Why NASA Still Asks People to Stand Outside and Name Clouds
How many clouds could you actually name before starting this cloud types quiz — three, maybe four? There are ten official ones, the number has not changed in living memory, and the reason that matters has nothing to do with trivia. NASA runs a program that asks ordinary people to stand outside, look up, and identify what they see, and it does that because there are things about clouds its satellites physically cannot determine from orbit.
Two Centuries On, There Are Still Exactly Ten
The World Meteorological Organization rebuilt the International Cloud Atlas in March 2017. It was the first revision since 1987 and the first edition published as a website rather than a book, and it was a genuinely large piece of work — a new species (volutus, the roll cloud), five new supplementary features, one new accessory cloud, and a whole vocabulary for clouds of human origin, so that a contrail is now formally cirrus homogenitus.
And the count of genera after all that? Ten. Exactly where it was before. That stability is the thing worth pausing on, because it is not conservatism. Luke Howard proposed the framework to the Askesian Society in December 1802, choosing cirrus for a curl of hair, cumulus for a heap, stratus for a layer and nimbus for rain, and publishing it the following year. He wrote in Latin specifically so the names would cross borders, which is exactly what happened — within a decade the system was in general use across Western Europe, helped along by Goethe, who admired it enough to write verse about it.
The system survived because Howard classified clouds by what a person on the ground can actually observe: how high the base sits and what form the cloud takes. Those two readings still separate all ten genera today, and they are the two readings the identification half of this quiz gives you for every sketch.
What an Orbiting Satellite Cannot See
Here is the part that surprises people. A weather satellite is extraordinary at measuring cloud tops, cloud temperature and coverage across an entire ocean basin. It is close to useless at two things: the height of a cloud's base, and the existence of any cloud sitting underneath another one. A satellite looks down and sees the topmost layer. A thin sheet of cirrus at nine kilometres will hide an entire stratocumulus deck beneath it, and from orbit that deck simply is not there.
Which is why NASA's GLOBE Clouds program exists. Volunteers photograph the sky and record what they see, and if the observation lands within 15 minutes of a satellite passing overhead, the two views get paired into what the program calls a data match — bottom-up and top-down, describing the same air at the same moment. The program passed one million of those matches. Every one of them contains something the satellite could not have supplied on its own.
That is a genuinely unusual position for a citizen science project. Most of them are about scale: many people doing a simple task that one lab could do slowly. This one is about a capability gap. The person in the garden is not a cheaper satellite — they are looking from a direction the satellite cannot occupy.
Every Identification Comes Down to Three Readings
A trained observer does not identify clouds by how they feel. They record three things, in order, and the genus falls out of the combination. The field note above each sketch in the cloud types quiz above gives you exactly those three, because that is the entire method — there is nothing else being withheld.
Base height splits the ten into families. Above roughly six kilometres you are in the high group and everything there is made of ice: cirrus, cirrocumulus, cirrostratus. Between two and seven kilometres is the middle group, marked by the alto- prefix. Below two kilometres sit stratus and stratocumulus. Cumulus and cumulonimbus break the scheme by having low bases and enormous vertical extent, which is why they are often grouped separately.
Formis Howard's original split, and it is really a question about the air rather than the cloud. Heaped, lumpy, sharply outlined clouds — the cumulo- forms — mean air is rising in discrete parcels. Flat, featureless sheets — the strato- forms — mean the air is stable and layered. That is the physical difference underneath the visual one.
Precipitation settles the remaining ambiguity. Only two genera reliably deliver rain to the ground, and they do it in opposite ways: nimbostratus produces steady rain for hours from a formless deep layer, and cumulonimbus produces something violent and brief from a single towering cell.
There is one more trick worth learning, because it is the actual published rule rather than a rough guide. Cirrocumulus, altocumulus and stratocumulus all look like lumpy layers and can only be told apart by apparent size at arm's length: under one finger width, one to three fingers, or wider than your fist. You are not measuring the lumps. You are measuring how far away they are.
Asperitas Is Not a Cloud Type, and the Difference Matters
Asperitas is the dramatic, rippling, upside-down-seascape formation that went viral repeatedly through the 2010s, and it is almost always described as a new cloud type. It is not one. Cloud taxonomy runs in levels — genus, then species, then variety, then supplementary features and accessory clouds — and asperitas sits in that last group. It describes a texture that attaches to a host cloud rather than a cloud in its own right, which is the same rank as the mammatus pouches in the final identification question.
None of which makes it minor. Asperitas reached the 2017 atlas largely because members of the Cloud Appreciation Society kept photographing it and pressing for recognition, which makes it one of very few classifications in the atlas driven by amateur observers rather than meteorological agencies. It is the same argument as the GLOBE data matches, arriving from a different direction entirely: people looking up still change what the official record contains.
The genus/species distinction is also the difference between question nine and question ten in the quiz above. Those stacked lens shapes parked motionless over a mountain ridge are altocumulus lenticularis — a species, not a genus. And the stillness is the best part: the air is moving through at full wind speed the whole time. It condenses climbing the crest of a standing wave and evaporates coming down the other side, so the cloud holds position while the air absolutely does not.
The Dullest Cloud on Earth Is the One Modellers Watch Hardest
Stratocumulus is the low, lumpy, grey-white deck that covers a normal overcast afternoon. It is the most common cloud type on the planet, blanketing roughly 20% of the low-latitude oceans at any given moment, and it is almost certainly the cloud you have looked at most often without ever naming. It is also, by some distance, the one that worries climate modellers most.
Those decks are bright, and they sit over dark ocean, so they reflect a great deal of sunlight that would otherwise be absorbed. In 2019 a team led by Tapio Schneider published large-eddy simulations in Nature Geoscience suggesting that above roughly 1,200 ppm of atmospheric CO₂ those decks stop being stable and break up into scattered cloud — and that the breakup alone would add about 8 °C of global warming on top of the warming from the CO₂ itself, closer to 10 °C in the subtropics. Worse, it shows hysteresis: once broken, the decks only re-form when concentrations fall well below the level that broke them.
Two honest caveats. The 1,200 ppm figure is a rough threshold from an idealised simulation of one representative region, not a firm number, and current concentrations are nowhere near it. But it illustrates why clouds remain the largest single source of uncertainty in climate sensitivity estimates. The most ordinary cloud in the sky is holding one of the biggest open questions in the field — which is a reasonable thing to bear in mind if the quiz above handed you stratocumulus and you read it as the boring result.
Which Clouds Do People Mix Up Most Often?
Cloud identification errors are not random. They cluster into a handful of specific pairs, and every one of them comes down to two genera sharing an altitude band or a form while differing on the third reading.
| Confused pair | Why they look alike | The observation that settles it |
|---|---|---|
| Altostratus vs. nimbostratus | Both are featureless grey mid-level sheets | Altostratus shows the sun as a pale disc through ground glass. Nimbostratus blots it out completely. |
| Cirrostratus vs. altostratus | Both are thin veils covering the whole sky | A 22° halo means cirrostratus. Altostratus cannot make one — its particles are the wrong shape. |
| Stratus vs. stratocumulus | Both are low grey layers | Any visible lumps, rolls or breaks make it stratocumulus. Stratus is genuinely featureless. |
| Cumulus congestus vs. cumulonimbus | Both are tall, bright, hard-edged towers | Cauliflower top, still congestus. Once it glaciates and flattens into an anvil, it is cumulonimbus. |
| Cirrocumulus vs. altocumulus | Both are rippled layers of rounded elements | Elements narrower than one finger at arm's length are cirrocumulus. One to three fingers is altocumulus. |
Something worth reporting about this cloud identification quiz itself, because it was not designed in: when the matching model was tested by simulating people answering consistently in character, its own mistakes landed on those exact pairs. Playing to altostratus most often returned nimbostratus; playing to stratocumulus most often returned stratus; playing to cumulonimbus most often returned cumulus. Not one of the confusions crossed to an unrelated genus. The four dimensions the personality half measures are close enough to the real classification geometry that the model gets confused in the same places human observers do.
The Ten Genera, and What Each One Reads As
The second half of the quiz answers the what cloud am I question by plotting your four readings against all ten genera and returning whichever one sits closest. The shares below were measured, not estimated — every one of the 390,625 possible answer combinations was run through the scoring. The matcher was deliberately calibrated so each genus appears roughly as often as it does in the actual sky, which is why the ordinary clouds dominate and the rare ones stay rare.
⛈️ Cumulonimbus (7.2%) — the only genus that spans the whole troposphere in one structure, and the only one producing hail, lightning or tornadoes. As a reading it means everything at maximum simultaneously: high energy, hard edges, total release. The anvil top is not decoration, it is the cloud hitting the stratosphere and spreading sideways because it has run out of sky. Storms last about forty minutes for a reason.
🌤️ Cumulus (12.1%) — the fair-weather heap children draw, with a flat base and a bulging cauliflower top. All the convection of a storm cloud and almost none of the release. Every cumulus in an airmass shares a base height because that is the precise altitude where rising air surrenders its water. Highly legible, genuinely energetic, and one strong updraft away from becoming something much larger.
🌥️ Stratocumulus (14.1%) — the most common cloud on Earth and the most common result here, which is not a coincidence. Moderate on all four dimensions, which reads as unremarkable and is actually the most stable arrangement available. A layer that convection has broken into rolls without separating them: the coverage of a sheet with the texture of a heap.
🌫️ Stratus (11.1%) — the lowest of the ten and physically identical to fog, differing only in whether its base touches the ground. Soft-edged, close in, and releasing drizzle rather than rain. The cost is real: soft edges get read as no edges, and a grey stretch of stratus looks much like a grey stretch of nothing happening.
🌧️ Nimbostratus (8.1%) — the only genus whose definition requires continuous precipitation reaching the ground, and it manages that with no dramatic features at all. Thick enough to blot out the sun entirely. Where cumulonimbus discharges violently in under an hour, nimbostratus delivers for six, and it is the steady rain rather than the storm that actually soaks in.
🌁 Altostratus (9%) — the grey mid-level sheet that shows the sun as a pale disc without an outline, like light through frosted glass. Sits between the ice above and the water below, which is exactly why it cannot throw a halo. Usually a thickening warm front, so it tends to be read as a sign of what is coming rather than as weather in its own right.
🌥️ Altocumulus (11%)— rounded masses in ordered rows at mid-level, each element one to three fingers wide at arm's length. Real convective energy, but patterned rather than piled. A summer morning full of altocumulus is the classic sign of instability higher up, which doubles as a fair description: organised on the surface, with something moving underneath.
🌬️ Cirrus (12.8%)— the highest genus, above six kilometres, built entirely from ice because no liquid water survives up there. Those hooked ends are fallstreaks: it genuinely precipitates, and the ice sublimates away kilometres above anyone's head. Cirrus arrives a day or two ahead of a front, making it the sky's earliest honest signal.
🌕 Cirrostratus (8.8%) — a veil so thin most people never register that the sky changed, since shadows still fall sharply beneath it. The 22° halo is the only giveaway, and no other cloud can produce one. Influence without footprint, with the standing risk that cirrostratus gets logged as clear sky by anyone who has not learned to check.
✨ Cirrocumulus (5.9%)— the rarest result and the rarest genus: the mackerel sky, a fine ice granulation with elements smaller than one finger at arm's length. It requires convection at an altitude that ought to be far too stable for it, so it rarely lasts an hour before decaying into cirrus or cirrostratus. The honest reading is that this configuration is a transitional state.
Your Sky Will Be Different in Twenty Minutes
The useful thing about clouds, as a subject to learn, is the feedback loop. Almost nothing else you could study changes this fast or is this continuously available — walk outside now and there is a live specimen overhead, and in twenty minutes it will have become something else. A cirrostratus veil thickens into altostratus; altostratus lowers into nimbostratus and starts raining. That sequence is a warm front arriving, and once you can name the three stages you can forecast the next several hours from your own doorstep with no instrument at all.
Start with the finger test, since it collapses the hardest third of the problem into one gesture. Then learn the halo, because it is unambiguous — ring around the sun means cirrostratus, always. Those two alone will move most people from three nameable clouds to seven or eight. If you want somewhere for the observations to go, GLOBE Observer takes them and pairs them with whatever satellite passes over you next.
And if you enjoyed sorting yourself against a real classification system rather than an invented one, the what flower am I quiz works the same way, sorting on actual botanical strategy — pollination signal, bloom tempo, chemical defence — instead of favourite colour. The planet quiz stays overhead and goes considerably further up, and the dinosaur quiz uses the same two-part structure as this one: a sourced knowledge half, then a matching half.
