METEOROLOGIST JEFF HABY
This writing looks at combinations of the basic cloud types (stratus, cumulus, cirrus), naming for the elevation the cloud occurs,
precipitation producing clouds and unique clouds. Below are composite clouds and a brief description of each:
Stratocumulus- A low level stratus cloud that has distinct clumps. They look like a combination of small fair weather cumulus
and a low level stratus deck.
Cirrocumulus- Patches within cirrus clouds that give the appearance of the mackerel sky. The patches
are often arranged in a regular pattern.
Cirrostratus- High clouds composed of ice crystal stratus. The sun will often shine through them. Halos and sun dogs can
be produced as the sun shines through cirrostratus.
Clouds can also be named for the elevation they occur. If the cloud is a low level cloud relative near the surface it will be labeled
with the basic stratus or cumulus depending on which type it is. Upper level clouds will be labeled as cirrus or one
of the two upper level combinations of composite clouds (cirrocumulus and cirrostratus). The additional cloud type is
middle level clouds which can have the “alto” prefix:
Altocumulus- Middle level cumulus clouds. They are composed of liquid drops and have patches of clouds arranged in regular patterns.
Altostratus- Middle level stratus clouds. They tend to be too high and thin to produce significant precipitation but they
can overcast the sky and produce light precipitation.
Precipitation producing deep clouds can be stratiform or cumulus. A description of these clouds follows:
Nimbostratus- A precipitation producing stratus cloud. They develop due to forced broad scale lifting of saturated air and can
cover great distances. Most non-thunderstorm precipitation is produced by nimbostratus.
Cumulonimbus- A thunderstorm cloud that encompasses the lower, middle and upper levels of the troposphere. They form by a deep
layer of rising positively buoyant air in the troposphere.
There are many unique clouds. Below are several unique clouds that can be seen:
Fractus- Fractus are also known as scud and cloud tags. They are isolated low level stratus clouds that can often be seen around
the base of thunderstorms. They often look unorganized and flow with the low level wind.
Funnel cloud- The cloud produced from condensation from a rotating column of air. The funnel cloud is the visible portion of
a tornado produced from clouds. A funnel cloud is not a tornado if the circulation is not in contact with the ground.
Lenticular- Lenticular clouds are clouds that form above mountains that have a lens and flying saucer shape. They form as
air is lifted to saturation over the top of mountains.
Mammatus- Mammatus are pouched shaped clouds that protrude downward from the thunderstorm's anvil. They form as negatively
buoyant moisture laden air sinks. The cloud remains visible until the air sinks enough that the relative humidity falls below
100%. The portion that has a relative humidity of 100% remains visible. Mammatus tend to be most prominent in extremely
severe storms but can occur when storms are not severe also.
Shelf cloud- A low ominous cloud reaching across the sky in associated with thunderstorm outflow.
Wall cloud- A lowered cloud base within the updraft region of a supercell thunderstorm. The rapid lifting of humid air causes
the cloud base to form at a lower elevation. Wall clouds will often rotate cyclonically.