254 seamanship secrets
HIGH-ALTITUDE CLOUDS
The highest clouds appear to be solid
white and are composed entirely of
ice crystals or fl akes.
Cirrus (Ci). These clouds, the highest
of the earth’s visible clouds, resemble
short strokes from a delicate artist’s
brush.
Cirrocumulus (Cc). Mimicking the
scales on a fi sh with their white, mottled
appearance, these clouds are often
referred to as a mackerel sky. Catch
a glimpse of these near sunset for a
stunning display of light and color.
Cirrostratus (Cs). Milky white and
wispy like cirrus, these clouds show
much longer brushstrokes. Sailors
call these mare’s tails, because of the
resemblance. Check the sky throughout
the day and look for thickening: an
indication of stormy weather ahead.
Sheets of cirrostratus often blur the
image of the sun or moon, resulting
in a halo around the body.
MIDDLE-ALTITUDE CLOUDS
Lumpiness marks the first sign of the
middle cloud layers. The reflection
of land casts a gray shadow onto
their bases.
Altocumulus (Ac). These form
long, narrow bands or rolls—like
conveyor belts—lumped together.
The center of each band may appear
slightly darker than its ends.
Altostratus (As). These look like
a cloud sheet covering the sky with
little shape or form. When the sun
or moon shines behind these clouds,
it looks like a light behind a glass
shower door. This often warns that
precipitation lies ahead.LOW-ALTITUDE CLOUDS
These form long rolls, giant towers,
or shapeless forms.
Cumulus (Cu). Sailors tend to
call these cotton balls fair-weather
clouds—and as long as they remain
independent, they usually are. If they
band together and lower, they may
rapidly change to a more formidable
thunderhead.
Stratocumulus (Sc). These “roll”
clouds often form at sunset and foretell
of a fi ne evening with quiet weather.
Spectacular sunsets accompany their
presence. Soon after the sun sets, they
disappear, leaving clear, star-filled
skies in their wake.
Stratus (St). This shapeless wonder
hugs the earth like a cloak, with a
consistent gray color covering its
underbelly. Rarely is the sun or moon
visible, unless the cloud breaks apart.
Stratus may hover less than 1,000 feet
above earth’s surface, making it the
lowest cloud.
Nimbostratus (Ns). These are a gray
sheet cloud accompanied by steady
rain, and often herald the arrival of a
warm front.
Cumulonimbus (Cb). Get ready to
rumble. Though the bases of these
clouds are at low altitude, their tops
may reach 40,000 feet or higher.
Towering thunderheads and anvil tops
sheered off by super-high-velocity
winds mark this wonder of nature.
They fi nally erupt in light, sound, and
hard rain.Cloud Identification