AVIATION WEATHER CLOUDS

CLOUD TYPES Latin Root Translation Example Cumulus cumulating, heap Fair-Weather Cumulus Stratus layer, straight Altostratus Cirrus curl of hair, horse tail Cirrus Nimbus rain Nimbostratus Alto high Altocumulus Pileus 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

Cirrus Clouds thin and wispy 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.

sheet-like and nearly transparent Cirrostratus Clouds sheet-like and nearly transparent 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.

parallel bands or rounded masses Altocumulus Clouds parallel bands or rounded masses Altocumulus may appear as parallel bands (top photograph) or rounded masses (bottom photograph). Typically a portion of an altocumulus cloud is shaded, a characteristic 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.

dark, low-level clouds with precipitation 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.

low, lumpy layer of clouds Stratocumulus Clouds low, lumpy layer of clouds 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

Fair Weather Cumulus Clouds puffy cotton balls floating in the sky 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.

reaching high into the atmosphere Cumulonimbus Clouds reaching high into the atmosphere 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.

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

sagging pouch-like structures 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 unstable air; rough turbulence with some icing lenticular altocumulus very strong turbulence nimbostratus very little turbulence; can pose serious icing problems if temperatures are near or below freezing stratus little or no turbulence; hazardous icing conditions if temperatures are near or below freezing. Fog on ground. stratocumulus some 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

Moon Altostratus Scattered stratus

Cumulonimbus

Towering cumulus Cirrostratus Altocumulus

Roll cloud Cumulonimbus

Altocirrus Cirrus

Altostratus Cumulus Stratus

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

Cirrus Fair-weather cumulus Altostratus

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

Stratocumulus Stratus

Cumulus

Stratocumulus

Thor

Stratus

Fair-weather cumulus Tree

Stratocumulus

Stratus Cumulus Stratocumulus

Cirrocumulus Stratus Stratocumulus

Stratocumulus

Altocumulus and crazy pilot

Stratus Towering cumulus Romantic interlude

See the orthographic build-ups on the far side of the mountain? Which way is the wind blowing? What time of day is it? Afternoon

Stratus

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

Cumulonimbus Stratus Towering cumulus Altostratus

Fair-weather cumulus – looking up from the bottom

Fair-weather cumulus – looking down from the top

Altostratus Stratus Cumulus Crab

Are these Pileus clouds? Cumulonimbus Cumulus

Cirrus

Cirrus

Fair-weather cumulus Altostratus Be careful! Low-flying military aircraft practice here!

Fair-weather cumulus

Stratocumulus

Altostratus Cumulus

Cumulonimbus Cold front WARM AIR Alien COLD AIR See the anvil top? Altostratus Which way is the storm moving? Altocumulus

Cumulus Cirrus Cirrocumulus

Towering cumulus

Stratus Cumulus

TV antenna Altocumulus

Altocumulus Cirrus

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

Cirrus

What direction is the wind blowing?