**Cloud Identification Chart — Name Any Cloud in Three Questions**

> Free cloud identification key covering 29 cloud types and sky features. Filter by height, shape and cover, and read what each one says about the weather.

Source: https://orvik.app/tools/cloud-identifier/ · updated: 2026-09-03

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# What cloud is that?

The World Meteorological Organization recognises ten cloud genera and every cloud in the sky is one of them. Three questions get you there: **how high is it, is it heaped or layered, and can you see the sun through it?** Each entry also says what the cloud means, because a cloud is a reading of the atmosphere rather than a decoration.

Entries **29** Filters **4** Updated **2026-09-03** Cost **Free, no account**

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Height

High clouds are ice and look white and thin; low clouds are water and look grey and solid.

High — above 6 km / 20,000 ft Middle — 2 to 6 km Low — below 2 km Towering through all levels At ground level

Shape

Heaped, with a flat base Flat featureless sheet Wispy, fibrous, streaked Patches, rolls or ripples Tall tower or anvil Smooth lens or saucer Ragged and shapeless

Can you see the sun through it?

Yes, sharply — it is thin Yes, with a ring or halo A dim disc, as if through frosted glass No, the sun is blocked

What it means

Fair weather A front approaching, rain in 12–24 h Rain or snow falling now Thunderstorm risk Strong winds aloft

Showing all 29 clouds

1. ### Cirrus Ci Delicate white streaks and hooks of ice crystal, drawn out by strong high-level wind into what people call mares' tails. Casts no shadow and never produces rain at the ground. Size Base 6–13 km Where Worldwide, at all seasons. Confused with Contrails, which start as straight lines and spread. Cirrus is curved and irregular from the start.
2. ### Cirrostratus Cs A thin milky veil of ice crystals across the whole sky, so subtle you may only notice it because a bright 22-degree halo has appeared around the sun or moon. The halo is diagnostic. Size Base 6–13 km Where Worldwide, ahead of warm fronts. Confused with A hazy sky. If there is a halo, it is cirrostratus, and rain usually follows within 12 to 24 hours.
3. ### Cirrocumulus Cc A fine grain of tiny white ripples with no shading at all — hold your hand at arm's length and each cell is narrower than your little finger. The classic mackerel sky. Size Base 6–13 km; elements under 1° across Where Worldwide but the least common of the high clouds. Confused with Altocumulus, whose elements are larger and have grey shading underneath. If any element is shaded, it is not cirrocumulus.
4. ### Altostratus As A grey-blue sheet over the whole sky through which the sun shows as a pale watery disc with no halo — the textbook phrase is "as if seen through ground glass". Casts no shadows on the ground. Size Base 2–6 km Where Worldwide, ahead of warm fronts. Confused with Cirrostratus above it, which gives a sharp sun and a halo. Once the sun blurs, the deck has come down to altostratus and rain is closer.
5. ### Altocumulus Ac Rounded white and grey patches in regular rows or a broken sheet, each element clearly shaded underneath and about the width of one to three fingers at arm's length. Size Base 2–6 km; elements 1–5° across Where Worldwide, very common. Confused with Stratocumulus, which is lower and whose elements are wider than three fingers.
6. ### Altocumulus castellanus Ac cas Mid-level cloud sprouting small turrets from a common base, like a row of battlements. It signals instability aloft, and on a summer morning it is the single most reliable sign of afternoon thunderstorms. Size Base 2–6 km Where Warm-season continental interiors.
7. ### Nimbostratus Ns A thick dark grey featureless layer that blots out the sun completely and rains or snows steadily for hours. Ragged shreds of cloud drift beneath it in the falling precipitation. Size Base 0.5–3 km, deep Where Worldwide, in frontal systems. Confused with Stratus, which is lower and produces only drizzle. If steady rain has been falling for an hour, it is nimbostratus.
8. ### Stratus St A uniform grey layer with no structure, low enough to hide hilltops, giving drizzle or nothing at all. The sun may show as a distinct outline when it is thin — unlike altostratus, where it is a blur. Size Base 0–2 km Where Coasts, valleys and cool mornings everywhere. Confused with Fog. Stratus that reaches the ground is fog, and the two are the same cloud measured differently.
9. ### Stratocumulus Sc Lumpy grey and white rolls or patches covering most of the sky with narrow blue channels between them, each element wider than three fingers at arm's length. Rarely produces more than light drizzle. Size Base 0.5–2 km; elements over 5° across Where The most common cloud on Earth by area.
10. ### Cumulus humilis Cu hum Small detached white heaps with flat bases all at the same height and crisp cauliflower tops, wider than they are tall. The fair-weather cloud, and reliably so. Size Base 0.5–2 km, wider than tall Where Worldwide, on sunny days over land. Confused with Nothing much. The flat base at a uniform level is what identifies the whole cumulus family.
11. ### Cumulus congestus Cu con A cumulus that has grown taller than it is wide, with hard sharply outlined cauliflower tops still made of water droplets. Also called towering cumulus, and it produces showers. Size Tops to 6 km Where Warm humid air masses worldwide. Confused with Cumulonimbus, which it becomes. The moment the top loses its hard edge and goes fibrous, it has glaciated and it is a storm.
12. ### Cumulonimbus Can injure you Cb A cloud that spans the whole troposphere, with a dark base, hard towering sides and a fibrous top spreading downwind into a flat anvil. Produces lightning, hail and every severe weather phenomenon there is. Size Base under 2 km, tops 12–20 km Where Worldwide; the tallest clouds there are. Risk Lightning strikes up to 15 km from the parent storm, well outside the rain. If you can hear thunder, you are within range; go inside.
13. ### Anvil (incus) Cb inc The flat fibrous top of a cumulonimbus, spread sideways where the updraught hit the stable tropopause and could rise no further. Its downwind edge tells you which way the storm is moving. Size Can spread 100 km downwind Where With every mature thunderstorm.
14. ### Overshooting top Can injure you A rounded bulge pushing up through the smooth anvil, meaning the updraught was strong enough to punch past the tropopause. Visible from tens of kilometres away and a reliable sign of a severe storm. Size A dome above the anvil Where Severe storms worldwide. Risk Overshooting tops indicate very strong updraughts — large hail and damaging wind are likely under that storm.
15. ### Shelf cloud (arcus) Can injure you A low wedge attached to the storm base, with a smooth rising front and a ragged turbulent underside, advancing ahead of the rain. Wind hits within minutes of it passing overhead. Size A wedge across the storm's leading edge Where Ahead of squall lines and strong storms. Confused with A wall cloud, which hangs below the base at the rain-free rear of a storm and rotates. A shelf is at the front and does not rotate. Risk A shelf cloud means a gust front. Get indoors and off the water before it arrives.
16. ### Wall cloud Can injure you An isolated lowering hanging beneath the rain-free base at the rear of a storm, often visibly rotating. It marks the main updraught and it is where tornadoes form. Size A block lowered below the storm base Where Supercells, mainly in the US Great Plains and Midwest. Risk A rotating wall cloud is a tornado warning situation. Take shelter and monitor official alerts rather than watching it.
17. ### Mammatus Rows of smooth hanging pouches on the underside of an anvil, lit dramatically at sunset. They form in sinking air and mean the storm is mature — usually on its departing side, not its leading edge. Size Pouches 1–3 km across Where Under the anvils of severe storms.
18. ### Altocumulus lenticularis Ac len A smooth almond or saucer, sometimes stacked in layers like a pile of plates, hanging motionless in a strong wind while the air streams through it. Standing waves over a ridge. Size Base 2–8 km Where Downwind of mountain ranges everywhere. Confused with Reported as a UFO more often than any other cloud, because it is smooth-edged and does not move.
19. ### Kelvin-Helmholtz waves A row of curling breaking waves along the top of a cloud layer, exactly like surf. Forms where two layers move at different speeds; it lasts a couple of minutes. Size Breaking crests, a few hundred metres Where Rare, worldwide, and brief.
20. ### Asperitas A chaotic wave-torn underside like the surface of a rough sea seen from below. Added to the WMO cloud atlas in 2017 — the first new formal cloud feature in over half a century. Size Across a whole sky Where Worldwide but uncommon; particularly noted in the US Plains.
21. ### Virga Trails of precipitation hanging beneath a cloud and stopping in mid-air, because the drops evaporate before they reach the ground. Curved streaks, often catching the light. Size Streaks hanging below a base Where Dry climates especially.
22. ### Pileus A smooth thin cap sitting briefly on top of a rising cumulus tower, formed as the tower lifts the moist layer above it. It lasts a minute or two and marks a vigorous updraught. Size A thin cap a few km across Where Over strongly growing cumulus.
23. ### Fractus and scud Torn shapeless fragments of low cloud racing beneath a rain-producing deck, formed in the saturated air of falling precipitation. Detached from the main base, which is how you separate it from a wall cloud. Size Small ragged shreds Where Under raining cloud everywhere.
24. ### Fog Stratus cloud at ground level. Radiation fog forms in a valley on a clear calm night and burns off by mid-morning; advection fog rolls in off cold water and can last for days. Size Visibility under 1 km by definition Where Valleys, coasts and cold clear nights worldwide.
25. ### Contrails Straight white lines behind aircraft. Whether they persist is a real weather signal: contrails that vanish in seconds mean dry air aloft and settled weather, while contrails that spread into sheets mean the upper air is already near saturation and a front is on the way. Size Base 8–12 km Where Under any busy flight path.
26. ### Noctilucent clouds Electric-blue filaments glowing against a deep twilight sky an hour or two after sunset, when everything else is dark. They are ice on meteoric dust in the mesosphere, lit by a sun that has already set for the ground. Size About 80 km up — the highest clouds there are Where Latitudes 50–70°, in the weeks around midsummer.
27. ### Nacreous clouds Iridescent mother-of-pearl bands in pastel pink, green and gold, glowing well after sunset in a very cold winter twilight. Beautiful, rare, and involved in polar ozone destruction. Size About 20 km up, in the stratosphere Where High latitudes in deep winter: Scandinavia, Alaska, Scotland, Antarctica.
28. ### Pyrocumulus Can injure you A dirty grey-brown cumulus growing directly out of a smoke plume, driven by the heat of the fire below. In its most extreme form it generates its own lightning and its own wind. Size Tops to 10 km in extreme cases Where Over large wildfires and volcanic eruptions. Risk A pyrocumulus over a wildfire indicates extreme fire behaviour and erratic winds. Treat it as a signal to leave the area.
29. ### Roll cloud (volutus) A long horizontal tube of cloud rolling about its own axis, completely detached from any other cloud. Unlike a shelf cloud it is not attached to a storm base. Size A tube up to hundreds of km long Where Rare; the Morning Glory over the Gulf of Carpentaria is the famous example.

Nothing in this key matches every filter at once. That usually means one observation is
off — a colour read in shade, or a size guessed rather than measured. Clear the filter you
are least sure about and look again.

## Ten genera, two questions

The classification everyone still uses was proposed by Luke Howard in 1802 and codified by the World Meteorological Organization. It is built on two Latin roots and a modifier, and once you have those the whole scheme unpacks itself.

- **Cumulus** — heap. Convective, lumpy, with a flat base where rising air reached its condensation level.
- **Stratus** — layer. Formed by air lifted or cooled across a broad area, so it is flat and featureless.
- **Cirrus** — curl of hair. High and made of ice, so it is white, fibrous and casts no shadow.
- **Nimbus** — rain. Attached to the two genera that actually precipitate: nimbostratus and cumulonimbus.
- **Alto-** — the middle level, 2 to 6 km.

Combine them and the ten genera fall out: cirrus, cirrostratus and cirrocumulus high; altostratus and altocumulus in the middle; stratus, stratocumulus and nimbostratus low; cumulus and cumulonimbus vertical. There is no eleventh.

The height question is easier than it sounds because you do not have to measure anything. **High clouds are white and cast no shadow on themselves**, since ice crystals are sparse and translucent. **Low clouds have grey undersides**, because liquid water is dense enough to block light. Shading is a proxy for altitude and it is reliable.

## The finger test, and why element size matters

Cirrocumulus, altocumulus and stratocumulus all look like patterned patches of cloud, and they sit at three different heights. Meteorologists separate them by apparent element size, which is a proxy for distance, and you measure it with your hand.

Hold your arm straight out. Your little finger covers about one degree of sky, three fingers about five degrees, and a clenched fist about ten.

*Separating the three cumuliform layer clouds by apparent element width, following WMO practice.*

| Element width at arm's length | Angular size | Cloud | Shading |
| --- | --- | --- | --- |
| Narrower than one little finger | Under 1° | Cirrocumulus | None — pure white |
| One to three fingers | 1–5° | Altocumulus | Clear grey shading below |
| Wider than three fingers | Over 5° | Stratocumulus | Heavy grey |

The shading column is the shortcut. Cirrocumulus is ice and never shades; if any element in the pattern has a grey underside, you are looking at altocumulus or lower. That one observation resolves the three faster than the finger measurement does.

## Reading a warm front arriving

The most useful thing amateur cloud watching gives you is the ability to see a front coming twelve to twenty-four hours out, from the ground, with no equipment. A warm front approaches as a shallow wedge, so its cloud deck arrives high and thin and steadily lowers and thickens. The sequence is fixed:

1. **Cirrus.** Wispy hooks appear from the direction the weather comes from. Rain is roughly a day away.
2. **Cirrostratus.** The wisps merge into a milky veil and **a halo appears around the sun or moon**. This is the classic marker, and the old rhyme — a ring around the moon means rain soon — is meteorologically sound.
3. **Altostratus.** The veil thickens and the sun blurs into a watery disc with no halo and no shadows on the ground. Rain is now within hours.
4. **Nimbostratus.** The sun disappears, the base lowers, ragged scud races underneath, and steady rain begins and continues.

A cold front behaves completely differently: it is steep, so it produces a narrow line of towering cumulus and cumulonimbus with little warning, a short violent burst of rain and wind, and then a rapid clearance into cool air with fair-weather cumulus. If the sky went from blue to a black wall in twenty minutes, that is a cold front.

## The clouds that mean take shelter

Four sky features are worth recognising for reasons that are not aesthetic.

**Cumulonimbus.** Any cloud with a hard towering side and a fibrous spreading top. Lightning strikes routinely up to 15 km from the parent cloud, into air that looks clear — the "bolt from the blue" is a real and documented phenomenon. The operative rule is simple and is the one the US National Weather Service publishes: **if you can hear thunder, you are close enough to be struck.** Go inside, and wait 30 minutes after the last thunder before going back out.

**Shelf cloud.** A wedge on the leading edge of a storm, smooth on top and ragged underneath, advancing ahead of the rain. It marks a gust front, and damaging straight-line winds arrive within minutes of it passing over. This is the one that catches people on lakes and beaches.

**Wall cloud.** An isolated lowering under the rain-free base at the back of a storm. If it is rotating, that is the mesocyclone, and tornadoes form there. It is not the same thing as a shelf cloud, and confusing the two costs people the time they need.

**Overshooting top.** A dome punching up through an otherwise flat anvil. It means the updraught beat the tropopause, which is a strong indicator of severe hail and wind. Visible from a long way off, which makes it useful for deciding whether to drive on.

None of this replaces a warning. Radar sees rotation you cannot, and official alerts should always take priority over what the sky looks like from where you are standing.

## Optical effects, and what they tell you about the cloud

Halos and coronas are frequently mistaken for each other and they say opposite things about what the cloud is made of.

A **22-degree halo** is a large ring around the sun or moon, about the span of a hand at arm's length, produced by refraction through hexagonal ice crystals. A halo means ice, which means high cloud, which usually means cirrostratus and an approaching front. Sundogs — bright spots on either side of the sun at the same height — come from the same crystals settling flat.

A **corona** is a small coloured disc tight around the sun or moon, produced by diffraction through water droplets. It means liquid, so a lower cloud, and the smaller and more colourful the corona the more uniform the droplet size. **Iridescence** at cloud edges is the same effect, and it is what makes nacreous clouds spectacular.

A **glory** is a set of coloured rings around the shadow of your own head, seen from an aircraft or a mountaintop looking into cloud below. A **crepuscular ray** is a shaft of sunlight through a gap, made visible by haze, and it says nothing about the cloud at all.

## Photographing and reporting clouds

Clouds are one of the few subjects where a phone camera is genuinely adequate, provided you handle two problems.

**Exposure.** Auto exposure meters for the whole frame and blows out the cloud, which is the brightest thing in it. Tap the brightest part of the cloud to expose for it and let the foreground go dark, or drag the exposure slider down a stop.

**Scale.** A photograph of nothing but sky has no reference, and the same frame could be a small cumulus at two kilometres or a supercell at forty. Include a horizon, a tree line or a rooftop. That single decision is what makes a cloud photograph identifiable later.

If you want the observation to be useful to somebody, note the time, your location and which direction you were facing, and whether the cloud was moving. The Cloud Appreciation Society and the WMO International Cloud Atlas both accept submissions, and national weather services in most countries run spotter networks that take severe-weather reports from the public. In the United States that is SKYWARN, which trains volunteers and feeds their reports straight into warning decisions.

29 entries here cover the ten genera plus the supplementary features and special clouds people actually photograph. The full WMO atlas adds species, varieties and accessory clouds in combinations running to over a hundred names — cumulus radiatus, stratocumulus undulatus and the rest — which is more precision than the sky usually rewards from the ground.

## Questions people ask about this

What are the ten types of cloud?

High: cirrus, cirrostratus, cirrocumulus. Middle: altostratus, altocumulus. Low: stratus, stratocumulus, nimbostratus. Vertical: cumulus and cumulonimbus. Every cloud in the sky belongs to one of these ten genera; everything else is a species, variety or supplementary feature added to one of them.

What does a ring around the sun or moon mean?

A 22-degree halo is refraction through hexagonal ice crystals in cirrostratus, a high thin cloud that typically runs ahead of a warm front. Rain often follows within 12 to 24 hours, so the folk rhyme about a ring around the moon has a real mechanism behind it. Do not confuse it with a corona, which is a small tight coloured disc caused by water droplets in lower cloud.

Which clouds mean a thunderstorm is coming?

Cumulonimbus is the storm itself — a cloud spanning the whole troposphere with a dark base and a fibrous anvil top. The early warning is cumulus congestus, a cumulus grown taller than it is wide with hard cauliflower tops; when those tops turn fibrous the cloud has glaciated and become a storm. On a summer morning, altocumulus castellanus — mid-level cloud sprouting little turrets — is the most reliable indicator of afternoon storms.

What is the difference between a shelf cloud and a wall cloud?

A shelf cloud is attached to the leading edge of a storm, wedge-shaped, smooth on top and ragged below, and it marks the gust front — damaging wind arrives within minutes. A wall cloud hangs below the rain-free base at the rear of the storm, is isolated rather than attached along a front, and often rotates; it marks the updraught where tornadoes form. Both mean take shelter, and they arrive at different moments.

What is that smooth lens-shaped cloud over the mountains?

Altocumulus lenticularis, formed in a standing wave downwind of a ridge. Air rises over the obstacle, condenses at the crest of the wave, and evaporates again as it descends, so the cloud stays in one place while a strong wind streams through it. That combination of smooth edges and apparent stillness is why it is the most commonly reported UFO in the sky.

Why do some contrails disappear and others spread across the sky?

Humidity at cruising altitude. When the upper air is dry, the ice crystals in an aircraft exhaust sublimate within seconds. When it is already near saturation, the crystals persist and spread into cirrus-like sheets. Persistent spreading contrails are therefore a genuine sign of moist upper air, which often means a front approaching in the next day.

Is fog a cloud?

Yes — it is stratus cloud that reaches the ground, and the only difference between them is where the base sits relative to you. Radiation fog forms in valleys on clear calm nights as the ground cools and burns off through the morning; advection fog forms when warm moist air moves over a cold surface, which is what rolls in off the sea and can persist for days.

## Still not sure? Point a camera at it

A filter narrows clouds down to a shortlist. Orvik reads the photo itself and names the species, with the look-alikes ranked underneath so you can check the call yourself.

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## Where the data comes from

- [WMO International Cloud Atlas](https://cloudatlas.wmo.int/)
- [WMO International Cloud Atlas — the genera, in full](https://cloudatlas.wmo.int/en/clouds-genera.html)
- [NWS — lightning safety](https://www.weather.gov/safety/lightning)
- [Cloud Appreciation Society — cloud identification](https://cloudappreciationsociety.org/the-clouds/)

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