Cloud Types
Introduction
Clouds are classified into __________ types. The names used for the clouds are based
on three factors: the _________ at which the cloud occurs, the __________ of the
cloud, and whether the cloud is producing ___________. This tutorial will help you learn
about the different cloud types so that you can make accurate observations for the
Students’ Cloud Observations On-Line (S’COOL) project.
There are _______ altitude ranges, or cloud levels. The height of the cloud base
determines a cloud’s level. Clouds with a base below __________ meters are
considered low-level clouds. Clouds with a base between ________ ____ ________
are mid-level clouds. Those with a base above _________ meters are considered highlevel clouds.
In 1803, Luke _________ classified four main cloud types with Latin terms. Cumulus
means “_______” and describes heaped, lumpy clouds. Cirrus means “____ __ ____”
and is used to name clouds that look like wispy locks of hair. Featureless clouds that
form sheets are named stratus, meaning “______.” Howard used the term nimbus,
which means “cloud,” to name low, gray rain clouds.
Low-Level Clouds
These pictures show examples of low-level clouds. The Clouds and the Earth’s
________ Energy System (__________) satellite cannot distinguish between individual
cloud types at this level, but calls all of them “low, water clouds.” There is a continuum
among these low-level cloud types, ranging from __________, to nearly overcast, to
individual clouds. This range of low-level clouds is explained in more detail in the next
sections.
True stratus clouds are _________ and _____________. The sky looks flat and
uniform in all directions, appearing white or gray rather than blue. Generally these
clouds obscure the Sun so that its location cannot be pinpointed. When this condition
occurs, the cloud is said to be ___________.
_________ is a special kind of stratus cloud: one that is low enough to touch the
ground. It offers students a good personal experience of what a cloud feels like. In
addition, it allows students to experience some of the conditions necessary for cloud
formation, such as _________ _______ and _______ _____________.
________________ clouds have both layered and puffy characteristics. Cloud cover
tends to be mostly cloudy to overcast, but distinct cloud pieces are visible, in contrast to
the uniform and flat character of stratus clouds. There may be areas of clear blue sky,
but the clouds appear to be part of a large cloud system. These clouds are common in
__________ and _________ areas.
______________ clouds are puffy, individual clouds typically associated with fair
weather. They are the most common type of cloud and are often described as having a
popcorn-like or cotton ball appearance. They are made of water droplets and generally
have sharp outlines. Cumulus clouds occur in a variety of shapes and sizes, and with a
little imagination, you can see all sorts of interesting things in these clouds.
Clouds that produce precipitation are designated with the Latin prefix ________-.
__________________ is a layered, uniform, rain cloud. A cloud can quickly change to
or from nimbostratus; that is, it can quickly start or stop raining during your
observations. In a situation like that, you can pick a cloud type and make a note in the
comments about intermittent rain. These clouds are generally very dark, and are
associated with large areas of continuous rain. Nimbostratus can also produce _______
or ________.
______________ clouds are ____________, meaning that they are formed by the
upward movement of warm air currents. They are accompanied by compensating
downdrafts of cold air. These clouds are most common in warm and humid weather and
can produce thunder, lightning, heavy rain, hail, strong winds, and tornadoes. They can
extend through a large part of the atmosphere. They can even extend beyond the
_____________, which is the boundary between the troposphere (where we live and
where all weather occurs) and the stratosphere (where the ozone layer is). Despite this
range of cloud vertical development, as long as the base of the cloud is below 2,000
meters, it is considered a low-level cloud.
Mid-Level Clouds
There are two mid-level cloud types, designated by the prefix _____-: altocumulus
(puffy) and altostratus (layered). Mid-level clouds may be made up of ice crystals at the
higher altitudes, but they are more often composed of water droplets.
____________ clouds are a mid-level version of cumulus clouds, consisting of cloud
puffs. This cloud type sometimes appears like dozens of small, loose bands or ripples
like waves on a sea. These clouds are often associated with the approach of a weather
front, and may be an indicator of rain on the way.
______________ clouds are the mid-level version of stratus clouds. They are uniform
and diffuse, with little appearance of individual cloud pieces. The sky appears gray or
blue-gray, and sunlight is diffused, as though seen through water or frosted glass. When
the cloud partially blocks the Sun in this way, the cloud is said to be
_________________.
High-Level Clouds
High-level cloud types are identified with the prefix ______-: cirrus (thin and wispy),
cirrostratus (layered), and cirrocumulus (puffy). Because all high-level clouds are made
of ice particles rather than water droplets, they have a fairly distinct appearance. The
boundaries of ice clouds tend to be more diffuse, or fuzzier, than the generally sharp
boundaries of water clouds. They can also produce optical effects such as halos and
sun dogs.
___________ clouds are the classic and distinct high-level cloud. They are sometimes
called “mare’s tails” because they appear to be brushed across the sky and are hair-like
in appearance. Curled ends are common in this cloud type. They are usually quite thin
and wispy, and blue sky is visible through portions of the cloud. These clouds are
generally white.
_____________ clouds are the high-level version of stratus. They are sheet-like, nearly
transparent clouds that cover a large part of the sky. When these clouds are present,
the Sun may appear to be surrounded by a colored halo due to refraction of light by the
ice particles in the cloud.
______________ clouds are the high-level cumulus clouds. They are thin ice clouds
that have a patchy or wavelike appearance.
______________, or condensation trails, are clouds created by airplanes. They are also
found at the high level. Students often mistakenly assume that contrails are smoke and
exhaust from an airplane, but contrails are actually clouds formed when the tiny
particles (aerosols) and warm water vapor in the plane’s exhaust combine with the
ambient water vapor to form ice crystals. The presence and character of contrails can
tell us about the state of the atmosphere along the plane’s flight path. If the air is very
dry and there is not enough water vapor to condense, no cloud forms. If the air is a little
moister, a contrail may form and quickly evaporate (which is called a short-lived
contrail). If the air contains enough water vapor, a contrail may form and remain for
hours (known as a persistent contrail), or even spread to cover very large areas.
Researchers are very interested in these clouds that humans cause. When making
cloud observations, you should therefore note the presence and number of contrails.
Multi-Level Clouds
Some scientists estimate that as much as half the time, more than one cloud level is
present in the sky. When you observe ____________ ________ _________, you
should record the cloud information for each level of cloud that you see—but be careful
to distinguish between different cloud levels and the possible occurrence of more than
one layer of cloud within a given level. When more than one layer of stratus cloud
occurs, for example, you may just note this in the comments.
If a thick, ___________, low layer is present, then you obviously cannot observe
anything about the presence or absence of upper level clouds. In situations like these,
the surface and satellite observations are very complementary: the satellite observes
from above and will see any upper layer clouds, and the observers on the ground can
see the lower level clouds.
Determining Cloud Level
A good way to determine the level of cumulus clouds is to assess the size of the
individual cloud elements. ______-________ cumulus clouds are about the same size,
or larger than, your fist held at arms’ length. One exception to this rule is when a small
cumulus cloud is developing or evaporating. In that case, its direction or speed of
motion may indicate that it is in the same layer as nearby larger cumulus clouds. Midlevel cumulus clouds are farther away and the individual cloud pieces appear
substantially smaller, about the size of your thumb at arms’ length. High-level cumulus
clouds are smaller still, with individual cloud pieces about the size of the nail on your
little finger at arms’ length.
_____________ clouds have no distinct cloud pieces to measure. For these clouds, a
general rule is that cloud opacity tends to decrease with height. Thus, low-level clouds
are generally thicker than mid-level clouds, and a high-level cirrostratus is very thin.
Thus, by observing how much the cloud obscures the Sun, you can estimate the level of
a stratus cloud.
If there is ___________, the chances are very good that you are dealing with a low-level
cloud. Mid-level clouds occasionally precipitate, but this is a rare occurrence.