AVIATION WEATHER

CLOUDS

CLOUD TYPESLatin Root Translation Example

Cumulus cumulating, heap Fair-Weather CumulusStratus layer, straight AltostratusCirrus curl of hair, horse tail CirrusNimbus rain NimbostratusAlto high AltocumulusPileus Skull cap Smooth tops

High-level clouds=20,000 feet and higher, cirrus, cirrostratus, cirrocumulus

Mid-level clouds=6,500 to 20,000 feet, altostratus, altocumulus, cumulonimbus

Low-level clouds=clouds below 6,500 feet, stratus, stratocumulus

Clouds with vertical development

The most common form of high-level clouds are thin and often wispy cirrus clouds. Typically found at heights greater than 20,000 feet, cirrus clouds are composed of ice crystals that originate from the freezing of super-cooled water droplets. Cirrus generally occur in fair weather and point in the direction of air movement at their elevation.

Cirrus Clouds thin and wispy

Sometimes the only indication of their presence is given by an observed halo around the sun or moon. Halos result from the refraction of light by the cloud's ice crystals. Cirrostratus clouds, however, tend to thicken as a warm front approaches, signifying an increased production of ice crystals. As a result, the halo gradually disappears and the sun (or moon) becomes less visible.

Cirrostratus Clouds sheet-like and nearly transparent

Altocumulus may appear as parallel bands (top photograph) or rounded masses (bottom photograph). Typically a portion of an altocumulus cloud is shaded, acharacteristic which makes them distinguishable from the high-level cirrocumulus. Altocumulus clouds usually form by convection in an unstable layer aloft, which may result from the gradual lifting of air in advance of a cold front. The presence of altocumulus clouds on a warm and humid summer morning is commonly followed by thunderstorms later in the day.

Altocumulus Clouds parallel bands or rounded masses

Nimbostratus Clouds dark, low-level clouds with

precipitation

Nimbostratus are dark, low-level clouds accompanied by light to moderately falling precipitation. Low clouds are primarily composed of water droplets since their bases generally lie below 6,500 feet. However, when temperatures are cold enough, these clouds may also contain ice particles and snow.

Stratocumulus clouds generally appear as a low, lumpy layer of clouds that is sometimes accompanied by weak intensity precipitation. Stratocumulus vary in color from dark gray to light gray and may appear as rounded masses, rolls, etc., with breaks of clear sky in between

Stratocumulus Clouds low, lumpy layer of clouds

Fair weather cumulus are fueled by buoyant bubbles of air, or thermals, that rise upward from the earth's surface. As they rise, the water vapor within cools and condenses forming cloud droplets. Young fair weather cumulus have sharply defined edges and bases while the edges of older clouds appear more ragged, an artifact of cloud erosion. Evaporation along the cloud edges cools the surrounding air, making it heavier and producing sinking motion (or subsidence) outside the cloud.

Fair Weather Cumulus Clouds puffy cotton balls floating in the sky

Lower levels of cumulonimbus clouds consist mostly of water droplets while at higher elevations, where temperatures are well below 0 degrees Celsius, ice crystals dominate. Under favorable atmospheric conditions, harmless fair weather cumulus clouds can quickly develop into large cumulonimbus clouds associated with powerful thunderstorms known as super cells.

Cumulonimbus Clouds reaching high into the atmosphere

Billow clouds are created from instability associated with air flows having marked vertical shear and weak thermal stratification. The common name for this instabilityis Kelvin-Helmholtz instability. These instabilities are often visualized as a row of horizontal eddies aligned within this layer of vertical shear.

Billow Clouds produced by Kelvin-Helmholtz instability

Mammatus Clouds sagging pouch-like structures

Sometimes very ominous in appearance, mammatus clouds are harmless and do not mean that a tornado is about to form; a commonly held misconception. In fact, mammatus are usually seen after the worst of a thunderstorm has passed.

Pileus Clouds smooth capping clouds

Pileus (Latin for "skullcap") is a smooth cloud found attached to either a mountain top or growing cumulus tower.

Cloud Type Effects on Flight

cirrus no significant icing; turbulence in dense, banded cirrus

cirrocumulus supercooled water droplets = some turbulence and icing

cirrostratus little if any icing; no turbulence; restricted visibility

altocumulus small amounts of icing; some turbulence

altostratus moderate amounts of icing; little turbulence; restricted sunlight

altocumulus unstable air; rough turbulence with some icing

lenticular altocumulus

very strong turbulence

nimbostratusvery little turbulence; can pose serious icing problems if temperatures are near or below freezing

stratuslittle or no turbulence; hazardous icing conditions if temperatures are near or below freezing. Fog on ground.

stratocumulussome turbulence; possible icing at subfreezing temperatures; ceiling and visibility better than with low stratus clouds

cumulus sunstable air will give some turbulence, but no significant icing

towering cumulus

strong turbulence,rain showers; clear icing above freezing level

cumulonimbus unstable air; violent turbulence; strong possibility for icing                    

CLOUD IDENTIFICATION TEST

Cirrus

Fair Weather Cumulus

Stratus

Nimbostratus Stratus Virga

Towering cumulus

Lenticulars

Fair-weather cumulus

Altocumulus

Cumulonimbus

Stratocumulus

Cumulonimbus

Mammantus

Mammantus

Altostratus Scattered stratus

Moon

Cumulonimbus

Towering cumulus Cirrostratus Altocumulus

CumulonimbusRoll cloud

Cirrus Altocirrus

CumulusAltostratus

Stratus

Which way is the wind blowing? What time of day is it?

Evening

Fair-weather cumulus Cirrus Altostratus

Is there a light wind? Yes Which way is it blowing?

Advection fog Upslope fog

StratusStratocumulus

Cumulus

Stratocumulus

Thor

Stratus

Fair-weather cumulus

Tree

Stratocumulus

Stratus Cumulus

Stratocumulus

CirrocumulusStratocumulus Stratus

Stratocumulus

Altocumulus and crazy pilot

Stratus Towering cumulus

Romantic interlude

Which way is the wind blowing?

What time of day is it? Afternoon

See the orthographic build-ups on the far side of the mountain?

Stratus

Cumulus Bristlecone pine – lives longer than 2000 years.This particular Bristlecone may have been livingduring the life of Christ!

StratusCumulonimbus Towering cumulusAltostratus

Fair-weather cumulus – looking up from the bottom

Fair-weather cumulus – looking down from the top

Cumulus

AltostratusStratus

Crab

Cumulonimbus Cumulus

Are these Pileus clouds?

Cirrus

Cirrus

Fair-weather cumulus Altostratus

Be careful! Low-flying military aircraft practice here!

Fair-weather cumulus

Stratocumulus

CumulusAltostratus

Cold frontCumulonimbus

Altocumulus Which way is the storm moving?

See the anvil top?Altostratus

Alien

COLD AIR

WARM AIR

Cumulus Cirrus Cirrocumulus

Towering cumulus

CumulusStratus

AltocumulusTV antenna

Cirrus Altocumulus

Towering cumulusStratus

The leading edge of a cold front. Aircraft avoid these things!

Cirrus

What direction is the wind blowing?