2185: Cumulonimbus

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The rarest of all clouds is the altocumulenticulostratonimbulocirruslenticulomammanoctilucent cloud, caused by an interaction between warm moist air, cool dry air, cold slippery air, cursed air, and a cloud of nanobots.
Title text: The rarest of all clouds is the altocumulenticulostratonimbulocirruslenticulomammanoctilucent cloud, caused by an interaction between warm moist air, cool dry air, cold slippery air, cursed air, and a cloud of nanobots.


This comic follows the naming of clouds. As with other lists (like in 2022: Sports Champions), it starts off as normal but then gets more unusual until it is unrealistic.

The first panel shows a cumulus cloud, from the Latin for "heap". These are common clouds and are relatively small. Cumulus clouds form when warm (and thus rising) moist air condenses when it hits the dew point, the temperature at which relative humidity hits 100%. Cumulus clouds with sharp, defined borders are still growing. When they stop growing (because the rising moist air is exhausted), they get fuzzy and fluffy, and eventually dissolve.
The second panel shows a cumulonimbus cloud, from the Latin for "heaping raincloud", with the upper part about the same size as the lower part. Though somewhat like the cumulus cloud, it is more prone to causing rain and lightning. Cumulonimbus clouds, like cumulus clouds, grow vertically because of their moist warm air, but they have enough energy to reach the top of the troposphere, giving them the distinctive anvil shape shown in the comic and their tendency to produce nasty weather.
The third panel shows an even bigger cloud and names it cumulonimbulonimbus (Latin for "heaping rainy raincloud"). Here the scientific facts end and the humor begins. The cloud has the upper part about twice as large as the lower part. The humor here comes from building up an even bigger name by adding another "nimbus" element for the cloud as its size increases, suggesting that its growth as compared to the second cloud shown has made it even more "rainy".
The fourth panel shows an absurdly large cloud with three major layers and gives it the name cumulonimbulonimbulocumulonimbus (Latin for "heaping rainy rainy heaping raincloud"). This is a combination of the third and second cloud names in this comic, and indeed the fourth cloud looks a lot like the second one emerging out of the top of the third. This cloud may look like a super soaker, ready to spray water on everyone, or perhaps a faucet ready to open and pour water down.
The title text takes this comic to its logical extreme by naming a new cloud that has the longest name of them all and is also supposedly the rarest. Its name can be translated as "mid-altitude, heaped, lense-shaped, layered, grey, rainy, wispy, breast-like and lit at night". It mentions a common joke in weather communities, making fun of the common trope that thunderstorms form when "warm moist air" meets "cold dry air," an extreme oversimplification. A complicated cloud needs complicated processes, so Randall adds in "cold slippery air," then cursed air and nanobots, which makes the cloud impossible since neither of those exist.[citation needed]
The name of this cloud is a compound of the following cloud names:
altocumulus: "heap up high"; these clouds are mid-altitude white patches.
lenticular cloud, often shaped like a flying saucer.
stratus: a layered cloud, effectively above-ground fog.
nimbus: a grey cloud producing continuous rain.
cirrus: a cloud that looks like thin, wispy strands.
"lenticulo" gets repeated, perhaps indicating that there's a second disc in the cloud.
mammatus: a breast-like cloud structure that forms at the bottom of some thunderstorm clouds, which signifies sinking air and is associated with severe storm activity and, in the central United States, tornado formation.
noctilucent: a cloud-like structure formed from ice crystals, often formed after volcano eruptions and other cataclysmic events and illuminated by a just-set sun.

The International Cloud Atlas defines the cloud types that are recognized by the WMO, the World Meteorological Organization. It was first published in 1896. Similarly, IUPAC publishes a manual that allows chemists to name chemical compounds in a consistent manner. The Altocumulenticulostratonimbulocirruslenticulomammanoctilucent may thus be a pun on IUPAC, which (theoretically) offers a unique name for each possible strand of DNA and other complex molecules (such as Titin). Therefore, Randall might have seen a unique cloud that has never been observed before, but yet, thanks to IUPAC-like cloud naming rules, he came up with a "valid" name for his observation.


[Drawing of a small cloud with with a label beneath:]
[Drawing of a medium sized tall hourglass shaped cloud with a label beneath:]
[Drawing of a large cloud, larger at the top than at the bottom, with a label beneath:]
[Drawing of a huge and very complicated cloud in three layers, with a label beneath:]


  • On xkcd, this comic replaced a preceding "disappearing comic", which temporarily was assigned the sequence number 2185, as it followed the Friday comic 2184: Unpopular Opinions already on Sunday. But that was just to prevent the trouble a not numbered comic was having on the xkcd site. It was designed to disappear completely and leave no trace in xkcd's history or archives when this comic was released. The original comic does also no longer appear in explain xkcd's comic navigation either, and is hence linked here: Disappearing Sunday Update.

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Hey, the back arrow here doesn't go back to yesterday's "Disappearing Sunday Update" 18:17, 5 August 2019 (UTC) That's why it was disappearing. 18:42, 5 August 2019 (UTC)

I think this could be improved by expanding out the translations from latin for the various parts of each cloud's name. I.e., cumulus is just "heaped"; cumulo-nimbus would be "heaped raincloud"; cumulo-nimbulo-nimbus would be "heaped rainy raincloud"; cumulo-nimbulo-nimbulo-cumulo-nimbus would be "heaped, rainy, rainy, heaped raincloud", and alto-cumu-lenticulo-strato-nimbulo-cirrus-lenticulo-mamma-noctilucent would be "mid-altitude, heaped, standing, rainy, wispy, standing, highly turbulent, and lit at night." (Some of these descriptors are contradictory; cirrus clouds can not also be mammatus clouds.) (And yes, "mammatus" clouds mean what you think they mean.) 19:08, 5 August 2019 (UTC)

It says "soaker" in the description of the fourth cloud. Do we mean "super soaker"? It does look like a super soaker. I didn't dare change the description in case I am missing something. Cow (talk) 20:15, 5 August 2019 (UTC)

It says "soaker" in the description of the fourth cloud. It should say "Super Soaker"! 11:27, 6 August 2019 (UTC)
I have corrected this with a link to 220. --Kynde (talk) 12:58, 6 August 2019 (UTC)

I added that is may also look like a faucet. See https://encrypted-tbn0.gstatic.com/images?q=tbn:ANd9GcQzDGZ1TMWwki03pJ9dbpJhaXeq2mVq3fcO1GeDfPhx_5BHMT7K. The little nub on the back top could represent the stopper control, and the little nub on the front could be the teat that holds the bucket handle. I couldn't find a picture of one with a little nub on the front to hold the bucket handle - maybe it's old fashioned and they don't make them like that anymore - but I distinctly remember then from my childhood. update: found one https://as1.ftcdn.net/jpg/01/44/45/98/500_F_144459810_nJ4eVcyNP0NWkEoXYFfHzvda2uEJXOhA.jpg

Could we modify the navigation system to go to the disappearing one? That's right, Jacky720 just signed this (talk | contribs) 20:21, 5 August 2019 (UTC)

No, the system should go through the comics as they are on xkcd. But there has been added trivia sections to both this and the previous comic with link to Disappearing Sunday Update. --Kynde (talk) 12:50, 6 August 2019 (UTC)
You an find this and other comics not part of the normal xkcd relase schedule here: Category:Extra comics --Kynde (talk) 12:58, 6 August 2019 (UTC)

The explanation for the fifth cloud splits noctilucent into noctus and lucent and saying they have nothing to do with clouds when its actually referring to a type of very high altitude cloud seen rarely around twilight/dusk. They form from ice crystals and are illuminated by the sun below the horizon. --Kirkerbot (talk) 23:31, 5 August 2019 (UTC)

The listed lapse rate for the troposphere seems high - the dry adiabatic lapse rate is around 9.8 °C/km, and Wikipedia indicates the average lapse rate is around 6.5 °C/km. Tovodeverett (talk) 05:02, 6 August 2019 (UTC)

We should add some more info on the cloud types that "Altocumulenticulostratonimbulocirruslenticulomammanoctilucent" seems to reference (altocumulus, stratus, cirrus etc.) Arcorann (talk) 11:01, 6 August 2019 (UTC)

I've added <wbr> tags to the long latin names, so they break at sensible places. If someone could verify that I've added them to the right places, that'd be great. Also, maybe we should/could use a soft hyphen (&shy;) instead? -- //gir.st/ (talk) 12:26, 6 August 2019 (UTC)

Can someone create a category for "Weather"? This is one of many comics about weather, but I don't have permissions to create the category. Natg19 (talk) 16:37, 6 August 2019 (UTC)

Maybe... See personal message about creating such a category. I have removed it until we find out if that category is relevant enough. Should it be called just "Weather"? --Kynde (talk) 07:21, 7 August 2019 (UTC)
After a minor discussion on Natg19's user page we have chosen to create the Category:Weather after all, and with this name. Please feel free to add comics about weather to it. This one has of course been added --Kynde (talk) 11:24, 9 August 2019 (UTC)
I feel like there have been plenty enough comics about weather to warrant such a category. And I DO find categories and groups work best when named / defined as simply as possible, to make it easier to select group members. :) "Weather" is a very yes or no name, either a comic is about weather or it isn't, nice and easy. NiceGuy1 (talk) 04:06, 15 August 2019 (UTC)

The last cloud does look like a supersoaker, but it also reminds me of something expanding fractally. 17:49, 6 August 2019 (UTC)

Whoever added the "citation needed" to the statement that cursed air does not exist has never gone in a bathroom after me.Daemonik (talk) 10:32, 7 August 2019 (UTC)

Anyone getting major OREREREREO vibes here?

Why was my addition that "The title text also mentions a common joke in weather communities, making fun of the common trope that thunderstorms form when "warm moist air", meets "cold dry air", which is an extreme oversimplification. An example of this trope is here. " removed? No explanation was given.

Maybe because you don't sign your comments? :) Seriously, maybe it was that you left in the unnecessary "feature" parameter in that YouTube link (you only really need the "v" parameter), or that you included the "t" parameter (jump to 448 seconds into the video) but didn't mean to? NiceGuy1 (talk) 04:06, 15 August 2019 (UTC)