CLOUDS

* Form of condensation

* Visible chunks of small water droplets or ice crystals

* Good indicators of what’s going on in the atmosphere

Conditions necessary for clouds to form

1. Condensation Nuclei –small, solid particle in the atmosphere that provide a surface that water vapor can condense on. (smoke, dust, ice)

2. Saturated air at its dew point

Convective Cooling (Adiabatic Cooling)

• Air rises and expands.

• This cools the air below the dew point and it condenses.

Forceful Lifting

• Air is forced upward when it hits a slope.

• It rises, expands, cools and condenses into a cloud.

Temperature Change

• Two air masses mix and cool below the dew point and condense.

Classified by form and altitude

Root names:•Cirrus: feathery/fibrous•Stratus: layered•Cumulus: piled up•Alto: middle•Nimbus: rain

Stratus

• Flat base• Very low• Cover large areas• May block sun• Very little precipitation

Nimbostratus

• Large, thick, grey patches

• Block out sun• Continuous rain or snow • Storm clouds

Altostratus

• Thin, gray fibers• Sun shines through• Rain or snow of long duration.

Cumulus

• Fluffy cotton balls• White tops & dark bases. • Fair weather

Altocumulus

• Flat bottomed gray/white • Begin at middle altitude• Possible rain & storms

Stratocumulus

• Low, lumpy layer• Forms as rolls or waves

Cumulonimbus

• Anvil shape at top • Dark base• T-storms & heavy rain/possible hail. Summer clouds.

Cirrus

• Delicate• Wispy, feathery• Tiny ice crystals• Fair weather clouds.

Cirrocumulus

• thin, white rippled layers

• tiny ice crystals• mackerel sky• fair weather• thicken if storm’s coming...

Cirrostratus

• tiny ice crystals• shapeless white veil “milky,”

• do not block sun• rain within 24 hrs

CONTRAILS

KELVIN-HELMHOLTZ: caused by winds being deflected up & over a barrier (such as a mountain), causing a wave-like cloud structure

LENTICULAR: form downwind of an obstacle in the path of a strong air current.

MAMMATUS: sinking air within a cloud

Radiation FogGround cools off at night

Air touching ground becomes cooled to the dew point and condenses

“Burned away by sun as it warms up

Advection Fog

• Warm, moist air moves over a cool surface and forms a thick fog

• Common along coasts

Upslope Fog

• Humid air rises up an incline cools off and condenses into fog.

Steam Fog

• Shallow layer of fog• Forms when cool air moves over inland warm body of water