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Climate | Weather Watching | Avalanches | The Sun
Clouds and Precipitation | Wind 

D. Cloud Descriptions and Helpful Hints for Identification
In 1803 a pharmacist and amateur meteorologist, Luke Howard, developed ten categories for cloud identification that are still used today. His descriptions focus on the way clouds look so with practice, anyone can learn to identify clouds. Each category is a variation on three basic cloud types under different conditions, with particular attention to the altitude and appearance of the cloud.

Basic Cloud Shapes:
Cumulus - heaped and puffy that usually grow upwards as well as outwards.
Stratus - layered and flat with wide coverage.
Cirrus - wispy, feathery tufts of clouds often characterized by curly wisps at the ends; sometimes called 'mares tails' because they look like horse's tails blowing in the wind.

Clouds occur at three altitude ranges (heights) in the sky. We judge the height of the clouds according to the base or bottom of the cloud and not the height (this is especially important for cumulus clouds).

High Altitude Clouds:

  • are above 6000 metres
  • start with 'cirro' or 'cirrus'
  • are either:
    1. Cirrus - 'Cirrus' being wispy and feathery at high altitude.

    2. Cirrocumulus - 'Cumulus' being puffy and heaped; 'Cirro' meaning high altitude. Less puffy than cumulus and more wispy like cirrus, but with definite bumps and ripples. The sun is visible through them.

    3. Cirrostratus - 'Stratus' being flat layers of clouds and 'Cirro" being high altitude; the layers are wispy and form a thin veil of coverage over all or part of the sky through which you can see the sun.

    Middle Altitude Clouds:

  • are between 2000 and 6000 metres
  • start with 'alto'
  • are either:
    4. Altocumulus - 'Cumulus' being puffy and heaped, but less dense in appearance than cumulus in a rippled pattern. There are also more spaces in the clouds so the sun is visible through them.
    5. Altostratus - 'Stratus' being flat layers of formless, shapeless clouds. The sun is visible through this sheet of clouds that can cover part of the sky or the full sky from horizon to horizon.
    NOTE: there are no middle range clouds with the prefix 'cirrus' or 'cirro' because Cirrus clouds are synonymous with high altitude clouds.

    Low Altitude Clouds:

  • are below 2000 metres
  • have no prefix
  • are either:
    6. Stratus - Flat layered clouds, usually dull grey, which cover most of the sky, even blocking out the sun. They begin as a bank of fog that has risen higher than ground level.
    7. Nimbostratus - 'Stratus' meaning broad layers covering the whole sky, and 'Nimbo' meaning that they are producing steady, long lasting, though not heavy, rain that covers a broad area. They are dark grey clouds that usually mean a dull day and possibly rain. They completely block out the sun.
    8. Cumulus - Meaning puffy and heaped.
    9. Stratocumulus - Meaning they are basically a flat sheet of clouds covering most, if not all of the sky, but "cumulus' meaning that the layer is somewhat puffy.
    10. Cumulonimbus - 'Cumulo' meaning puffy, and 'nimbus' meaning there is precipitation falling from them. Characterized by dark bases and puffy tops, heavy rain, and thunder and lightening.

    Any low altitude clouds that are dark, threatening rain or producing rain get the designation 'nimbus' or 'nimbo'.

    Cumulus and Cumulonimbus clouds have a base that starts at less than 2000 metres, but often grow tall enough to reach into the middle and sometimes high ranges. Only cirrus-type clouds are true high altitude clouds. They a base starting above 6000 meters.

    Extended Notes About Cloud Shapes:

    Cumulus means a heap or pile in Latin. These are white puffy clouds that look like giant bunches of cauliflower with flat bottoms. They are seen mainly in the summer on warm, sunny days. The sun warms the ground and huge bubbles of heated air rise into the sky. As with other clouds, the air cools, condenses, and in this case forms a cloud that is big and fluffy looking due to the cloud being formed with liquid versus ice crystals.

    Cumulus clouds reflect sunlight well because of the water droplets and they look very white. They are darker on the bottom because the sunlight gets filtered out more and more as it passes through these thick clouds, especially when they are at their largest. We generally don't see these in winter because it is too cold for the droplets to remain unfrozen.

    Cirrus means a curl or a tuft of hair (wispy) in Latin. These are feathery, wispy clouds with curled tails, like a horse's tail blowing in the wind. These are high-altitude clouds made the same way that all clouds form, but the water droplets are frozen to form millions of tiny ice crystals. They are often the first clouds to appear in a clear, blue sky.

    Stratus means a flat layer or 'stretched out' in Latin. These are dull grey clouds. They cover most of the sky and block out direct views of the sun. They often start as a bank of fog (low dense cloud) that rises higher in the sky.

    How Do Clouds Form?
    For more detail on weather fronts, see the sections:




    Clouds occur at weather fronts. Weather fronts occur where warm and cold air masses meet.

    Warm air is pushed higher and as it rises and cools, this causes condensation, which forms clouds. Clouds, mist and fog are made of millions of water droplets of condensing moisture from the air. They can also be made of tiny ice crystals that form as a result of the cooling process happening more quickly, or to lower surrounding temperatures.

    Rain and snow, as well as freezing rain and hail are variations of the precipitation that falls from clouds depending on the conditions in which they form. The conditions are influenced by the geographic location, weather fronts, climate, season of the year, amount of moisture in the air that results in the daily temperature, and the occurrence, amount, and form of precipitation.

    Fog is a cloud up close. It forms close to the ground as a result of air currents and fronts. A cloud is exactly the same as the white puffs of air that we see when we breathe outside on a cold day. The warm air from our lungs contacts the cold air and condenses into water droplets, forming the visible white cloud of condensed air. The same is true of water vapor (the gas form of water once heated to the boiling point) as it escapes a pot of boiling water. The air in the room is cooler than the temperature in the pot and as the warm vapor hits the cooler air, it cools, condenses and forms what we call steam, which is a cloud.

    The most important factor that must exist to form a cloud is the amount of moisture in the atmosphere. If there is not enough water in the atmosphere then there can be no condensation into tiny droplets that form clouds. The water in the atmosphere comes from oceans, lakes and plants through the water cycle. Water in lakes and oceans evaporates, just as water left in a bowl for a period of time will eventually disappear. Water that plants draw up through their roots eventually evaporates through the leaves of the plants.

    It evaporates, rising as a gas into the atmosphere, but condensing as it begins to cool in higher altitudes to form clouds. The water droplets grow larger as more warm air condenses and eventually become too heavy to continue rising or to be held up by the rising warm air. At this point the water droplets fall in the form of precipitation.

    Forms of Precipitation
    Water is part of a cycle called the Water Cycle. As water evaporates from the various bodies of water, plants, and animals, it rises into the atmosphere. There, some of the water rises high enough to cool at the higher altitude, which causes the water vapor to condense into tiny water droplets that form clouds. Some clouds produce precipitation, during which the water that forms the clouds falls back to the earth.

    Precipitation is in different forms depending on the altitude of the cloud. The altitude affects the temperature in the atmosphere and therefore the form of the water droplets that form the clouds. Another influence on the type of precipitation that forms is whether there are strong upward drafts of air inside the cloud.

    Rain is a water droplet in liquid form, usually in lower altitude clouds.

    Snow falls when clouds are in higher and colder altitudes, which causes the water vapor to freeze as it condenses to form ice crystals instead of water droplets that form the cloud.

    Sleet is rain that freezes as it is falling in cold temperatures.

    Freezing Rain is rain that freezes when it contacts the ground.

    Hail forms inside tall clouds with air currents blowing the water droplets up and down. Rain starts to fall inside the cloud, but it is caught by an upward sweeping wind and forced into a higher altitude. The drop of rain freezes in the higher altitude and falls, forming more condensation on it. It can be swept up again to refreeze, forming a larger hailstone. The size of the hailstone depends on the number of times this cycle repeats, which depends on the strength of the upward draft of wind in the cloud.


Climate | Weather Watching | Avalanches | The Sun
Clouds and Precipitation | Wind


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