK in the saddle again”? Just the way he says, “I’m BACK…” is really something. Well, if you can’t remember anything anymore, here’s a reminder. Wasn’t that great “rockumentary” movie by Rob Reiner, “Spinal Tap” about these guys? BTW, pilots on VFR flew through cloud saddles between turrets all the time… So, there really are “cloud saddles.”
First of all to start today, you budding cloud-mavens out there should, as always, be reviewing yesterday’s skies here to make sure you got all the clouds down in your cloud log, a service provided for you by your University of Arizona Weather Department. Since this link is overwritten each day, you probably should go there now.
In the meantime, while you’re scrutinizing that time lapse film, a cool front will go by this morning. Nice, except no rain outside of isolated sprinkles from mid-level clouds like….Altocumulus opacus virgae, you know, those dense loooking clouds with little snowstorms under them meaning their tops were colder than -10 C (14 F).
Later, after a brief gap in those mid-level clouds, some honest to goodness LOW clouds are supposed develop just after the front goes by later this morning. How do I know that? I cheated by going to the Wildcat Weather Department model results produced by the MASSIVE Beowulf Cluster and saw that clouds are supposed to get low enought to top Samaniego Ridge by mid-morning. Check the sounding predictions here if you don’t believe me. You’ll see the temperature and dewpoint lines pinch together at sharply lower altitudes beginning around 9-10 AM AST, with cloud bases predicted to be down to about 7,000 feet!
Haven’t seen cloud bases (bottoms of Cumulus and Stratocumulus) as low as that since the last rain which I missed because I was driving mom all the friggin’ way to Asheville, NC, and back to see my brother in his “new life” there. There’s a lurid story behind that new life, one that you would naturally be quite interested in, but it shall remain hidden from view.
But why don’t those lower clouds that move in and top our Catalina Mountains rain/snow? Tops too warm, predicted to be warmer than -10 C, so, no ice can form, a necessary ingredient for stuff to fall out the bottom. You probably knew that already, and I am beginning to feel a little useless. Oh, well.
Here’s a nice plot of today’s weather around the SW and the satellite cloud scene at 5 AM AST from the U of A (again): Wow! Rain drops hitting roof now, 5:37 AM! Overhead cloud tops still colder than -10 C!
Remember, if you are an intelligent person you will NOT CALL THESE FEW SCATTERED DROPS “DRIZZLE”!!!!!!! Its a rain shower, a very very light one, that you might “code” as RW— (three minuses). Drizzle drops float in the air, and are close together; these are not. There are IMPORTANT cloud reasons for denoting this difference. Some day I will tell you the “science story” about a well-known scientist, really considered the best in his field, who told me to leave his office and never come back after I informed him it had been drizzling outside. So, I Mr. Cloud-maven person has some “drizzle baggage”…..he is carrying around.
Note the gap in clouds over us now and that little scruff to the west. Those are the lower clouds that will move in later. Below this, our Tucson sounding for 5 AM AST, where you can see that the tops of these Altocumulus clouds are around -20 C (-4 F). Bases are indicated to be around 15,000 feet above sea level, or 12,000 feet above Catalina. Poor drops have to fall such a long way in such dry air. No wonder only the biggest ones, likely HUGE snowflake aggregates, or maybe even “graupel” up there, made it down.
Usually when you get carried away and expect something unusual to happen, it doesn’t, like that girl I thought liked me but didn’t (there have been a number of those…) Yesterday, carried-away Mr. Cloud Maven person mentioned the possibility of tubes in Cal. Here’s the report in the Big Valley near Merced, CA, from yesterday. Big hail, too. I am pumped! Spiking fubball now!
0535 PM FUNNEL CLOUD ATWATER 37.35N 120.60W
04/12/2012 MERCED CA PUBLIC
3 DIFFERENT FUNNEL CLOUDS IN THE ATWATER AREA
0605 PM HAIL ATWATER 37.35N 120.60W
04/12/2012 M1.75 INCH MERCED CA AMATEUR RADIO
Official name of tube-producing clouds? Oh, something like, “Cumulonimbus capillatus incus (has an anvil) tuba.”
Actually, its not terribly unusual to have tubes in Cal when the air is extremely cold up top over Cal in April and May, and that’s what we have now. Take a look at this nice, compact map from San Francisco State Former US Hippiedom Capital Weather Department for last evening at 5 PM AST. At San Francisco, its -29 C at 500 mb, very unusual for mid-April. (Actually, they got some real nice maps there.) Combine that with the strong sun on land surfaces, and voila, Cumulonimbus galore!
Also, if you look carefully, you will see that where there is no data, over the Pacific Ocean, the 500 millibar pressure contours are nice and smooth . But notice how “nervous” they get once crossing the coastline where there is data. I think really it has something to do with the interpolation scheme that try to place the contours exactly at the right spot between the real data; that algorithm may be a little primitive. Kind of funny in a way.
That cold core of air is heading for Arizona, and no doubt some April low temperature records will be set, such as lowest maximum, and likely a few minimum temperatures before this passes on into the Plains, with no doubt true severe weather there the result of that. And we, too, will have some Cumulonimbus clouds, lightning here and there around the State.
Below the SFO State map is the forecast from IPS Meteostar showing where this mass of cold air will be later Saturday at 5 PM AST, northern AZ. U of WA WRF-GFS mod thinks rain will be occurring here just about ALL DAY on Saturday after beginning around dawn! That would be a heckuva cold day, winter-like, with temps in the 40s-50s here at 3,000 feet and we’d have those pretty white Catalina Mountains afterwards. Sure seems like 0.20 inches is in the bag for the bottom of this rain event, with maybe 0.50 inches being at the top here in Catalina.
Yesterday’s line of enhanced virga in As deck at sunset
Now here’s an odd feature. Looked at first that it might have been due to an aircraft passage in that streak of Altostratus, but then I rejected that thought, as I can do. I came to believe somewhat confidently, odd as it is, that it was natural. Natural linear features in clouds are fairly common. Here it is, in case you missed it:
Things are falling into place. Remember the spaghetti from a week or more ago, in which it was clear, or at least at attempt was made to explain to both readers of this blog, that a large trough was almost certainly going to be along the Cal coast? We intuited that from the lack of spread in some contours in that “spaghetti” plot along the West Coast some week or more in advance.
Well, that trough is truly turing out to be a behemoth, a gigantosaurus for April. The people of California are going to be very excited today and tomorrow about cold, showery weather, mountains of snowfall in the mountains, maybe a funnel cloud or two in the Sac or San Joaquin Valleys. Here is that trough as shown on today’s 5 AM AST 500 millibar map from the U of WA weather department, the one prophesized with high confidence so long ago:
However, for many days after that, the models did not think the rain in Cal was going to get here. Of course, still being in the cool season, our rain is nearly all dependent on whether the jet stream in the middle levels (500 millibars or about 18,000 feet above sea level) is able to be over or especially, south of us here in Catalina.
But lately, in the forecasts, been shifting the jet southward and rain has started to show up in two or more recent model runs, always a good thing. You may also remember that in our spaghetti plots back a week ago, it was not clear in the models where the Cal trough was going to go after it bashed the West Coast. Hence, while things were clear for Cal (actually, they were going to be cloudy and rainy), they weren’t so clear for here until lately.
From the U of WA, this for Saturday morning (colored splotches denote where the model thinks precip has fallen in the prior 3 h); below, the jet stream at 500 mb from IPS Meteostar for the same time.
Yesterday’s clouds
In case you missed them…. Cumulus and Stratocumulus, punctuated with a splash of Cirrus fibratus undulatus (Cirrus with rolls, showing something akin to swells in the ocean in the atmosphere). The wind at Cirrus level in that shot is blowing from left to right. No ice falling out in Cu and Sc; too warm at cloud top. Only about -5 C (23 F) or warmer.
Apparently the castellanus formations went over during the nighttime hours when we couldn’t see them…
But it was a fabulous day again of interesting high and middle cloud flecks anyway. Below, a reprise of yesterday’s clouds starting with that delicate patch of Cirrus passing over the Catalina Mountains with its tiny fibers of Cirrus uncinus embedded in it. I have also included two sinister crossing contrails. Who knows what evil lurks there? Perhaps they’re marking a target of some kind, or filling out a questionnaire with crosses instead of check marks. Oh, well.
Later, as the sheet clouds of various Cirrus, Cirrostratus, and even Altostratus with virga cleared off, we got into some scattered lenticulars, some of to the distant north, and with our usual friend downwind of the Catalinas, shown in the last two shots. It was able to hang on for several hours, right past sunset.
Again, for the whole day’s cloud excitement, a great place to go is to our very own U of AZ Wildcat time lapse movie. In the late afternoon of this movie, you can see some great Altocumulus lenticularis clouds hovering over and downwind of the Catalina Mountains, occasionally shooting upwind as the air moistens in the humped up airflow, and you can get a sense of how little the air is pushed up in lenticular clouds from this movie.
(Once again the caption function has quit in WP before I got to some of these. My apologies.)
The weather ahead
Gee, “dusty cold snap” is beginning to look more like “muddy waters” as the later model runs dip the jet stream farther and farther south over us on the 14th and 15th. Check this forecast of the precip hereabouts from the U of WA’s WRF-GFS model run from last night, showing a bit of rain HERE Saturday morning (colored areas of map). Sure hope so. Terribly cold air with this, too, for mid-April. Likely some low temperature records will be set in the State somewhere for this time of year with this.
The End.
Tiny Cirrus uncinus, top center, Cirrocumulus top right with,oh, maybe Cirrus fibratus (has linear fibers) lower left.Cirrus uncinus.Altocumulus lenticularis.
Altocumulus lenticularis continues in place as sun goes down
Lots of nice Cirrus clouds yesterday, but no Altocumulus castellanus later in the day yesterday as it was asserted there would be. Only a flake or two of Altocumulus “uncastellanus”, (flat-as-you-can-get lenticular) clouds off in the distance (see bottom of page). BTW, I obsess over being right. I thought you’d want to know that about me since you come here every day and I am part of your life now. So, I made up the word “uncastellanus” because it sounds like in some way I might have been right about yesterday if you are reading quickly.
BTW#2, as per usual tendencies, the bottom of the moist layer where the Cirrus clouds were yesterday did slide down toward us during the day, from about 24 kft above the ground at 5 AM and -34 C to 21.5 kft and -27 C at 5 PM, the latter still pretty cold for clouds comprised of droplets, but they were there.
Below are a few “character of the sky” photos from yesterday. If you want the whole day, go here to the U of A time lapse. In this movie for yesterday are a few spectacular Cirrus castellanus clouds just after 11 AM AST. You’d swear they were real Cumulus clouds at first, but then you see them moving along at the same speed as the Cirrus clouds, glaciated with fall streaks beginning to come out as they go by.
You’ll also see in this movie, a lot a wind shear, changes in wind direction and or speed, with height, quite at lot visible early on. It will be easy to see how those trails of ice crystals get skewed away from the parent cloud producing these sometimes incoherent patterns when viewed from below.
Expecting castellanus TODAY, dammitall!
I think you can kind of sense my ferocity here about getting things right… A LOT of weatherpersons are like this, so its not just me.
As a potent trough blasts into Cal today, AZ will be in the rising motion part of that trough. So what happens? The air temperatures aloft begin to fall as the subsiding air pattern over us lessens and moves off to the east. With that tendency for subsiding air gone, some layers of the atmosphere will develop larger drops in temperature (lapse rate) as you go higher, a situation ripe for castellanus clouds, ones that look like miniature clouds that have been on a growth hormone. Those clouds (Ac cas) are probably my most favorite clouds, itty-bitty towering Cumulus clouds and so I do have a tendency over predict them based on a desire to see them. You can see what the TUS sounding is supposed to do here from the U of A model run. You’ll see the temperature falling just that bit over us late in the day. Well, it will be interesting to see what really happens!
Lots of other kinds of clouds are likely, too, such as a patch of Cirrocumulus, more Cirrus, and a lenticular here and there as the winds continue to increase over us. Gee, with the air coming from so far to the south, maybe even a scruff or two of small Cumulus clouds may show up, too, though Mr. Model doesn’t think so! Quite a cloud day possible.
Due to the high altitude the Altocumulus are likely to be at today, above 15, 000 feet above the ground, they’ll likely be cold enough (tops colder than -10 C, 14 F) to produce ice crystals and snowflakes, which we will see as virga coming out. Again, a fabulous sunset is possible because of the presence of more than one cloud layer.
Still only a dusty cold snap in the offing as the main upper trough bashes Cal Thursday and Friday before settling in over AZ on Saturday and Sunday.
Cirrus spissatus center (mostly).Altocumulus "uncastellanus" clouds begin to appear. I am somewhat happy since clouds composed of droplet are beginning to be present.Another Altocumulus "uncastellanus" lenticularis in the distance with Cirrus clouds.Another nice sunset, ones with mostly Cirrus spissatus (bloby Cirrus)
BTW, if you’re still interested in beer and clouds after yesterday’s blog about CIrrus being “on tap”, get this book:
Clouds in a Glass of Beer: Simple Experiments in Atmospheric Physics, Dover Publications, by Professor Craig Bohren. In spite of having an interest in beer or perhaps because of it, he is a Distinguished Professor Emeritus of Meteorology at Penn State University, one of the leading party schools in America. Writes about optics, too, a real atmo optician. Kidding aside, his book above is one of the best you can get on how the atmo works and has been popular for decades; was updated in 2001.
I forgot about it, darn, but added it to yesterday’s blog to “go with the theme….”
Yesterday and today
Nothin’ but filmy Cirrus clouds yesterday enhancing the skies over Catalina. Here’s are two examples. BTW, if you were really noticing, they tended to be thicker and more widespread to the north, as in the second photo, closer to the main jet stream up thataway.
Same stream of moist air at high levels continues over us, but, what happens over time with these high level streams of moist air? They tend to lower in height as time goes by. Here’s the stream in this loop from the U of WA Huskies Weather Dept.
So, today, we’ll likely see some mid-level droplet clouds, not all ice clouds like Cirrus ones of yesterday, and because its relatively warm up top, those droplet clouds tend to be turreted, i. e., Altocumulus castellanus (has a base) and floccus (base is evaporating upward). Both types indicate the same thing, really, that the atmosphere is a little “unstable” up there; updrafts are easily produced when the cloud forms and a little heat is released in the condensation process.
It looks, too, like those Altocumulus clouds will be around with the Cirrus at at sunset today, and you know what that means: lots of color so charge those camera batteries, cross fingers. Could be especially spectacular.
Cal-AZ storm update
The long, and confidently predicted (think spaghetti here) and unusually strong trough and storm for April 12th is still in the cards for Cal. AZ pcpn, though plentiful for April over a couple of days in the north, may not reach us here in Catalina, and if so, will be minimal it now appears, maybe a few hundredths. Look for dusty breezes for sure after the 12th. Check this loop out for all the details, again from the Huskies.
No, Cirrus is NOT a microbrew as you may have thought from the title and if you were visiting this site for the first time. (and to continue being juvenile from yesterday’s “Dusty Parhelia” submission because that’s who I am….)
In fact, Cirrus clouds are the exact opposite of a microbrew. Cirrus is a high CLOUD, 15,000 to 45,000 feet above ground level, lower in the Arctic or when its cold, higher in the Tropics or when its warm, like today here in Catallina. They’re composed of ice crystals with some momentary exceptions at the time of formation. To continue a theme, there are no “ice crystals” in beer; beer is also generally found at ground level.
Q. E. D.
BTW, if you’re still interested in beer and clouds, get this book:
Clouds in a Glass of Beer: Simple Experiments in Atmospheric Physics by Professor Craig Bohren. In spite of having an interest in beer or perhaps because of it, he is a Distinguished Professor Emeritus of Meteorology at Penn State University, one of the leading party schools in America. Writes about optics, too, a real atmo optician. Kidding aside, his book is one of the best you can get on how the atmo works.
To sum up, it should be another fun day of Cirrus cloud viewing for you and me. What kind will we see?
Yesterday’s clouds
Man, yesterday was great! Some unanticipated Altocumulus castellanus and floccus, middle-level clouds with little turrets, many having long fall streaks of snow (virga) rolled in during the afternoon underneath the higher Cirrus clouds, keeping the temperature down a bit. Here are some shots of what went overhead, in chronological order, in case you missed the “show.”
The show ended with dessert, another one of our gorgeous sunsets; they are particularly so when two or more cloud layers are present. In those case, you see the residual scattered light that has passed through the lower part of the atmosphere when the sun sets, turning the lower clouds gold or orange (the longer, “redder” wavelengths of light are still making it through) while the higher ones, where the sun’s light is not so scattered in passing through the atmo, are that bit lighter in color, white before this last photo. The greater the height difference in the clouds, the greater the differences in sunset colors between them. When you add shadows and highlights where the sun is striking the clouds, well, it doesn’t get any better than this. OK, I am feeling lazy now about captions; been up since 3 AM something. Can YOU name these clouds? If not, just enjoy.
