Category Archives: Nimbostratus

Hawaii comes to Arizona from Mexico; 5.91 inches at Dan Saddle! 6.43 inches on Mt. Graham!

Former Hurricane ‘Newt’ brought some real humidity, low clouds with unusually warm bases (around 15-20 ° C) to Tucson and Catalina yesterday as its remnant center passed just about over us.

Old Newt was “dragging” here as a tropical storm, aloft it was pretty strong still,  brought near hurricane force winds on isolated, high, mountain tops.  Mt. Hopkins reached 59 kts from the ESE before the “eye” passed nearby  and the winds turned to the west.  And in the Rincon Mountains   a gigantic 6.39 inches was logged, and a site on Mt. Graham reported 6.43 inches.  (Thanks to Mark Albright for these reports.)

While Sutherland Heights received only 0.29 inches in that all day rain, there were eye-popping totals in the Catalinas.    Take a look at some of these, Dan Saddle near Oracle Ridge,  nearing 6 inches in 24 h!  Below, 24 h totals ending at 2 AM this morning, which pretty much covers Newt:

0.28 Golder Ranch Horseshoe Bend Rd in Saddlebrooke
0.59 Oracle Ranger Stati approximately 0.5 mi SW of Oracle
0.24 Dodge Tank Edwin Rd 1.3 mi E of Lago Del Oro Parkway
0.35 Cherry Spring approximately 1.5 mi W of Charouleau Gap
0.79 Pig Spring approximately 1.1 mi NE of Charouleau Gap
0.47 Cargodera Canyon NE corner of Catalina State Park
0.31 CDO @ Rancho Solano Cañada Del Oro Wash NE of Saddlebrooke
0.39 CDO @ Golder Rd Cañada Del Oro Wash at Golder Ranch Rd
4.13 Oracle Ridge Oracle Ridge, approximately 1.5 mi N of Rice Peak
4.25 Mt. Lemmon Mount Lemmon
1.61 CDO @ Coronado Camp Cañada Del Oro Wash 0.3 mi S of Coronado Camp
2.17 Samaniego Peak Samaniego Peak on Samaniego Ridge
5.91 Dan Saddle Dan Saddle on Oracle Ridge
3.54 White Tail Catalina Hwy 0.8 mi W of Palisade Ranger Station
3.66 Green Mountain Green Mountain
1.77 Marshall Gulch Sabino Creek 0.6 mi SSE of Marshall Gulch

Your cloud day yesterday; we don’t talk about today.  That’s for tomorrow.

The day began with one of the great examples of Nimbostratus, that technically a middle -level cloud greeted us at daybreak in what was one of the great examples of the phantom cloud, the true precipitator, usually hidden from view by lower clouds such as Stratocumulus.  But, yesterday morning, there it was,  “Ns” naked as could be.  I know many of you have been looking for a good shot of Nimbostratus to add to your cloud collection for a long time and I could feel the joy out there when I saw it myself.   I only took a couple of shots myself, wish now I had taken more of an extraordinary scene.

6:49 AM. Nimbostratus! Note how high the bottom is, a bottom marked mostly by falling precip, usually snow because steady light rain is so relatively transparent.
6:49 AM. Nimbostratus! Note how high the bottom is, a bottom marked mostly by falling precip, usually snow because steady light rain is so relatively transparent.
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6:52 AM. Looking NNW toward parts of Saddlebrook/Eagle Crest developments. Notice the nice, relatively uniform, blurry gray, the “blurry” look due to falling rain, the perceived bottom, at the melting level, snow is melting into rain. In winter, therefore, the “bottom” or base of Ns, absent lower clouds, appears lower to us because the snow level is lower.

Then, as the light rain here moistened the air hour after hour, low clouds, such as Stratocumulus and Stratus fractus began to form along the mountains, producing some interesting “tracers” of the chaotic air movement over there by the Catalinas under nearly calm conditions.  Newt disappointed in his wind accompaniment.

1:41 PM. Stratus fractus clouds lined Samaniego Ridge, Stratocumulus or weak Cumulus topped it, with a higher layer of Stratocumulus above that.
1:41 PM. Stratus fractus clouds lined Samaniego Ridge, Stratocumulus or weak Cumulus topped it, with a higher layer of Stratocumulus above that,  That highest layer was once the much deeper Nimbostratus, but now has lost its deep part, so its no longer “Ns” since its not precipitating.
1:42 PM. The deep stratocast has departed, the remaining clouds in the foreground are Stratocumulus. The darkening bases on the horizon southwest of Pusch Ridge are where Cumulus and Cumulonimbus clouds filled with rain are piling up, likely due to the light winds coming together down there, maybe in the low center that was once "Newt."
1:42 PM. The deep stratocast has departed, the remaining clouds in the foreground are Stratocumulus. The darkening bases on the horizon southwest of Pusch Ridge are where Cumulus and Cumulonimbus clouds filled with rain are piling up, likely due to the light winds coming together down there, maybe in the low center that was once “Newt.”

 

Later in the day, as the highest, coldest cloud tops associated with those beautiful Nimbostatus clouds moved off to the NE, and our cloudscape became a mix of deeper Stratocumulus with Cumulus and isolated Cumulonimbus cells,  they produced true drizzle and misty, visibility-reducing “warm rain”, that rare type of rain that falls here from clouds lacking in ice, began to be observed producing Hawaiian looking rain on our mountains, delicate shafts of rain whose small drops slanted away from the base.

2:32 PM. Misty drizzle and very light rain! When did this transition happen?
2:32 PM. Misty drizzle and very light rain! When did this transition happen?
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2:32 PM. Hard to tell the difference here in a photo between the pure, naked Ns, and this lower drizzle,misty rain producing cloud likely topping out well below the freezing level. I’ve seen these transitions before, but I missed this one, where a Stratocumulus deck starts to look a little fuzzy on the bottom as the drizzle, very light rain starts to come out (due to tops rising, drops at the top getting larger, at some point crossing over the “Hocking” droplet threshold of larger than about 38 microns in diameter, where they begin sticking together when they hit). Here, the transition from non-precipitating Stratocu to I-don’t know what has already taken place during between the photos at 1:41 and 1:42 PM. Should drizzly, relatively shallow clouds like these now be termed, Nimbostratus? Or Stratocumulus praecipitatio,to emphasis the shallowness? A question definitely for the cloud philosophers to haggle about. No member of the cloud maven club would be punished for calling this scene one showing “Nimbostratus.” However, the drizzle and very light misty rain should have told you it was from a far different cloud structure than that associated with true Nimbostratus, always a deep cloud with ice in it, often topping out at Cirrus levels.

Here, you might well erupt with, “This doesn’t look like Hawaii, but Ocean Shores, Washington, or some other coastal location along the West Coast on a spring day having Stratocumulus with drizzle!”

You would be correct in that eruption.

Below, an example of drizzle drops on your car’s windshield:

3:50 PM. The tiniest drops you can make out on the window are drizzle drops.
3:50 PM. The tiniest drops you can make out on the window are drizzle drops.  I focused on them and you’ll have to click on it to get the full size to be able to see them.  I was so excited to see some more of them!

Later, it was to look little more “Hawaiian”, but if you’ve been to Hilo, you know its mostly cloudy all day.

 

“Warm rain” or rain due to the colllision-coalescence process, is also mainly associated with “clean” conditions, ones low in aerosol particles that can act as cloud condensation nuclei.  The fewer the “CCN” the fewer are the droplets in clouds, and the larger the individual cloud droplets are when saturation and cloud formation occur.    So, by yesterday afternoon, certainly, it was doggone clean here, no doubt aided by washout in that light rain we had.

 

 

Particularly heavy rain with low visibility fell just south of Catalina yesterday afternoon around Ina and Oracle just after 4 pm.  However, that rain did not have those HUGE drops that we see from unloading, deep, Cumulonimbus clouds making this observer think as heavy as it was, it may have been due to a Cumulonimbus topping out at less than 20,000 feet, where the temperature would have been too warm for ice.  The 500 mb temperature yesterday was a tropical-like -3.7° C on the TUS sounding, almost unheard of with a rain situation here.  This, another sign of tropical Newt, since tropical storms/hurricanes have warm cores.

lacking in those huge drops we see in our thunderstorms, this rain likely formed from the “warm rain” process except maybe in the very heaviest rain areas.  It was a special day.

You probably noticed how quiet it was; no thunder around, for one thing, indicating the updrafts in the clouds were not very strong, and that was another indicator that the clouds may not have contained ice.  Without ice, hail and graupel, soft hail, you don’t have lightning.

The lack of lighting, the all day off and on rain, such as you might experience at Hilo, Hawaii, on the windward side, made it seem like you were in Hilo, Hawaii, or one of the other wet spots on the windward side of the Island.

3:27 PM. Another, to me remarkable misty scene reminiscent of oceanic and coastal Stratocumulus with drizzle and light rain
3:27 PM. Another, to me remarkable misty scene reminiscent of oceanic and coastal Stratocumulus with drizzle and light rain
3:52 PM. In the meantime a much deeper cell had developed to the SW of us, down around Ina and Oracle, where an inch and a half of rain fell. Look how the bottom is so close to the ground, like at a temperature near 20° C, about as warm as a cloud base can be here! And the warmer the base, the more water is going up into that cloud! Very exciting scene! Well, they all are to people of cloud maven persuasion.
3:52 PM. In the meantime a much deeper cell had developed to the SW of us, down around Ina and Oracle, where an inch and a half of rain fell. Look how the bottom is so close to the ground, like at a temperature near 20° C, about as warm as a cloud base can be here! And the warmer the base, the more water is going up into that cloud! Very exciting scene! Well, they all are to people of cloud maven persuasion.
4:24 PM. Into the bursting cloud. Still, drops were not HUGE, as you would expect, but extremely numerous, rain rate over an inch an hour in the heaviest parts. Was taken I around Oracle and McGee, and of course, not while driving. That would be crazy. Only looks like it.
4:24 PM. Into the bursting cloud. Still, drops were not HUGE, as you would expect, but extremely numerous, rain rate over an inch an hour in the heaviest parts. Was taken I around Oracle and McGee, and of course, not while driving. That would be crazy. Only looks like it.
6:32 PM. One of the more Hawaiian looking scenes, fine trails of rain dragging along the Catalina Mountains. The slope of the rain coming out absent much wind down low tells you the drops are small, probably near drizzle sizes. And the "shaft" if you will, is diffuse, indicating the small drops are spreading out due to the little turbulence there was making it fuzzy around the edges.
6:32 PM. One of the more Hawaiian looking scenes, fine trails of rain dragging along the Catalina Mountains. The slope of the rain coming out absent much wind down low tells you the drops are small, probably near drizzle sizes. And the “shaft” if you will, is diffuse, indicating the small drops are spreading out due to the little turbulence there was making it fuzzy around the edges.  Maybe, anyway.

Quitting here.

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Traces of rain and a Lemmon rainbow

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6:25 AM. Altocumulus perlucidus. According to my cloud chart, informally known as “America’s Cloud Chart”, it could rain within 6 to 196 hours. Its quite useful.
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10:24 AM. Altocumulus opacus. Note the rumpled look of the sky. Indicates that the clouds are rather shallow and composed of droplets rather than a mix of ice crystals and droplets. However, if you strain your eyeballs and look to the horizon, you can see a smoothing and a little virga showing that the cloud tops are rising and they’ve gotten cold enough to produce ice. According to my cloud chart, when you see “Ac opacus” it could rain within 6 to 196 hours.
DSC_0622
1:44 PM. While the clouds are pretty much the same gray color as in the prior photo, they’re much thicker here and are “Altostratus opacus”. “opacus” because the sun’s position is not visible, though it wouldn’t be in this direction anyway, but to the right. The bottom of this is smooth due to widespread, light falling snow, though it not in a localized area enough to be called virga in this shot. The lack of bunched or heavy virga somewhere tells you that the cloud tops are pretty smooth, too, not a lot of variation in height.  The base is really determined by the point that you descend out of this precip, in this case up around 10 kft above the ground over Catalina.
4:12 PM.  Altostratus opacus praecipitatio or Nimbostratus, either name will do.  Recall the quirk in our cloud naming system that makes, "Nimbostratus" a middle-level cloud.  The base of these clouds is the general level where the snow falling out has evaporated.  Due to bulging tops, and stronger updrafts, a little of the precip was able to fall out because the snowflakes coming out the bottom had grown larger and were able to survive the dry air below cloud base.
4:12 PM. Altostratus opacus praecipitatio or Nimbostratus, either name will do. Recall the quirk in our cloud naming system that makes, “Nimbostratus” a middle-level cloud. The base of these clouds is the general level where the snow falling out has evaporated. Due to bulging tops, and stronger updrafts, a little of the precip was able to fall out because the snowflakes coming out the bottom had grown larger and were able to survive the dry air below cloud base.

Some rain fell about this time in Catalina.  Not enough to darken the pavement completely at any time.  The main thing to take away from that hour of very light rain is that it was not “drizzle” as even some errant meteorologists call such sprinkles.

You will be permanently banned from attending any future meetings of the cloud maven club if you refer to such rain as we had yesterday afternoon as “drizzle.”  Drizzle is fine (200-500 micron in diameter drops that are very close together and practically float in the air.  Because they fall so slowly, and are so small to begin with, you can’t have drizzle at the ground from clouds that are much more than a 1000 feet or so above the ground because as soon as they pop out the bottom, those drops start evaporating and fall slower and slower by the second, and in no time they can be gone even in moist conditions.  That’ s why its somewhat hilarious and sad at the same time,  when, in particular, military sites for some unknown reason, report ersatz “drizzle: (coded as L, or L-) in our hourly aviation reports from clouds that are based at 5000 feet or something CRAZY like that.

This band of Nimbostratus/Altostratus had a backside that approached as the sun went down, and as you know, that clearing let some sunlight enrich and dramatize the views of our beloved Catalina Mountains:

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5:39 PM.
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5:41 PM.

Finally, dessert:

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5:47 PM. Rainbow lands on the University of Arizona Wildcat’s Skycenter atop Ms. Mt. Sara Lemmon.
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5:48 PM.

The amazing rains ahead

Nothing that you don’t already know about, so no use me blabbing about it too much.  But in case you haven’t seen it, The Return of Joe Low (after over-hydrating over the warm waters of the eastern Pacific), is expected over the next couple of days, with a little help from another disturbance, to bring colossal rains to eastern Arizona and especially New Mexico.

Below, from our friendly U of  A Wildcat Weather Department a model run from yesterday’s 5 PM global data (the Wildcat’s downsize the US WRF-GFS model in this awesome depiction).

Check out the totals expected by the evening of October 23 rd.  Stupendous.  Usually these totals are a bit overdone, but even so…… Will take a nice bite out of drought.

Precipitation totals expected by 5 PM AST October 23rd.  Looks something like a tie-dyed Tee.
Precipitation totals expected by 5 PM AST October 23rd. Looks something like a tie-dyed Tee.

The End

So happy for you

For the second time this month, cloud-centric folk had a rare and happy sight:  “naked” Nimbostratus, that is, the well-known mid-level1 precipitating cloud layer was present for all to see, but without the obscuring lower cloud decks normally associated with it, clouds like Stratocumulus or Stratus.  Time and time again those pesky lower layers  prevent one from seeing whose really producing the rain or snow at the ground because when precip is falling, its normally moist enough that lower clouds are present.

Those lower layers are important in enhancing precip because while they aren’t precipitating themselves (though it may seem like it) the drops falling into them from the Nimbostratus higher up,  1) won’t evaporate inside the cloud, and 2),  if the droplets in the Stratocu are large enough, some of them will be collected by the raindrop falling through it and it becomes larger, the rain that bit heavier!  How great is that?

Its really hard to compare how rare yesterday’s  sight of “naked” Nimbostratus was yesterday, but offhand, I would say its about as rare as a professional wildlife photographer2 catching a shot of  Cockrum’s Gray Shrew, aka,  the “Hairy Packrat” or just “Harry Packrat”,  shown below:Desert-Shrew-or-Cockrum's-Gray-Shrew-0002[2]

Oh, yeah, that Nimbostratus layer sans lower clouds….

12:37 PM.   A layer of pure Nimbostratus produces very light, steady rain in Catalina.
12:37 PM. A layer of pure Nimbostratus produces very light, steady rain in Catalina.  Cumulostratus3 clouds line the Catalinas below it.

Except for the rarity of the view, not much to see.  The bottom is blurred by falling precip, and when its snow, where that snow melts into rain is perceived as the base of Nimbostratus.  So…….in the warmer time of the year, “naked” Nimbostratus has a higher perceived “base” than in the cooler time of the year.

There was also another unusual situation, a cloud layer that really has no good name which I will now call from here on, “Cumulostratus.”  See below:

12:07 PM.  A great example of the newly named cloud, "Cumulostratus."  Really there is no existing name that really hits this, maybe Stratocumulus castellanus.
12:07 PM. An example of the newly named cloud, “Cumulostratus.” Really there is no existing name that really hits this, maybe Stratocumulus castellanus.

2:07 PM.  Kind of fun to see the hide and seek the clouds were playing with Samaniego Ridge and Ms Mt Lemmon, too.
2:07 PM. Kind of fun to see the hide and seek the “Cumulostratus” clouds were playing with Samaniego Ridge and Ms Mt Lemmon, too.

Not much immediately ahead in weather, oh, maybe some scattered showers later Sunday through Tuesday.  Nothing really great jumps out of the spaghetti plots in the longer term.

The Canadian model thinks the newly formed  desert lands of northern Cal all the way down to “Frisco” will get drenched, beginning in five days or so.   That’s good.  The USA model, using  the same global obs at 5 PM AST yesterday, do not see that happening, but rather just some very light rains.  Go Canada!

The End

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1Probably doesn’t seem like Nimbostratus should be grouped with mid-level clouds like Altocumulus and Altostratus, but it is, strangely believe it, as I like to say.  On synoptic weather maps it was placed above the station circle, indicating a mid-level or high cloud was present,  as a “lazy F”, the character “F” lying on its back.  Cloud types are no longer plotted on surface weather maps since today, clouds are mostly detected by machines, not humans.  “Rise of the machines.”  You know the story.

2The shot here  forwarded to me with much excitement by pro photographer, Rick Bowers, of Bowers Photo,  who had tried to photograph this vermin for about 20 years he reported.

3“Cumulostratus” is a name I made up because IMO there really is no satisfactory name for the cloud that lined the Catalinas/Samaniego Ridge yesterday.