Transcript High Clouds > 6000 meters

Cloud Terminology
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Cumulus = heap
Stratus = layer
Cirrus = curl of hair
Nimbus = rain
Prefixes Cirr = high ; Alto = mid-level
St: stratus, Sc: stratocumulus, Nb: nimbostratus; Ac: altocumulus, As: altostratus;
Ci: cirrus, Cs: cirrostratus, Cc: cirrocumulus; Cu: cumulus, Cb: cumulonimbus.
High Clouds
> 6000 meters
Cirrus Clouds
thin and wispy
The most common form of high-level clouds are thin and often wispy
cirrus clouds. Typically found at heights greater than 20,000 feet (6,000
meters), cirrus clouds are composed of ice crystals that originate from the
freezing of supercooled water droplets. Cirrus generally occur in fair
weather and point in the direction of air movement at their elevation.
Cirrostratus Clouds sheet-like
and nearly transparent
Cirrostratus are sheet-like, high-level clouds composed of ice crystals.
Though cirrostratus can cover the entire sky and be up to several thousand
feet thick, they are relatively transparent, as the sun or the moon can easily
be seen through them.
Sometimes the only indication
of their presence is given by an
observed halo around the sun
or moon. Halos result from the
refraction of light by the
cloud's ice crystals.
Mid-Level Clouds
2000-6000 meters
Altocumulus Clouds - parallel bands or
rounded masses
Altocumulus may appear as parallel bands
(top photograph) or rounded masses (bottom
photograph). Typically a portion of an
altocumulus cloud is shaded, a characteristic
which makes them distinguishable from the
high-level cirrocumulus. Altocumulus
clouds usually form by convection in an
unstable layer aloft, which may result from
the gradual lifting of air in advance of a cold
front. The presence of altocumulus clouds
on a warm and humid summer morning is
commonly followed by thunderstorms later
in the day.
Altostratus
Altostratus
Altostratus
Low-Level Clouds
< 2000 meters
Nimbostratus Clouds - dark, low-level clouds
with precipitation
Nimbostratus are dark, low-level clouds accompanied by light to moderately falling
precipitation. Low clouds are primarily 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.
Nimbostratus
Stratocumulus Clouds - low, lumpy layer of clouds
Stratocumulus clouds generally appear as a low, lumpy layer of clouds
that is sometimes accompanied by weak intensity precipitation.
Stratocumulus vary in color from dark gray to light gray and may appear
as rounded masses, rolls, etc., with breaks of clear sky in between.
Stratocumulus
Clouds With Vertical
Development
Fair Weather Cumulus Clouds puffy cotton balls
floating in the sky
Fair weather cumulus have the appearance of floating cotton and have a lifetime of
5-40 minutes. Known for their flat bases and distinct outlines, fair weather cumulus
exhibit only slight vertical growth, with the cloud tops designating the limit of the
rising air. Given suitable conditions, however, harmless fair weather cumulus can
later develop into towering cumulonimbus clouds associated with powerful
thunderstorms.
Cumulus
Cumulonimbus Clouds - reaching high into the
atmosphere
Cumulonimbus clouds (Cb) are much larger and more vertically
developed than fair weather cumulus. They can exist as individual
towers or form a line of towers called a squall line. Fueled by
vigorous convective updrafts (sometimes in excess 50 knots), the
tops of cumulonimbus clouds can easily reach 39,000 feet (12,000
meters) or higher.
CumuloNimbus
Fog
Fog – Cloud in contact with the ground