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Cloud Types
• Recognizing and appreciating Nature’s
water carriers
Convection: How Clouds Form
Upward flowing air
currents cause
clouds to form
Warm air
condenses in
higher cool air
Warm air rises
Different Heights, Different Clouds
High Level: Cirrus
• Forms only in very dry air
• May mean fine weather will
continue
• If cirrus increases to cover
most of the sky, wind and rain
may soon follow
• Cirrus is made up of falling ice
crystals drawn out by the wind
into filaments
• The longer the filaments, the
stronger the wind
• Sailors once used cirrus
clouds as a "wind warning"
High Level: Cirrocumulus
• A patch or layer of cloud
consisting of tiny individual
cloudlets at high level
• The cloudlets may make a
regular dappled or rippled
pattern
• Referred to as a "mackerel"
sky
• May mean unsettled weather is
on its way
• Like all high-level clouds,
cirrocumulus is made of ice
crystals
Cirrostratus
• May cover the sky as a
continuous sheet with no
features, but it often has a
fibrous look
• Cloud is so thin it is almost
transparent
• You can see the sun or moon
through it
• Forms a halo around sun or
moon
• Cirrostratus often signals
changing weather
Medium Level: Nimbostratus
• Blanket of grey cloud hiding
the sun and any higher cloud
• Sheet cloud from which rain or
snow is falling
• Forms when warm, moist air is
lifted steadily over a large area
• Thick enough to block out the
sun
• Base can be quite low:
anywhere from 2,000-7,000 ft
(600-2,000 m)
• Usually the air is stable and
there is little turbulence in the
cloud
Medium Level: Altostratus
• From the ground altostratus
looks white or slightly blue and
watery
• May form a continuous sheet,
or look as though it is made
from soft fibres
• Light, with the sun often visible
through it
• Rain or snow may fall.
• Frequently, though not always,
covers the whole sky
• Clouds of other types may be
visible at its edges or beneath
it
Medium Level: Altocumulus
• Small, white, puffy clouds that
sometimes slowly drift across
the sky
• Looks like dozens, of small,
loose cotton balls
• Forms between 8,000-18,000
ft (2.5-5.5 km)
• Usually forms in a layer of
moist air, where air currents
undulate gently
• As a layer rises, water vapour
condenses, forming the cloud
Low Level: Cumulus
• Puffy white clouds that drift
across the sky on a bright
summer day
• Small and scattered, they’re a
sign of fine weather
• Clouds form in columns of
rising air above ground that is
being heated strongly by the
sun
• As it rises it cools, and the
water vapour condenses onto
particles of matter called
condensation nuclei
Low Level: Stratus
• Forms in stable air, which has
little or no turbulence
• If it forms in air lifting over hills
or along a front, it may be
followed by rain
• Can also form at night when
moist air moves over land that
is cooling
• Base height is normally in the
lowest 2,000 ft (600 m) of the
atmosphere
Low Level: Stratocumulus
• Grey, white, or a mixture of
both, usually with some darker
patches
• Can look threatening, but
unless it’s very thick usually
only drizzle or light rain falls
from it
• Formed when warm, moist air
mixes with drier, cooler air and
the mixture is moving beneath
warmer, lighter air above
• Base is typically at 1,0007,000 ft (300-2,000 m)