Four Winds Nature Institute
4 Casey Rd. Chittenden, VT 05737
802-353-9440
www.fourwindsinstitute.org
Kinds of Clouds
Cumulus clouds are billowy white clouds that form on sunny days as the land heats up and
warm air begins to rise. As the warm air meets colder air aloft, the water vapor condenses into
droplets that scatter light, making the clouds appear white. Cumulus clouds build upwards giving
them a puffy, mounded look. They are generally fair weather clouds, although they can develop
into thunderheads.
Stratus clouds are low, flat clouds that look like a gray blanket covering the sky. They range
from light to dark gray, and can show layering, or appear like a uniform gray covering over the
sky. Stratus clouds form when a layer of warm air meets a mass of colder air above and
condenses at the same height above the ground. Stratus clouds may bring mist, rain or drizzle.
Nimbus clouds are rain clouds. Nimbostratus are dark gray layered clouds that cover the sky
and deliver a steady rain. Cumulonimbus are thunderheads, giant cumulus clouds that build up
to heights of 40,000 to 75,000 feet above the ground. The extreme vertical winds within these
clouds are very dangerous for aircraft. These clouds can produce thunder and lightning, high
winds, drenching rain or hail and even tornadoes.
Cirrus clouds are high, thin, wisps of clouds that often have swirls or curls like a horse’s tail and
so they are called Mare’s Tails. Because they form at great heights, over 25,000 feet high, where
the temperature is always below freezing, they are made of ice crystals. Cirrus clouds are seen in
fair weather conditions, but they are usually followed in two or three days by thickening clouds
and bad weather.
Cirrostratus clouds look like a fine gray veil over the sky. They are high clouds made of ice
crystals rather than water droplets. In the daytime, it is common to see sun dogs (short rainbows
on either side of the sun) when there are cirrostratus clouds. At night you may see a halo around
the moon because of the way the ice crystals bend the light.
Cirrocumulus clouds are finely rippled clouds of very high altitude that, like cirrus clouds, are
made of ice crystals. A sky with cirrocumulus clouds is sometimes called a mackerel sky
because the clouds look like the pattern on a mackerel fish’s skin. This sky is often followed by
thickening clouds and bad weather with rain or snow.
Altocumulus clouds are high patchy cumulus-type clouds that appear to line up in rows and
furrows like a plowed field. These puffy clouds are mid-level clouds, averaging about 10,000
feet above the ground. They are made of water droplets and often bring a change in the weather.
Altostratus clouds are midlevel clouds that form a uniform gray covering over the sky and give
the sun an appearance of being behind frosted glass. They often appear before rain or snow.
Stratocumulus clouds are both layered like stratus and mounded like cumulus. Often seen in
winter, these layers of clouds, puffy rolls in shades of gray, may turn into nimbostratus and then
bring rain or snow.
Four Winds Nature Institute – 4/09