Home Meteorology Weather Predicting Weather Instruments Phenomena Cloud Chart

 

Look up in the sky. What kind of clouds do you see? Clouds are made up of liquid water or ice crystals, and the water droplets or particles are not large or heavy enough to fall to the ground. Fog is also made up of liquid water and can be called a "cloud on the ground." Clouds provide one of the keys to understanding the weather. Knowing about clouds, their shapes and changing patterns, will help you forecast weather changes. Clouds form when the air is cooled when the air is "lifted" by: Winds forcing it up a slope such as a mountain, when two air masses meet along a front or by convection resulting from unequal heating of the surface below.

At the higher altitudes the air expands and cools causing water vapour contained in the air to condense into tiny but visible water droplets. If the droplets grow large enough they form raindrops and fall to the ground.

In general, different kinds of clouds indicate different kinds of weather.

                            Low Clouds - Under 10,000 Feet

Cumulus clouds -

Cumulus is Latin for heap. Cumulus clouds are usually associated with fair weather, but can produce precipitation if they are very tall. When large and bunched, they can cause heavy showers, especially in warm weather.

Stratus clouds -

Stratus is the Latin word for layer or blanket. Stratus clouds form a low layer that can cover the entire sky like a blanket. Rain and drizzle often come from stratus clouds. If they lift quickly in the morning, they often indicate a fine day ahead.

Nimbostratus Clouds -

Nimbostratus clouds are dark sheets of clouds which blot out the sun and are often followed by lengthy precipitation within a few hours.

Stratocumulus Clouds -

Stratocumulus clouds are low, rolling mass of thin, lumpy grey to white clouds. They may produce light precipitation but usually dissipate by the end of the day.

Middle Clouds - 10,000 to 20,000 Feet

Altocumulus Clouds -

Altocumulus clouds are larger than cirrocumulus clouds and, they are patterned white to grey clouds that are often rippled or appear in waves. Considered fair weather clouds, they often follow storms.

Altostratus Clouds -

Altostratus clouds are formless grey to bluish clouds that form a thin veil over the sun and moon. If the clouds gradually darken and blot out the sun or moon, precipitation will follow.

High Clouds - Over 20,000 Feet

Cirrus clouds -

In Latin, the word cirrus means curl. Cirrus clouds are very high in the atmosphere where the air is very cold. These clouds of ice crystals are usually associated with fair weather, but may sometimes indicate that storms are on their way.

Cirrostratus Clouds -

Cirrostratus clouds are milky, white-veined clouds that produce a halo around the sun or moon. Often called 'bed-sheet' clouds, if they are replaced by cirrostratus clouds it usually means that precipitation will follow.

Cirrocumulus Clouds -

Cirrocumulus clouds appear in layers that look like rippled sand or fish scales. Nicknamed 'mackerel sky,' they are considered an omen of good weather.

Contrail Clouds -

Contrail clouds are thin, high altitude clouds that are formed when moisture released from jet engines turns into ice crystals.

Towering Clouds - Up To 60,000 Feet

Swelling Cumulus Clouds -

Swelling cumulus clouds are flat-bottomed and have growing, cauliflower-like towers. They often form in midday and precede cumulonimbus clouds.

Cumulonimbus Clouds -

Cumulonimbus clouds are towering storm clouds that bring rain, sleet, hail, thunder, lightning and tornadoes. The top of the cloud is often anvil-shaped.