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Cloud Characteristics, Continued
Low-Etage
Clouds
Nimbostratus (NS) clouds are a dark gray-colored amorphous
(shapeless) and rainy layer of cloud. They are usually nearly uniform
and feebly illuminated, seemingly from within. When precipitation
occurs, it is in the form of continuous rain or snow, but nimbostratus
may occur without rain or snow. Often there is precipitation that does
not reach the ground, in which case, the base of the cloud may extend
into the low-cloud family.
Stratocumulus (SC) clouds are layer or patches of clouds composed of
globular masses or rolls. The smallest of the regularly arranged
elements are fairly large. They are soft and gray with dark spots.
Stratus (ST) clouds are a low, uniform layer of clouds, resembling fog,
but not resting on the ground. A veil of stratus gives the sky a hazy
appearance. Usually, only drizzle is associated with stratus. When there
is no precipitation, the stratus cloud form appears drier than other
similar forms, and it shows some contrasts and some lighter transparent
parts.
Cumulus (CU) clouds are dense clouds with vertical development.
Their upper surfaces are dome-shaped and exhibit rounded projections,
and their bases are nearly horizontal. Stratocumulus clouds resemble
ragged cumulus clouds in which the different parts show constant
change. Strong updrafts exist under and within larger cumulus
formations. In fact, cumulus clouds, like other forms of vertically
developed clouds, are caused by updrafts.
Cumulonimbus (CB) clouds are heavy masses of cloud, with towering
vertical development, whose cumuliform summits resemble mountains or
towers. Their upper parts leave a fibrous texture, and often they spread
out in the shape of an anvil.
Cumulonimbus clouds are generally associated with showers of rain or
snow, and sometimes produce hail. Thunderstorms are always
associated with cumulonimbus. The bases of the cumulonimbus may be
anywhere from 1,600 feet to 6,500 feet. Although you would rarely see
all types at any one time in nature, quite frequently you may observe
two or three layers of clouds of different types at one observation.
10-9
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