I was really happy for everyone out there when the skies were dotted with so many perfect examples of Cumulus humilis. It was like a numismatist finding a perfect Indian head penny. If you were like me, and I suspect you are, you were just going CRAZY taking pictures of those flat little pancake clouds. Those clouds were pretty much limited to about 1,000 feet (300 m) thick at most
Not cold enough for ice in them, of course, since the temperatures at Cumulus cloud tops were only around -3 ° to -5 °C (28 ° to 23 ° F, respectively). Around here, ice USUALLY does not appear in clouds until the temperature is lower than -10 °C at cloud top.
Yesterday began with some light snow falling on Mt Lemmon…well, it was falling downward TOWARD Ms Lemmon, actually. Fell out of some thick Altocumulus clouds up there around where the cloud top temperature is… what? OK, silly question for you, probably lower than -15 °C (5 ° F).
Let’s check the sounding to be sure, remembering that the launch site (University of AZ) was downwind of air flowing from the NW yesterday that went over the Catalinas, so a sounding at the U of AZ might suggest higher temperatures than this cloud was actually at since the air was probably descending before it got there.
Indeed, as just seen by me, the TUS sounding indicates that layer, up around 14 kft above sea level, 11 kft or so above Catalina, not a city, but rather a Census Designated Place or CDP, was “only”at -10 ° C.
I reject that as the temperature of the virga-ing cloud over Ms. Lemmon! Its a little too warm IMO.
8:41 AM. That white haze under the Altocumulus clouds is composed of ice crystals, concentrations probably a couple or less per liter of air. Likely stellar or plate crystals, ones that form at temperatures less than -10 ° C. Almost certainly no aggregates of crystals; concentrations too low to form “snowflakes” which are aggregates of single crystals. Snowflakes form when higher concentrations of crystals collide and get locked together, as in stellars, and their cousins, dendrites, that grow in a similar temperature regime. Dendritic crystals are usually seen in deeper clouds than these because those crystals have time to grow extensions in various directions, are not just “planar” ones. If the cloud is thin like this one, not much growth can take place in the droplet cloud and simpler crystals like hexagonal plates and stellars (Christmas card crystals) fall out. There is a lot of hand-waving here….10:20 AM. A horse named “Zeus” looks to see if any Cumulus clouds are forming over the Mogollon Rim to the NE, or, maybe he’s fixated on the horses in that corral below…
By afternoon, the skies over Catalinaland were spotted and dotted with spectacular Cumulis humilis examples. (The littlest shred clouds are Cumulus “fractus.”)
I’ve left the time of the photos off today. After all, there was only one true time yesterday, “perfect humilis time!” or as we like to say, “PHT.” Immerse yourself.
“BN”, sometimes referred to in the media as the, “Godzilla Niño” of 15-16.
Before, one year ago, the drought status as presented by the National Drought Monitor folks there in Cornhuskerland, Lincoln, NE:
First, a legend, no, not a story, though we could write one, “The Legend of the Ghost Niño of 2015-16“, but rather a guide to the colorful drought intensities on the maps below:
One year ago
Western drought status as of April 7th, 2015.
Now let us look closely below–you’ll have to–to see what the Big Niño has done to ameliorate drought so far THIS water year (since Oct 1):
Western drought status as of April 5th, 2016!
Of course, the giant low centers spinning around in the central Pacific sent a stream of large waves over and over again that blasted the Cal coast. That was expected, and verified. But not much else did. Drought should have increased in the Pac NW–recall it was forecast to be drier and warmer due to Niño conditions. Instead, the Pac NW had record amounts of winter rain!
Cal, especially, central and southern were to be slammed. Southern Cal residents were advised to consider purchasing sandbags in one media story last fall. And, of course, we here in AZ are profoundly disappointed; conditions have only improved some in the north part of the State.
Well, of course, there’s not one dry meteorological eye in the house after a bust of this magnitude. And when our best models predicted giant West Coast storms that looked like the kind we were expecting due to the Niño, even though they were 10-15 days out, they seemed sure to happen. CMP, bloated with confirmation bias, was sucked in several times this past winter.
Sure, we knew that Niño correlations with weather are not 1.00, that is, perfect, still, the “signal”, the size of the Niño, was so huge we figured it had to come through with those mighty storms striking the lower West Coast as happened in 1982-83 and 1997-98. Those correlations, as strong as they were, of course, were limited in number since these large events are rare. Those correlations will, let us say in place of cuss words, “degrade.”
Oh, me, what will we say when the next Big Niño appears?
The weather ahead
You’re probably pretty excited about the wind and very cold air just ahead. CMP is. And, with the jet stream at 500 mb (18, 000 feet or so–5.5 km above sea level) eventually circumscribing us with its charateristic moist lower region of air, we should just enough moisture for some isolated very light showers, probably just in the Catalinas, during the period of low freezing levels that hits late Friday and continues through Sunday. Low freezing levels mean even moderate Cumulus clouds could form ice, leading to virga.
Amounts could, at the most, only be a few hundredths here, and most likely we will be missed; precip just limited to snow flurries on Ms. Mt. Lemmon and thereabouts. The U of AZ mod sees the cold blast arriving late Friday after dark.
On the other hand, Saturday and maybe Sunday as well, will be good days for you to practice your ice in clouds detection skills in smallish Cumulus clouds.
The weather way ahead
Still looking to see at least two more troughs and chances of rain during the last two weeks of the month. NOAA ensembles suggest so. Best chances, 23rd-25th, and again around the 28th or so.
Some cloud shots from our little 0.01 inch rain day on Tuesday:
6:02 AM, Tuesday. A summer-like scene, complete with thunder frames the post dawn hours.10:35 AM. After the morning excitement cleared off, a pretty Cumulus congestus erupted north of Saddlebrooke town. There’s a hawk in the photo.12:12 PM. That Cumulus congestus and its sisters, were able to reach the level of glaciation, and wind shear, send a plume of ice downstream toward the east, and rain below that overshooting turret.2:36 PM. Pretty much the perfect cloud for ice in cloud studies. As the air warmed aloft and capped the Cumulus clouds, this one just poked up high enough to form some ice. It would have been a great sample to determine the temperatures and cloud conditions at which ice onset in clouds on Tuesday.4:16 PM, Tuesday. Those shadow and sun highlights that make our mountains so darned pretty. I just never will be tired of these views!
Since the forecast given HERE for large Cumulus clouds becoming Cumulonimbi did not happen last evening, it seemed appropriate to show some wildflowers as a distraction. First, a light, purple one of some kind; second, what we here call an “Arizona rose”, those fabulous blooms that form on prickly pear cacti. The photos below were, in fact, taken late yesterday afternoon as the forecast of the development of those larger Cumulus was failing to materialize.
Wouldn’t it be great if we could GM these to have long stems?!
Now that you’ve forgotten the erroneous forecast of large cumuliform clouds made here yesterday, I would like to point out that the cooler air up top has finally arrived in the pre-dawn hours today, and we do have Cumulonimbi in the area; even some LTG over there by Mt. Graham around 4 AM as this is being written.
However, bases are pretty high, 7,000 feet above the ground, and so only the central cores of the rain shafts are producing much rain to the ground right now. However#2, these are the kinds of situations that incredible photos of long virga trails during sunrise can be gotten. Be ready! The whole situation is moving east pretty rapidly.
Yesterday’s clouds
10:22 AM. Cumulus fractus and humilis topped by Cirrus spissatus enhance a blue sky.10:28 AM. Wow, a Cumulonimbus capillatus top can be seen just beyond Mt. Sara Lemmon! And it only mid-morning! This is a test. A patch of Cirrus has aligned itself above some small Cumulus clouds topping the Lemmon. We’re you fooled for a moment? I hope not.5:13 PM. More Kelvin-Helmholtz billow clouds at Cirrus level. Pretty rare sight, actually. Shows waves in the atmosphere. Don’t want to fly in them. This was about the greatest cloud excitement of the whole late afternoon and evening.6:06 PM. “Slab lifting” by our incoming upper level thingy has led to the formation of a couple levels of flat clouds, Altocumulus lenticularis, some Altocumulus perlucidus (honeycomb look), and some Cirrus perlucidus way up top. Some small to moderate Cu can be seen on the horizon. Was still thinking they might “pop” as cooler air moved over us. You might be able to see that some of the little cloudlets at Cirrus-levels started out as droplet clouds before transforming to ice. Ma Nature likes water so much it almost always develops first before ice even at temperatures below -30 °C. Pretty amazing, really.
Thunder just now! Wow. 5:20 AM. Sorry for the delay, had to go outside and check things out. Really will be a fabulous sunrise!
6:16 PM. Still thinking it might pop. Didn’t even see ice as that Cumulus turret declined.
Though the clouds faded as the sun went down, there were still some highlights on the Catalinas that made it a near perfect day.
6:17 PM. What’s to say? We’re so lucky to be able to see scenes like this in Arizona.
The weather ahead
Turbulent, changeable, unsettled through the remainder of April. More chances to add to our 0.73 inch total so far for this month. Stay tuned to your favorite media weather folk!
Yesterday was a great day both for airborne researchers studying the onset of ice in clouds, and for my followers to test their “ice” Q detecting abilities, to come up with a clever play on words there.
What was so great about yesterday’s clouds?
Well, they were real cold, bases up around 9,000 feet above Catalina (about 12,500 feet above sea level) at -7° C (19° F). Excellent. Nice data point.
Cloud tops?
This is what was pretty great for you and me; they didn’t overshoot much, the clouds were pretty flat, not very deep, not a lot of flight time needed climbing to cloud top to see what it was around here. That means that if you are flying around up there sampling clouds for ice content, that the tops you smashed with your aircraft were pretty much the ones at the temperature that the ice crystals you ran into later formed at. Remember, when cloud tops first rise up, they usually have little detectable ice (the ice crystals are too small for your instruments, or, they haven’t formed yet, takes a little time.
When there are big overshooting tops, an inexperienced, well, crummy researcher in an aircraft finding the ice, as it is usually found, lower down in the cloud, might put the origin of the ice at the temperature of the collapsed top, not at the lower temperature where it formed and the original top reached up to.
So, the lack of much overshooting made it a great day to assign the ice you found to the right cloud top temperatures.
What else was great?
It was a marginal day for ice formation here in the Catalina area, so you get a good data point on when ice starts to form in clouds given that base temperature. As the cloud deepens upward, more ice would be expected with the lower temperatures.
And, as noted by Ludlum way back in the 1950s, and by Prof. Battan right here at the University of Arizona which I did not attend, btw, that level at which ice and precip onsets changes from day to day (largely related to how warm (crazy isn’t it?) the cloud base temperature is. On days with warmer cloud bases, the ice onset temperature is also higher. For example, in summer here, its not unusual to have ice onset between temperatures of -5° and -10° C (23° and 14° F) when bases are warmer than about 10° C.
Anybody still out there?
So, yesterday, with the deepest Cumulus clouds around 2,000 to three thousand feet thick right in our area (they were deeper elsewhere), tops were running around -15° C, this temperature, as you know, leads to the formation of plate-like crystals, hexagonal plates, stellars (Christmas card crystals), maybe some spatial dendrites (stick out in different directions) if the latter crystals were in the Cumulus cloud long enough. If the concentrations of ice get high enough, you’ll get “snowflakes”, interlocking dendritic crystals. A single, good-sized snowflake might have 20-50 individual dendritic crystals.
Is anybody still out there?
Below some shots from yesterday afternoon when there were traces of ice spewing out of local clouds. Did you see those regions and note them in your cloud diaries, that’s the important question.
3:23 PM. A nice view of the overall scene around here with our small Cumulus clouds (Cumulus humilis and mediocris). You see a house in the distance off this dirt road. Pretty say when you think that in America some people still live on dirt roads.3:49 PM. Oh, there’s a nice little Cumulus toward the Charoleau Gap. Doesn’t seem to have any ice…. Let us look closer, and, of course, we look for ice to appear at the downwind edge where cloudy air has been in the cloud the longest, see if anything is falling out.3:49 PM zoomed view. Oops there it is, a little ice, single crystals, concentrations likely lower than 1 per liter of air. You wouldn’t expect to find any “aggregates” here, since they require higher concentrations of ice to bump into each other and lock together. Wow, this is an incredible amount information based on a little hazy spot in a photograph!4:13 PM. Lets look over here toward the south. OK, there’s an obvious ice haze beyond the Catalinas, but what about the cloud in the middle? See anything coming out the downwind (right) side?4:13 PM zoomed view of the fall of ice crystals out of this cloud. This patch of ice haze is so obvious it would have been pretty embarrassing for you not to have noticed it, made a note about it. Of course, we care so much about ice because that’s where nearly all of our rain here in Arizony comes from, as you know, recalling the work of Wegner, Bergeron, and Findeisen, where it was shown that an ice particle in a water cloud will grow at the expense of the droplets around it. For a time, it was thought that all precip of consequence was due to that process, but not so. Ask Hawaiians. Or powder snow lovers about storms consisting only of little dry ice crystals, no water drops in those clouds.
Stormy weather still ahead as noted here I don’t know how long ago. April looking more and more to be a generous month of rain here in Catalina. But will those showers be too late for May flowers?
We’ll have to suffer through a few days for the next storm, i. e., experience sunny weather with pleasant temperatures. Its amazing that people all over America come to Tucson to experience sunny days with pleasant temperatures!
0.45 inches total in The Heights of Catalina in this latest round of rain, sounds of rain. Actually, there was also some tiny graupel/soft hail in the rain yesterday, too.
Graupel indicates a lot of cloud droplet water overhead, and that ice crystals were colliding with them until they lost their identity and became little snowballs. In regions where there are very few ice crystals, graupel and the harder version, hail often form. Its likely that nearly all those rain drops that came down with the little baby graupel were melted graupels.
Graupels….. Makes me think of that rock group, Led Graupelin, didn’t have the impact of Led Zepelin. But I have LG’s one and only album entitled, “Compare to Led Zepelin.” Was only $2.99, too! Where’s my guitar? I think I will play, “Stairwell to Heaven” now…
When graupel or hail occur, there’s a pretty good electric charge up there in those Cumulonimbus clouds. Its best to be indoors when its hailing until you know if a strike might occur (if there hasn’t been one already). Besides, its not comfortable being out in hail. And if you were listening to the rain, you heard a few blasts of thunder toward Lemmon around 2 PM that came out of one of the more enthusiastic Cumulonimbus clouds that went by. Got 0.12 inches total to add to the night before’s rain of 0.33 inches.
Yesterday in clouds; a sojourn in clouds from morning to evening, in that order with no times noted
I know how much you like to see pictures of rain, so here’s one. You’re not like the “others” are you those people around you every day?
Then the piston of atmospheric subsidence slammed down to squash our Cumulus cloud tops to levels and temperatures where ice could not form….
Two picures in a row of a NWS-style rain gauge. Probably has never been done before. Has been getting a workout lately. Everyone should have one.
The weather ahead
Kind of funny to see the Canadian GEM model internally plagiarize itself. Compare last night’s panel at 500 millibars (below) with that same level’s panel foretold for six days from now.
Yep, its the same thing over again in six days, though with less rain IMO:
In another interesting model development, the best USA model, the WRF-GFS is having an internal CONFLICT of major proportions. Check these progs out generated by data only six hours apart. The first one, showing a big trough coming into Cal, was generated by global data taken at 5 PM AST last evening. The panel below it was generated by the same model based on global data taken just six hours later, at 11 PM AST (so it the most recent WRF output available) and has a big ridge along the California coast.
Valid at 5 PM AST November 20th.
“Which one will the fountain choose?”, to quote old song lyrics1:
Looks like CMP is low AGAIN on his prediction! Thought a third was the most that could fall in our present storm chapter (10% chance of more, that is), and best estimate, 0.165 inches. Now it looks like met friend and professor at a major university will be much closer with his half an inch prediction. Very painful. Kind of like Stanford with their brainy team beating the Washington Huskies in fubball . It really hurts.
Let us begin today with a look at desert grasses from this summer and falls rains. Pretty deep, knee high in some areas, but as we know here, full of nettles. Kind of a cool look though.
7:53 AM.
Was heading out to see, what from Google Space, appeared to be a new meteor crater near me, one maybe the astro boys missed. Turned out it was just a house under construction, pretty much underground as well. Kind of a cool thought to build like this, lots of energy saved, which is always good. Cell phone service likely compromised.
8:11 AM. An example of an earth house under construction here in the Catalina area.
Yesterday’s clouds
…and a dense discussion of detecting ice in them. I am hoping that my followers noted the time of the first appearance of ice in those Cumulus and Stratocumulus clouds that began to fill in during the middle and late afternoon. As that happened, a few raindrops sputtered down here just after 3 PM as that happened. You should have logged both these events, the first visual appearance of ice, and when those drops fell in your weather diaries.
The whole point of this blog is the detection of ice in clouds by layman and laywomen, or “laypersons” I guess it should be now days. This is because if you see ice developing in lower clouds, something will be falling out of them soon. Ice grows in water clouds at below freezing temperatures at the expense of droplets. Therefore, if they stay in a water cloud long enough, they will get heavy enough to fall out. Poor droppies disappear, unless the air is really rising fast.
An interesting side note is that the air FLOWS THROUGH clouds, exiting on the downwind side. A cloud does not just float along as is. It is moving slower than the air, even itty bitty Cumulus clouds the cloudy air is being replaced constantly. The cloud is really moving upwind relative to the air! The POSITION of the cloud moves downwind, but SLOWER than the air that goes into it.
However, if ice crystals form in a small cloud then, they will fall out as single crystals at the downwind edge; they are not going to reach the ground unless you’re on a mountain top. You saw a fair amount of ice exiting the downwind end of clouds yesterday, falling out and evaporating in the dry air there. Where the cloud is wide, then they can gain some mass, collide with droplets, or other crystals and fall to the ground.
2:38 PM. No ice nowhere. Windy conditions not shown.2:38 PM. Cumulus and Stratocumulus clustering to the south-southwest of Catalina, but no sign of ice.
You need clusters of crystals locked together, called “aggregates” or ones that have gone through riming, collisions of ice crystals with drops at below freezing temperatures that freeze on the ice crystal making it more massive to get rain drops to the ground. Riming is what leads to graupel (soft hail) and hard hail (the latter to crystals impacting larger, often precipitation-sized drops that freeze on them).
For air travelers, or those who examine tree icing after storms, rime ice is white and produced by small cloud drops; clear icing is caused by much larger drops, usually drizzle or rain drop sizes. If the drops are too small (much less than about 20 microns) they are too small to hit anything and rather go around solid objects. Let’s say you’re on the top of Ms Mt Lemmon, say at 8.000 feet in the fog. The temperature is 24° F. Its windy. You look around and you see no icing on the pine trees trees up.
Where are you?
Ans: at cloud base.
That’s because itty-bitty drops, too small to hit on pine tree needles are flowing around the needles. Some great comments to make that would enhance your stature as a cloud maven junior is to offer your companion the information, “Wow, look at those trees! Here we are ing the freezing fog, and yet they have no ice sticking to them! That means the cloud droplets are pretty small, smaller than about 20 microns! I guess we’re at the base of this cloud system above us.”
These would be really great things for you to say. Of course, as you drove up to Mt. Lemmon, you would know already how far above cloud base you are, but, what the HECK.
You’re at Ms. Mt. Lemmon again, You like it up there when its in the fog. This time the temperature is 25 ° F. Its windy. The pine trees are loaded with rime icing, the ice juts out in the direction from which the wind is coming.
Where are you?
Answer: At LEAST a few hundred feet, more likely a thousand feet or more above cloud base. Drops have reached sizes above 20 microns in size, as they usually do at these heights above cloud base in old Azy. Later, you notice that the clouds are topping Sam (Samaniego) Ridge at the 6500 foot level. Now, they can’t be disconnected layer clouds, but rather SOLID from base to where you are. Drops are tiny again at the bottom of each layer.
Here’s another example. You get up in the morning after a cold winter storm to see “iced trees” on Ms Lemmon. Another comment you could be making is that, “Wow (always begin with “wow”), those clouds must have really been low based last night, way down on Sam Ridge!”
Riming on trees is analogous to the collection of fog droplets by trees and vegetation along the west coasts of the continents in onshore moving banks of Stratus and Stratocumulus clouds that intercept hillsides. These can be significant sources of water. Some studies of droplet collections by trees have found that under the tree, something like 20-40 inches of “rain” can be collected by a tree in northern California.
Wow, I can’t believe all the information I am providing today! Its really incredible.
OK, to first visible ice yesterday, 3 PM:and
3:00 PM. FIrst ice begins to eject out the end of that Stratocumulus complex upwind of Catalina. When the body of the cloud began to be overhead, a few drops reached the ground!3:00 PM. Close up of ice ejecting out the downwind end of this Stratocumulus complex (that hazy stuff).3:30 PM. Classic example illustrating the air flow through a cloud that’s producing a little ice. What kind of ice? Looks like colder crystal types, plates, stellars, maybe some dendrites; defintely not warm crystal types like needles and hollow columns that form at temperatures above -10° C.4:49 PM. Nice lighting.5:21 PM. Wind shift clouds, those lowest ones on the horizon, begin to appear to the north-northwest horizon, toward Casa Grande.5:31 PM. The sun going down amid Cumulus or could be called, Stratocumulus castellanus.5:32 PM. OCNL LTG DSNT NNW at this time. Again you see those wind shift, frontal passage type clouds here. A wind shift to the NW didn’t hit here until about 1:30 am when the rains and temperature drop hit.
Range of amounts in Catalina, given kind of a marginal moisture situation:
Goose egg to 0.33 inches max, median 0.165 inches, CMP’s best forecast. A friend and met man/prof predicts 0.50 inches here, FYI.
Looking backward
Have felt a little guilty not posting cloud photos from the last storm, Oct 30th, leading my reader into some sadness, maybe even despair the following day when she didn’t see her cloud day reprised. Here are a couple of the characteristic scenes from that day, which includes a shot of a rare drizzling cloud. You will love that shot! Also reprised here is the pioneering technique of novella-sized captions.
8:07 AM. Note how the deteriorating Equestrian Road draws your eye to the bank of Stratocumulus. Quite artistic I think. Think of Bob Dylan’s mournful line, “If today was not an endless highway…1.” Equestrian Trail Road actually ends in Sutherland Heights., just so you don’t lose focus here.8:59 AM. The easy to read sign of a wind shift, one that pushed up the tops of the innocuous Stratocumulus to a thickness where drizzle drops began to form.
9:12 AM: “Drizzle, der it is”, as might be phrased in old TEEVEE show, In Living Color. Shape of lower cloud tells you that the wind is blowing from right to left.10:33 AM. Let’s quote Bob Dylan again, this time in one of his most famous incomprehensible songs, Subterranean Homesick Blues: “You don’t need a weatherman to know which way the wind blows; a horse will do.” Well, CMP added those last few words. Bob couldn’t think of something as good as that. The clouds and horse tell you the wind is blowing from right to left. Btw, ome people were so amazed by the words in that Dylan song quoted above that they began to call themselves, “Weathermen.” How crazy was that? Who in the WORLD would want to call himself a “weatherman” that wasn’t one?
1043 AM. The perfect Cumulus congestus? I think so.4:11 PM. Rainbow. Indicates raindrops are falling over there.
4:37 PM. Just pretty, no words needed.
Still windy outside, 6:03 AM to be exact. Looks like the observation of windy is going to be correct. Expecting some nice lenticular clouds to show up today. Have cameras ready. No rain before 7:15 PM. Overnight, watch out!
This was amazing. I approach one of the puddles on Equestrian Trail. I see that its raining HARD in the puddle. I am only 20 feet from it, but its not raining on my car! Here’s what that scene looked like:
3:26 PM. Equestrian Trail road puddle outbound from Sutherland Heights.
How could this be? Of course, we’ve all seen heavy rain on the road and drove into it. But the illusion here that was so striking is that it only SEEMED to be raining in the puddle, not around it since the drop splashes were not obvious as I drove up to it.
The rest of yesterday was pretty great, too, lots of rainbows, brilliant clouds and skies, too photogenic for a neurotic-compulsive photographer. However, one of 221 photos was of a human, a neighbor, not of clouds and rain shafts.
Here are a few too many cloud photos; excess is kind of a specialty of mine:
6:25 AM.6:25 AM.
6:25 AM. Unloading.6:26 AM.
7:40 AM.11:58 AM. Cumulonimbus cloud boils upward upwind of Catalina.12:25 PM. Getting closer….12:51 PM. Lightning strikes not that close…Hail up to pea size, though.1:10 PM. Backside of storm looked pretty good, too, quite firm and protuberant, indicating updraft still intact. Note whitish fallstreak, likely graupel and or hail.1:10 PM. Horse exults over extra rain.1:43 PM. Crepuscular rays due to rain, not haze. A pretty scene sez me.2:18 PM. Another dramatic scene.2:36 PM. Biosphere 2 hit by light rainbow.2:42 PM. For the sharp-eyed, bit of arcus cloud below Cumulus bases shows the northwest wind and cold front about to hit Catalina. Hit over there by Marana first. Was minutes away here.2:46 PM. Something akin to an arcus cloud is just about on Catalina. Remember, the shift of the wind precedes the cloud, and lifts the air above it. Did you notice how the whole sky began to fill in with clouds as the windshift hit and for the hours after that? Pretty cool, huh?3:56 PM. Awful dark out for this time of day. And yet another rainbow! Is this Hawaii, or WHAT? Rainbow colors end where snow is falling, not rain.
4:05 PM. Day closes with more storms drifting toward Catalina.
Lightly looking ahead
Still a lot of “troughy” weather ahead, and chance for decent November rains in the first half of the month after cold one goes by, followed by a short dry spell.
Truly LATE breaking news, untimely really, but Augustober 18th was too special a day to ignore:
Giant clouds, dense rain shafts, frequent lightning in the area throughout the afternoon, dewpoints in the high 50s to 60 F; can it really be after the middle of October? Or, is this some kind of preview of climate change we can look forward to in the decades ahead, that is, if you’re thunderphilic?
5:05 PM. An amazing scene, and thunderstorm with such powerful updrafts that when those updrafts are blocked by the inversion at the base of the Stratosphere, they force the winds at that level to slow or backup and the anvil protrudes upwind (center left), something that is common with severe thunderstorms. This was significant here because the winds at 40,000 feet were around 50 kts, far stronger than anything we have here during a typical summer rain season. Summer Cumulonimbus cloud anvils can splash outward easily against weak winds up there in summer when they hit that barrier at the top of the tropopause. This just in from Mark A: severe thunderstorms, I have just learned here on the 20th , were observed in the PHX, and the NWS has a great link going describing all the mayhem it produced. I did not know this until just now in the middle of writing this first caption when I read Mark’s e-mail.1:40 PM.
1:56 PM. Anvil of the Cumulonimbus over west Tucson, drifts overhead of Catalina, and in three minutes, rain drops started to hit the ground. This is amazing because those drops had to fall from at around 20, 000 feet above the ground (estimated as bottom height of this thick anvil) and could only have happened if those isolated drops had been hailstones ejected out the anvil, something that also only occurs with severe storms with very strong updrafts in them. So, if you saw those few drops fall between 2 and 2:05 PM you saw something pretty special.
6:26 AM. Early portent: Cu congestus, aka, “heavy Cumulus) piling up this early.6:29 AM. Mammatus of the morning., an extraordinary scene for mid-October, pointing to the possibility of an unusual day ahead with strong storms. as was the scientific basis for giant clouds on the 18th in the amount of CAPE predicted, over 1,000 units of Convective Available Potential Energy, later that day from computer models. That is a lot for mid-October, take my word for it.3:45 PM. Strong storms did not form over or near the Catalinas yesterday, but they did get something. As you can see the top of this guy (Cumulonimbus calvus) is very subdued compared to the giants that formed elsewhere.5:53 PM. Peakaboo Cumulonimbus calvus top east of Mt. Lemmon provided a nice highlight after sunset. And to have convection like this going on this late was remarkable. Some heavy showers and a thunderstorm formed downwind of the Catalinas about this time,, too.5:51 PM. Pretty nice, summer-looking sunset that day, too.
The weather just ahead, and this might be it for precip for the rest of October
A nice-looking upper level trough is ejecting over us from the SW this morning but the computer model says its going to be a dry event. A second low center forms just about over us in the next day. AZ model doesn’t see much rain for us throughout these events, and rain doesn’t begin here until after dark today.
I think that is WRONG; bad model. Watch for some light showers this morning, then a break and rain overnight (which the models do predict). Due this quite bad model forecast, as seen from this keyboard, I feel must interject for the blog reader I have, an improved rain prediction for Catalina over that rendered by a computer model.
Feel like guesstimating a minimum of 0.25 inches between now and Thursday evening, max possible, 0.60 inches, so the median of those two, and maybe the best guestimate being the average of those two, or 0.425 inches here in Catalina. When you see a prediction of a rainfall total down to thousandths of an inch, you really know that the person predicting it knows what he is doing…..
Below, your U of AZ disappointing, but objective, take on the amount of rain based on last evening’s data and one that is the result of billions of calculations. One must remember that cloud maven person’s calculation of the rainfall amount for Catalina is only based on three.
From the 5 PM AST run executed by the U of AZ Beowulf Cluster.
Rarely do passing lows get a two chances to produce rain, but the low passing overhead today and tomorrow, does. Ten days from now, its overhead again! How funny izzat? And precipful, too.
Measurable rain will fall today in Catalina CDP (“Census Designated Place”, i.e., its not a city), and in about 10 days when the SAME low returns after a boomerang trip down Texico way, thence to Baja, thence to so Cal, and back over Arizona on the 10th-11th after picking up some juice over the east Pac.
Thinking, as you are now, of a minimum of 0.05 inches and top of 0.50 inches, the latter larger amount if projected afternoon thunderstorms land on us. Thus, best estimate, average of those two extremes, thinking Gaussian conceptual model modal value here, about 0.275 inches.
BTW, should be something in the way of an arcus cloud, or a batch of low scudding clouds underneath Cumulus and Cumulonimbus bases this afternoon as a windshift to the NW comes through in the afternoon or early evening hours, well in the next 18 h or so. That could be a dramatic sight, and with that windshift, the temperature will drop 5-10° F.
When the low trudges over us the second time around in mid-October, the estimated extreme amounts are a trace minimum, and 1.00 inch max, in other words, pretty clueless here about how much could fall the second time around ten days from now.
If you don’t believe me about all this, here are is the WRF-GFS prediction for this afternoon, followed by the WRF-GFS model prediction 10 days from now, today being October 6th, in case you don’t know what the date is today, maybe you’re retired and lose track of the days and dates because you don’t have a lot to do everyday, just kind of sit there:
5 PM AST, today, October 6th. Joe low goes by, heads toward Texas.5 AM AST, Friday, October 16th, the day before football day. Joe returns after visiting NM, TX, MEX, Baja, east Pac, then SC. Full cycle here, from IPS MeteoStar. Pretty humorous to watch this happen.
Yesterday’s clouds, punctuated by a large worm
6:57 AM. If you thought the clouds were fatter to the north most of the day yesterday, you were right. Many modest Cumulus passed overhead of Catalina and then fattened up to the north because the lifting mechanism aloft was stronger to the north of us. Quite a few moiuntainstations registered over an inch to the north of us.
However for a moment, we did have a shower threat move toward us from the south, this:
11:52 AM. Whilst on a hike up the Baby Jesus Trail, this appeared. Looked promising! But, vaporized into mere sprinkles. If you saw this, you almost immediately were thinking of ice forms like needles and sheaths, since the cloud was relatively shallow, and its still warm aloft. Needles and sheath (hollow columns) only form at temperatures above -10° C. Such an occurrence is rare in Arizona, so, quite an interesting bit of hand-waving here.10:57 AM. Hike up the Baby Jesus Trail was punctuated by seeing a very colorful worm of some kind. Not much else happened in weather or wildlife the rest of the way, Morning glory coverage was a little disappointing.4:17 PM. I am sure when you saw this Cumulus congestus that you, as I was, thinking you’d see a little ice emit out the right, aging and descending side of this cloud. In fact, no ice was visible. However, it was kind of neat to think how close we are now days in our cloud assessments, right or wrong.
