Cloud Types
Most clouds are associated with weather. These clouds can be divided into groups mainly based on the height of the cloud's base above the Earth's surface. The following table provides information about cloud groups and any cloud classes associated with them. In addition, some clouds don't fall into the categories by height. These additional cloud groups are listed below the high, middle, and low cloud groups.
High-Level Clouds High-level clouds form above 20,000 feet (6,000 meters) and since the temperatures are so cold at such high elevations, these clouds are primarily composed of
ice crystals. High-level clouds are typically thin
and white in appearance, but can appear in a magnificent array of colors when the sun is low on the horizon.
Cirrus
Cirrus clouds are the most common of the High Cloud (5000-13000m) group. They are composed entirely of ice and consist of
long, thin, wispy streamers. They are commonly known as "
mare's tails" because of their appearance.
Cirrus clouds are usually white and predict fair weather.
Cirrocumulus
Cirrocumulus clouds belong to the High Cloud group (5000-13000m). They are
small rounded puffs that usually appear in long rows. Cirrocumulus are usually
white, but sometimes appear gray. Cirrocumulus clouds are the same size or smaller than the width of your littlest finger when you hold up your hand at arm's length.
If these clouds cover a lot of the sky, it is called a "
mackerel sky" because the sky looks like the scales of a fish. Cirrocumulus are usually seen in the winter time and indicate fair, but cold weather.
Cirrostratus
Cirrostratus clouds belong to the High Cloud (5000-13000m) group. They are
sheetlike thin clouds that usually cover the entire sky.
The sun or moon can shine through cirrostratus clouds . Sometimes, the sun or moon will appear to have a halo around it when in the presence of cirrostratus. The ice crystals from the cloud refracts the light from the sun or moon, creating
a halo. This halo is the width of your hand when you hold it out at arm's length.
Cirrostratus clouds usually come 12-24 hours before a rain or snow storm. This is especially true if Middle group clouds are associated with it.
Mid-Level Clouds The bases of mid-level clouds typically appear between
6,500 to 20,000 feet (2,000 to 6,000 meters). Because of their lower altitudes, they are composed primarily of water droplets, however, they can also be composed of ice crystals when temperatures are cold enough.
Altocumulus
Altocumulus clouds are part of the Middle Cloud group (2000-7000m up). They are
grayish-white with one part of the cloud darker than the other. Altocumulus clouds usually form in groups and are about 1 km thick.
Altocumulus clouds are about as wide as your thumb when you hold up your hand at arm's length to look at the cloud.
If you see altocumulus clouds on a warm humid morning, then expect thunderstorms by late afternoon.
Altostratus
Altostratus belong to the Middle Cloud group (2000-7000m up). An altostratus cloud usually covers the whole sky and has a
gray or blue-gray appearance. The sun or moon may shine through an altostratus cloud, but will appear watery or fuzzy.
An altostratus cloud usually forms
ahead of storms with continuous rain or snow. Occasionally, rain will fall from an altostratus cloud. If the rain hits the ground, then the cloud becomes classified as a nimbostratus cloud.
Low-level Clouds Low clouds are of mostly composed of water droplets since their bases generally lie
below 6,500 feet (2,000 meters). However, when temperatures are cold enough, these clouds may also contain ice particles and snow.
Stratus
Stratus clouds belong to the Low Cloud (surface-2000m up) group. They are uniform
gray in color and can cover most or all of the sky. Stratus clouds can look like a
fog that doesn't reach the ground.
Light mist or drizzle is sometimes associated with stratus clouds.
Stratocumulus
Stratocumulus clouds belong to the Low Cloud (surface-2000m) group. These clouds are
low, lumpy, and gray. These clouds can look like cells under a microscope - sometimes they line up in rows and other times they spread out.
Only light precipitation, generally in the form of drizzle, occurs with stratocumulus clouds. To distinguish between a stratocumulus and an altocumulus cloud, point your hand toward the cloud. If the cloud is about the size of your fist, then it is stratocumulus.
Nimbostratus
Nimbostratus clouds belong to the Low Cloud (surface to 2000m up) group. They are
dark gray with a ragged base.
Nimbostratus clouds are associated with continuous rain or snow. Sometimes they cover the whole sky and you can't see the edges of the cloud.
Cumulonimbus
Cumulonimbus clouds belong to the Clouds with Vertical Growth group.
They are generally known as thunderstorm clouds. A cumulonimbus cloud can grow up to 10km high. At this height, high winds will flatten the top of the cloud out into an anvil-like shape.
Cumulonimbus clouds are associated with heavy rain, snow, hail, lightning, and tornadoes.
Cumulus
Cumulus clouds belong to the Clouds with Vertical Growth group.
They are puffy white or light gray clouds that look like floating cotton balls. Cumulus clouds have sharp outlines and a flat base. Cumulus clouds generally have a base height of 1000m and a width of 1km.
Cumulus clouds can be associated with good or bad weather. Cumulus humilis clouds are associated with fair weather. Cumulus congestus clouds are usually associated with bad weather. Their tops look like cauliflower heads and mean that light to heavy showers can occur.
Here's a tip on how to know if you see a cumulus cloud in the sky. Cumulus cloud cells (the individual puffs of clouds) are about the size of your fist or larger when you hold up your hand at arm's length to look at the cloud.
