altitudeHow high up a thing is, with sea level as zero. Cloud heights are given as altitudes. Contrails form at the altitudes where jets cruise, in the level of the high clouds.
cirrusA high, wispy cloud that looks like strands of hair. The name is Latin for a curl of hair. Cirrus clouds are always made of ice crystals.
cloudWater you can see in the sky: countless tiny drops. Clouds form when water vapor in the air condenses. A cloud can be made of water droplets, ice crystals or both.
condensationWhat happens when vapor cools and becomes liquid. Cloud droplets form by condensation when rising air cools enough.
cumulonimbusThe giant cloud that thunderstorms come from. It often spreads out at the top in the shape of an anvil, and it can bring hail and tornadoes. Its top reaches the level of the highest clouds.
cumulusA heaped-up, cotton-like cloud with a level bottom. The name is the Latin word for a heap. Cumulus clouds form low, mostly less than 2,000 meters up.
Show all 36 terms (30 more)
Cloud basics, continued
dropletA bead of liquid almost too small to see. A cloud droplet measures a few thousandths of a millimeter across, small and light enough to stay up in the air.
fogThick cloud lying so low that you are inside it. By definition, fog cuts how far you can see to less than 1 kilometer.
ice crystalA tiny piece of ice with a regular, six-sided shape. Ice crystals grow as six-sided columns, flat plates and branching stars.
nimbusThe old Latin name for a rain cloud. A cloud with nimbo or nimbus in its name brings rain or snow: nimbostratus and cumulonimbus.
stratusA low, even layer of gray that may bring drizzle. Stratus is from the Latin word for layer. Stratus clouds spread wide like a blanket, and their edges are blurred.
water vaporThe unseen gas that evaporation adds to the air. It is always in the air around us, though we cannot see it. When air rises and cools, some of it condenses.
More cloud types 12
altocumulusMid-level patches of small, rounded cloud lumps. It is the most common mid-level cloud. With your arm held out straight, each lump looks wider than a little finger and narrower than three fingers.
altostratusA gray mid-level sheet with the sun dim behind it. The sun looks as if it were seen through ground glass, and things on the ground cast no shadows.
cirrocumulusA thin, high cloud broken into tiny white grains. Each grain looks smaller than a little finger held at arm's length. The cloud is mostly ice crystals and does not last long.
cirrostratusA high, see-through veil of ice-crystal cloud. It can cover the whole sky, and it nearly always puts a halo around the sun or moon.
contrailA thin streak of cloud drawn across the sky by a jet. The word is short for condensation trail. Contrails are made mostly of ice crystals.
lenticular cloudA smooth cloud shaped like a lens or a saucer. It forms where wind is pushed up and over a mountain, and it stays in one place while the wind blows on.
mackerel skyRows of rippled cloud that look like fish scales. The clouds are cirrocumulus or altocumulus. The pattern often means a change in the weather is coming.
mistA light haze of water drops that only dims the view. Mist and fog form in the same way. Mist is thinner and easier to see through, and it usually clears sooner.
nimbostratusA thick, dark layer cloud of steady rain or snow. It is thick enough to blot out the sun, and it brings no thunder or lightning.
noctilucent cloudA faint, glowing cloud seen high up after sunset. The name roughly means night shining. These thin clouds of ice crystals form higher than any others and are seen on summer nights far from the equator.
stratocumulusLow, lumpy rolls or patches of gray and white cloud. Each lump looks wider than three fingers held up at arm's length.
towering cumulusA tall cumulus that may grow into a storm cloud. Its other name is cumulus congestus. It is the stage between a middling cumulus and a cumulonimbus.
How clouds form 12
cloud baseThe level where the bottom of a cloud lies. It is measured with a ceilometer, which finds the height from a light beam bounced back by the cloud.
cloud coverThe share of the sky that clouds hide. On average, clouds cover about two thirds of the Earth.
condensation nucleiTiny specks in the air that droplets form around. The specks are smoke, sea salt, dust and soil. Each is about one hundredth the size of the droplet that forms on it.
dew pointHow cool air must get before its vapor condenses. How high the dew point is depends on the amount of vapor in the air. In very dry air it is low, and the air must cool a long way before anything condenses.
evaporationThe slow drying-up of water into the air as vapor. It happens at the surface of the water, and it does not need boiling heat.
high cloudA cloud of the top level, such as cirrus. Over the middle latitudes high clouds form 16,500 to 45,000 feet (5 to 14 kilometers) up. They are thin and white.
low cloudA cloud of the bottom level, such as stratus. Its base lies within about 6,500 feet (2 kilometers) of the ground.
middle cloudA cloud of the mid level, such as altocumulus. In Latin alto means high, yet the alto clouds are the middle ones, about 6,500 to 23,000 feet (2 to 7 kilometers) up in the middle latitudes.
oktaA unit of cloud cover, worth an eighth of the sky. A clear sky is 0 oktas and a sky fully covered by cloud is 8.
saturationThe state of air that holds all the vapor it can. Saturated air has a relative humidity of 100 percent.
supercooled waterLiquid water that is colder than freezing. Droplets of it are common in stratus and cumulus clouds. They can freeze onto an aircraft that flies through them and ice its wings.
updraftAir on the move upward, as inside a growing cloud. Rising air cools as it climbs, by about 5.5 degrees Fahrenheit for every 1,000 feet (9.8 Celsius a kilometer) until a cloud starts to form.
How this list was compiled: Term list chosen for this site on 2026-10-12. Each meaning is written in our own words and was checked that day against the article on the term in the English Wikipedia (https://en.wikipedia.org/), whose text is under the Creative Commons Attribution-ShareAlike license: Cloud, Cumulus cloud, Stratus cloud, Cirrus cloud, Nimbostratus cloud, Cumulonimbus cloud, Fog, Condensation, Water vapor, Altitude, Drop (liquid), Ice crystal, Stratocumulus cloud, Altocumulus cloud, Altostratus cloud, Cirrocumulus cloud, Cirrostratus cloud, Contrail, Lenticular cloud, Mist, Noctilucent cloud, Mackerel sky, Cumulus congestus cloud, Evaporation, Dew point, Humidity, Cloud condensation nuclei, Vertical draft, Supercooling, Cloud base, Cloud cover, Okta, Cloud physics and List of cloud types. Nimbus, cumulus and okta were also read in Wiktionary, the free dictionary (https://en.wiktionary.org/). The four core clouds and their Latin names, the ten basic clouds and what each looks like, the three levels and their heights, condensation nuclei, the dew point, saturation, the cooling of rising air and the color of clouds were checked a second time against JetStream, the online weather school of the U.S. National Weather Service (https://www.noaa.gov/jetstream/clouds: How Clouds Form, The Four Core Types of Clouds, Ten Basic Clouds, The Color of Clouds). Water vapor, droplets, lenticular clouds and the heights of contrails were checked against the Center for Science Education of the University Corporation for Atmospheric Research (https://scied.ucar.edu/learning-zone/clouds: Clouds and How They Form, Cloud Types). The heights given for high and middle clouds are JetStream's for the middle latitudes. The fact after each meaning is from the same pages. Licence: own work
How it works
This cloud vocabulary worksheet lists cloud, cumulus, stratus, cirrus, nimbus, cumulonimbus, fog, condensation, water vapor, altitude, droplet and ice crystal beside their meanings in another order. The answers are drawn in on a last page.
Read the full guide
More cloud types
Set opens on Cloud basics. The second set has nimbostratus, stratocumulus, altocumulus, altostratus, cirrocumulus, cirrostratus, contrail, lenticular cloud, mist, noctilucent cloud, mackerel sky and towering cumulus.
How clouds form
The third set has evaporation, dew point, saturation, condensation nuclei, updraft, supercooled water, cloud base, cloud cover, okta, high cloud, middle cloud and low cloud.
Rain, snow, hail, thunder and the tools of a forecaster are on the weather word search.
Questions and answers
What are the 4 main types of clouds?
Cirrus, cumulus and stratus, plus nimbus, the rain cloud. Luke Howard set out these four in 1803, and the names of today's ten basic clouds are built from them.
What are the 10 types of clouds?
Cirrus, cirrocumulus and cirrostratus are the high clouds. Altocumulus, altostratus and nimbostratus are in the middle. Cumulus, stratus, stratocumulus and cumulonimbus are low, though a cumulonimbus towers up through all three levels.
How do clouds form?
Air rises and cools. When it has cooled to its dew point, its water vapor condenses onto tiny specks of dust, smoke or salt, and the droplets that form make a cloud. Air is pushed up by warm ground, by mountains and by weather fronts.
Why are clouds white?
A cloud's droplets are about as big as the waves of sunlight, so they scatter every color of the light equally, and all the colors together look white. A thick cloud looks gray because less sunlight gets through it.