Brain Pop:

Clouds

Cloud

Types 18.3

18.3 Types of Clouds

•Clouds are classified based

on how they formed and

their height

•3 basic forms…

• Seen in fair weather, but can mean

rain or snow is coming

Cirrus: (= a curl of hair)

Thin, white, wispy, feathery

• Made from ice crystals at high

altitudes

• Usually mean fair weather

Cumulus: (= a pile)

Rounded, thick, and puffy

masses

• Formed by vertically rising air currents

• Block out sunlight - associated

with rain

Stratus: (= a layer)

Layered, gray, and smooth

• Form in sheets at low altitudes

• 3 levels of height can have seasonal

and latitudinal variation

High Clouds: (above 6000 meters) Cirrus cirrocumulus

cirrostratus

Cirrostratus halo around the sun

Middle Clouds: (2000-6000 meters)

altocumulus

altostratus

Low Clouds: (below 2000 meters)

nimbostratus

Stratus stratocumulus

Clouds of vertical development:

(start at 2000 meters – mid/high)

cumulonimbus

Fog: A cloud with its base at or very near the ground

• The only difference between clouds and fog

is their method and place of formation.

Fogs caused by cooling

Ex: coastal California

• Fog forms when warm

oceanic air moves

over a cold water

current, then wind

blows it over land

• OR fog forms over

land as air temperature

near the ground drops

overnight and reaches

the dew point in the

early morning

• Fog forms over water when water

temperatures are still warm, but air

temperatures have fallen rapidly

• Ex: Fall and early winter

Fogs caused by evaporation

Brain Pop:

Snowflakes

Brain Pop:

Rainbows

Precipitation 18.3

How Precipitation Forms • Cloud droplets = < 20 micrometers. They

must grow in volume by roughly 1 million

times for precipitation to form.

Cold Cloud Precipitation • Bergeron Process: Theory that relates the

formation of precipitation to two physical

processes – supercooling and supersaturation

• Supercooled water: the condition of water droplets

that remain in the liquid state at temperatures well

below 0oC

• Supersaturated air: the condition of air that is more

highly concentrated than normally possible relative

humidity is > 100%

• Water will freeze if it comes in contact with a

solid object (freezing nuclei)

• Collision-

Coalescence

Process: Theory that

says large cloud

droplets collide and

join together with

smaller droplets to

form a raindrop.

Opposite electrical

charges may bind the

cloud droplets

together.

Warm Cloud Precipitation

Forms of Precipitation • The type of precipitation that reaches Earth’s

surface depends on the temperature profile

in the lowest few kilometers of the

atmosphere

Drizzle: < 0.5

mm in diameter.

Fall slowly &

close together

Rain: >0.5 mm in diameter.

Fall faster & farther apart

• Air temp < -5oC & air is drier light fluffy snow

• Air temp > -5oC & air is wetter

thick clumps of snow

Snow: six-sided ice crystals

Sleet: When a layer

of freezing air

overlies subfreezing

air near the ground,

small particles of ice

fall.

Glaze: When raindrops become

supercooled (below 0oC) as they fall, then

turn to ice on impact. A.K.A. freezing rain.

Hail: Ice pellets formed

in cumulonimbus clouds.

Form layers of ice if

carried upward by a

strong updraft.

• rain gauge: Instrument used to

measure the amount of rainfall