Summer days are approaching, and we visualize long days of sun and blue sky dotted with lazily floating clouds. Ask most people what is the first thing that comes to mind when they hear the word cloud, and they usually report visions of puffy white masses gently floating around; the `ideal clouds’ so often depicted in children’s drawings. As clouds go, these are the friendliest type, gently passing over our heads. There are many types of clouds, and if you get to know the basic types, you can get some insight into what the weather is likely to be.
For the most part, clouds are made up of condensed water vapor. Temperature is also a major factor in cloud formation. Warm air can absorb much more moisture than cold air. That’s why you can see your breath when it’s cold, but not when it is warm. Your breath is a source of moisture, and when the temperature is cold, that moisture readily condenses into little clouds.
Warm moist air will rise, cooling as it goes. Clouds form at the `condensation level,’ that point where the air can no longer hold the water vapor. Now all it takes to have clouds to form, is something for the water vapor to cling to. This is airborne particles of dust, smoke, pollen, salt or volcanic ash. These particles are actually microscopic in size.
Clouds are never still, they are always in motion. Generally, they are moved by the wind, and by rising warm air from the ground heated by the sun. Clouds are classified into ten basic types, and each type generally forms and stays in either the lower, middle or upper atmosphere.
Our `standard cloud’ is a cumulus type cloud. They are low altitude clouds, less than 10,000 feet high. These are often referred to as `fair weather clouds’ because they are rarely associated with precipitation. These clouds often dissipate at night because they are most susceptible to sinking when the air currents cool. They usually do not reach the ground; the water vapor evaporates as it sinks.
The other lower altitude clouds are stratus, and stratocumulus. Stratocumulus are rather ominous looking clouds, usually covering the entire sky with a patchwork effect. Each individual cloud covers the area of an outstretched fist. These clouds may produce a bit of drizzle but are rarely associated with serious precipitation. Stratus clouds are a very low dark uniform gray color. It is a solid blanket of cloud, but it too usually only produces local drizzle.
Middle altitude clouds are found between 10,000 and 20,000 feet. These are the altostratus, altocumulus and nimbostratus clouds. The latter appears as a uniform cloud cover where the sun or moon shine weakly through. Altocumulus clouds are solid patches of small clouds (about the size of an outstretched thumb) with some broken areas. They may produce local rain or snow showers. Nimbostratus clouds are far less friendly than any clouds so far mentioned. These clouds appear as a huge dark gray cloud that covers a large percentage of the sky. Steady `all day’ rains, and heavy snowfall usually follow these portents of bad weather days.
High altitude clouds are found from 20,000 to 50,000 feet. All varieties appear as thin wispy and windblown. Cirrus clouds are thin white swirling clouds, often curling elaborately. Cirrostratus are thin and veil like and are usually the clouds associated with lunar halos. Cirrocumulus clouds produce the `mackerel’ sky appearance. All three types produce no noticeable precipitation, but are usually harbingers of bad weather to follow.
Perhaps the most ominous cloud of all, and the one associated with the most spectacular weather, is the cumulonimbus cloud, that wicked looking thunderhead. This cloud system may range from lower altitude far into the upper atmosphere where it flattens at the top. These clouds may begin forming in the morning and grow to immense proportions by late afternoon. They produce severe thunderstorms, hail, heavy rain, high winds and tornadoes. There is nothing gentle and floating about these clouds!
Clouds can be fascinating to study, and satellite images show cloud patterns on a global basis. Looking at a satellite picture of Earth and its clouds, it may appear as if there is an awful lot of water in the atmosphere. But take heart! If all the clouds were to suddenly dump all the water vapor they hold onto the Earth, it would only produce about an inch of water worldwide, so there is no need to start building an ark,- yet.
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