• A cloud is a visible aggregate of tiny water droplets and/or ice crystals suspended in the atmosphere

• They can exist in a variety of shapes and sizes. • Some clouds are accompanied by precipitation; rain,

snow, hail, sleet, even freezing rain.

CLOUDS:

Condensation Nuclei

• Tiny particles (dust, salt) which stimulate droplet formation

• Water is known to exist in three different states; as a solid, liquid or gas.

• Clouds, snow, and rain are all made of up of some form of water.

• A cloud is comprised of tiny water droplets and/or ice crystals

• A snowflake is an aggregate of many ice crystals

• Rain is just liquid water.

• Water existing as a gas is called water vapor.

• When referring to the amount of moisture in the air, we are actually referring to the amount of water vapor.

• If the air is described as "moist", that means the air contains large amounts of water vapor.

• Common sources of moisture are the Maritime Air masses.

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• A cloud naming system was invented in 1802 by Luke Howard.

• Clouds are classified into a system that uses Latin words to describe the appearance of clouds as seen by an observer on the ground.

• The table below summarizes the four principal components of this classification system

Latin Root Translation Example

cumulus stratuscirrusnimbus

heap layercurl of hairrain

fair weather cumulus altostratuscirruscumulonimbus

Classifying Clouds

• Clouds are classified according to their form and altitude.

The three main forms: stratus clouds, cumulus clouds and cirrus clouds.

The three altitude groups:

low clouds (up to 2000m)

middle clouds (2000 – 6000m)

high clouds (above 6000m)

Stratus Clouds- flattened, layered shape - cover large areas of sky- usually form when a warm air mass overruns a cold

air mass- indicate stable conditions

Cumulus Clouds - puffy, “heaped” shape- created by convective or frontal cloud formation- usually indicate unstable weather

Cirrus Clouds- thin, wispy clouds- the highest clouds in the sky- created by wind blown ice crystals- usually indicate fair weather

• One more cloud sub-classification is the word nimbus indicating a rain carrying cloud

Alto = mid-level cloud

High-Level Clouds • Cirrus - high-level clouds

form above (6,000 meters) and since the temperatures are so cold at such high elevations, these clouds are primarily composed of ice crystals. High-level clouds are typically thin and white in appearance. They move across the sky on bright sunny days. Cirrus clouds mean warm air is on the way.

Cirrus - high-level clouds

Mid-Level Clouds • The bases of mid-level

clouds typically appear between 2,000 to 6,000 metres. Alto- clouds, because of their lower altitudes, are composed primarily of water droplets, they can also be composed of ice crystals when cold enough.

                                     

Altocumulus Clouds

parallel bands or rounded masses

Low-level Clouds • Low clouds are

mostly composed of water droplets since their bases generally lie below 2,000 meters. When cold enough, these clouds may also contain ice particles and snow. Nearly all low clouds are some form of stratus cloud.

Nimbostratus Clouds

dark, low-level clouds with precipitation

Stratus Clouds

Fair Weather Cumulus Clouds puffy cotton balls floating in the sky

• Fair weather cumulus have the appearance of floating cotton with flat bases have a lifetime of 5-40 minutes. The cloud tops designates the limit of the rising air. Given suitable conditions, however, harmless fair weather cumulus can develop into cumulonimbus clouds associated with thunderstorms.

Cumulus Clouds

Classification of Clouds Sheet

Label the diagram with the correct name at the appropriate altitude

Stratus

Stratus

http://images.google.ca/images?q=tbn:IhT6BeU74SwJ:http://www.centennialofflight.gov/2003FF/clues/clipart/stratus.jpg

Stratus

Nimbostratus

Nimbostratus

Cumulus

Cumulus

Cumulus

Stratocumulus

Altocumulus

Altostratus

Cumulonimbus

Base of cloud

Cumulonimbus

Cumulonimbus

http://epod.usra.edu/archive/images/cumulonimbus_052301_sjr.jpg

CirrocumulusCirrostratus

Cirrocumulus

Cirrus

Cirrus

Nimbus

A few interesting clouds………

Mammatus clouds

Form below the anvil of a thunderstorm

Usually seen with storms that produce tornadoes….

Strange Clouds….

UFO?

More “UFO’s”….

Rain or Snow? dependent upon temperature

• Precipitation typically forms high in the atmosphere where the temperature is below freezing. As ice crystals form aloft and fall toward the surface, they collect each other to form large snowflakes. If ground temperature is above 0C, the freezing level must be located somewhere above the ground. As the falling snow passes through the freezing level into the warmer air, the flakes melt and collapse into raindrops. During the summer months, it is not uncommon for the freezing level to be found at a level above cloud base.

0C 0C

• When the air temperature at the ground is less than 0C, the snowflakes do not melt on the way down and therefore reach the ground as snow.

0C 0C

Rain and Hail • Rain develops when

growing cloud droplets become too heavy to remain in the cloud and as a result, fall toward the surface as rain. Rain can also begin as ice crystals that collect each other to form large snowflakes. As the falling snow passes through the freezing level into warmer air, the flakes melt and collapse into rain drops.

• Hail is a large frozen raindrop produced by intense thunderstorms. As the snowflakes fall, liquid water freezes onto them forming ice pellets that will continue to grow as more and more droplets are accumulated. Upon reaching the bottom of the cloud, some of the ice pellets are carried by the updraft back up to the top of the storm where they will repeat the growth steps. When the stones are too heavy for the updraft, the stones fall.

Freezing Rain • Ice storms can be the most

devastating of winter weather phenomena and are often the cause of automobile accidents, power outages and personal injury. Ice storms result from the accumulation of freezing rain, which is rain that becomes supercooled and freezes upon impact with cold surfaces.

• Freezing rain develops as falling snow encounters a layer of warm air deep enough for the snow to completely melt and become rain. As the rain continues to fall, it passes through a thin layer of cold air just above the surface and cools to a temperature below freezing. The drops do not freeze, a phenomena called supercooling occurs ("supercooled drops“ form). When the supercooled drops strike the frozen ground (power lines, or tree branches), they instantly freeze, forming a thin film of ice, hence freezing rain.

Snow • Snowflakes are simply aggregates of ice crystals that collect to each other as they fall toward the surface. The diagram shows a typical temperature profile for snow with the red line indicating the atmosphere's temperature at any given altitude. The vertical line in the center of the diagram is the freezing line. Temperatures to the left of this line are below freezing, temperatures to the right are above freezing. Since the snowflakes do not pass through a layer of air warm enough to cause them to melt, they remain in tact and reach the ground as snow.