Clouds
Cloud Formation
 Condensation - water
vapor gathers and forms
water droplets or ice
crystals (deposition)
 1) Warm air rises taking
along vapor, cools and
condenses
 2) Molecules (dust, salt,
ash – condensation nuclei)
combine with water vapor
and form droplets
Where clouds form
 Word parts indicate where
clouds form and describe
appearance
– Strato – layered clouds,
usually form below 6,500 feet
– Cumulo – fluffy clouds that
grow upward
– Alto - between 6,500 and
20,000 feet
– Cirro – feathery clouds
forming above 20,000 feet
– Nimbo – refer to dark rain
clouds
Where clouds form
High Level Clouds
 Bases above 20,000
ft (7,000 m)
 Composed of ice
crystals
 Types: Cirrus,
cirrocumulus,
cirrostratus
High level clouds:
Cirrus Clouds
 Thin, wispy, and
fibrous, hair-like in
appearance
 Indicate fair weather
High level clouds
 Cirrocumulus –
extremely high
– Occur before snowfall,
made entirely of ice
 Cirrostratus –
indicate snow or rain,
blanket sky
– Produce halos around
Sun and moon
Middle level clouds
 Bases between 6,500
and 20,000 ft
 Associated with light
precipitation
 Contain ice crystals
and/or water
droplets
 Types: Altocumulus
and Altostratus
Middle level clouds:
Altocumulus
 Puffy with noticeable
height piling upward
 Commonly followed by
thunderstorms
Middle level clouds:
Altostratus
 More uniform
coverage, still layered
 Gray or bluish in color
 Indicates an
approaching
thunderstorm or
cyclone
Low Level Clouds
 Bases lie below 6,500
ft (2,000 m)
 Mostly water
droplets
 Some ice crystals in
cold climates
 Types: Nimbostratus,
Cumulonimbus,
Stratocumulus,
Stratus, and fog
Low level clouds
 Nimbostratus
– Dark gray, layered
clouds
– Produce steady rain
 Cumulonimbus
– Also low level, but
produce heavy rain,
thunder, lightning, or
hail
Low level clouds: Stratus
Clouds
 Substantial, flat or
layered
 Appear before
thunderstorms, but
produce little
precipitation
 Usually the lowest
 Appear overcast
Low level clouds:
Stratocumulus
 Layers of puffy
clouds, flat on top
 Often cover sky in
winter
 Can produce
precipitation
Low level clouds:
Fog
 “Cloud” that is
touching the ground
 Becomes stratus
when it lifts