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<p>A cloud is a hydrometeor consisting of a visible mass made of snow crystals or microscopic water droplets suspended in the atmosphere. Clouds scatter all visible light and that is why they look white. However, sometimes they are too thick or too dense for light to pass through. When this happens, the coloring turns gray or even black. Taking into account that the clouds are water droplets on the atmospheric dust and that they depend on some factors, the drops can turn into rain, hail or snow. They are an aerosol formed by water evaporated mainly from the oceans.</p>
<p> <img src="https://www.meteorologiaenred.com/wp-content/uploads/2012/04/cumulus-humilis.jpg" width="550" height="412"/></p>
<p> <a href="https://www.meteorologiaenred.com/wp-content/uploads/2012/04/cumulus-humilis.jpg">Source</a></p>
<p>The movement of the air associated with the development of clouds also affects their formation. The clouds that are created in the air at rest tend to appear in layers or strata, while those formed between the winds or the air with strong vertical currents present a great vertical development.</p>
<h2>How do clouds form?</h2>
<p>The surface of the earth is covered in 70 percent water. The Sun, heating the seas, rivers, lakes and ponds, causes the evaporation of a large amount of water. At the same time, green plants absorb moisture from the soil and introduce it into the air, through the leaves, in the form of water vapor. This humid, hot air produced on the surface rises into the atmosphere and gradually cools. At a certain point, the aqueous vapor condenses into microscopic droplets.</p>
<p><em><strong>The clouds are constituted</strong></em> precisely by these droplets. Clouds are also formed in other ways: for example, when a mass of hot, humid air rises along the side of a mountain, moisture transforms into clouds.<br>
<em><strong>Clouds can also formed</strong></em> when a mass of hot, humid air rubs a layer of cold air next: hot air cools and condensation occurs.</p>
<p><img src="http://2.bp.blogspot.com/-Wang2G0M1Rw/Ujl-snYYcyI/AAAAAAAAA0I/0s5_3iS7b8g/s1600/formaciones-de-nubes-del-oceno-pacifico-70_1400x900.jpg" width="1323" height="835"/></p>
<p><a href="http://2.bp.blogspot.com/-Wang2G0M1Rw/Ujl-snYYcyI/AAAAAAAAA0I/0s5_3iS7b8g/s1600/formaciones-de-nubes-del-oceno-pacifico-70_1400x900.jpg">Source</a></p>
<p>The clouds are observed with the naked eye and are classified according to an international system created in the early nineteenth century by Luke Howard, an English chemist and meteorologist who divided them into four main categories or forms: <em><strong>high clouds, medium clouds and low clouds.</strong></em> </p>
<h2>High clouds</h2>
<p><em><strong>Cirros: </strong></em>are white clouds, transparent and without internal shadows that have a long and fine filament appearance. These filaments can present a regular distribution in the form of parallel lines, whether straight or sinuous. Occasionally, the filaments have a confusing shape. The general appearance is as if the sky had been covered with brushstrokes. When the cirrus invades the sky it can be estimated that in the next 24 h. there will be a sudden change of time; with decrease in temperature.</p>
<p><em><strong>Cirrocumulus</strong></em>: they form an almost continuous layer that presents the appearance of a surface with fine wrinkles and rounded shapes, like small cotton flakes. These clouds are completely white and have no shadows. When the sky is covered with cirrocumulus, it is often said to be mackerel. Cirrocumulus often appear next to Cirrus and generally indicate a change in climate over the next 12 h. This type of cloud generally precedes storms.<br>
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<em><strong>Cirrostratos:</strong></em> They have the appearance of a veil, being difficult to distinguish the details of the structure, occasionally presenting a long and wide flute. It has defined edges and regular limits. This type of cloud usually produces a halo in the sky around the Sun or the Moon. The Cirrostratos generally pass to the Cirros and prelude the arrival of bad weather by storms or warm fronts.</p>
<p> <img src="https://upload.wikimedia.org/wikipedia/commons/thumb/5/57/Cloud_types_en.svg/450px-Cloud_types_en.svg.png" width="450" height="277"/> </p>
<p> <a href="https://upload.wikimedia.org/wikipedia/commons/thumb/5/57/Cloud_types_en.svg/450px-Cloud_types_en.svg.png"> Source</a></p>
<h2>Average clouds</h2>
<p><em><strong>Altocumulus:</strong></em> They look like medium-sized scales and irregular structure, with shadows between the flakes. They have undulations or wide grooves in their lower part. Altocumulus generally precedes the bad weather produced by rains or storms.</p>
<p><em><strong>Altostratus:</strong></em> thin layers of clouds with some dense areas. In most cases, it is possible to visualize the Sun through the cloud layer. The aspect presented by the Altostratos is that of a uniform layer of clouds with irregular spots. Altostratuses usually presage fine and persistent rain with a drop in temperature.</p>
<p> <img src="http://1.bp.blogspot.com/-f348rY7qv5A/UyDKIBQ1yqI/AAAAAAAAC4g/LDyrf9l63N4/s1600/nubes.jpg" width="646" height="356"/> <a href=""> </a></p>
<p> <a href="http://1.bp.blogspot.com/-f348rY7qv5A/UyDKIBQ1yqI/AAAAAAAAC4g/LDyrf9l63N4/s1600/nubes.jpg"> Source </a></p>
<h2>Low clouds</h2>
<p><em><strong>Nimbostratos:</strong></em> They have the appearance of a regular dark gray layer with different degrees of opacity. With some frequency it is possible to observe a slightly striated appearance that corresponds to different degrees of opacity and variations of gray color. They are typical clouds of spring and summer, rain and snow during the winter.</p>
<p><em><strong>Stratocumulus:</strong></em> They have broad undulations similar to elongated cylinders, and can appear as banks of great extension. These clouds have areas with different intensities of gray. Stratocumulus rarely provides rain, except when they are transformed into Nimbostratus.<br>
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<em><strong>Strata:</strong></em> They have the appearance of a bank of grayish fog without being able to observe a defined or regular structure. They present patches of different degree of opacity and variations of gray coloration. During the autumn and winter, the Strata can remain in the sky all day giving a sad look at the sky. During the spring and early summer, they appear during the morning dispersing during the day, which indicates a good climate.</p>
<p> <img src="http://biglegalbrain.com/cortex/wp-content/uploads/2011/01/cloud_types-300x203.gif" width="300" height="203"/></p>
<p> <a href="http://biglegalbrain.com/cortex/wp-content/uploads/2011/01/cloud_types-300x203.gif">Source</a></p>
<h2>Vertical Development Clouds</h2>
<p><em><strong>Clusters:</strong></em> They have a large size with a massive appearance and very marked shadows when they are between the Sun and the observer, that is, they are gray clouds. They have a horizontal base and on the top large vertical protuberances that deform continuously, presenting an appearance similar to a large cauliflower. The Cumulus corresponds to the good climate when there is little environmental humidity and little vertical movement of air. In the case of high humidity and strong updrafts, Clusters can acquire a large size, causing storms and heavy rains.</p>
<p><em><strong>Cumulonimbus:</strong></em> large size and massive appearance with a very marked vertical development that gives the impression of mountainous cliffs and whose cusp can have the shape of a large fungus; and that presents a smooth or slightly fibrous structure where different intensities of gray or cerulean color are observed. These clouds can have large ice crystals on top. Cumulonimbus clouds are typical of intense storms and can produce hail.</p>
<p><img src="https://www.lakesuperior.com/downloads/2436/download/UCAR_CommonClouds.jpg?cb=1c395f99d00913313d360f5f09392566" width="1240" height="1140"/></p>
<p> <a href="https://www.lakesuperior.com/downloads/2436/download/UCAR_CommonClouds.jpg?cb=1c395f99d00913313d360f5f09392566">Source</a></p>
<p><a href="">https://es.wikipedia.org/wiki/Nube</a></p>
<p><a href="">http://www.astromia.com/tierraluna/nubes.htm</a></p>
<p><a href="">http://www.curiosfera.com/nubes-que-son-formacion-tipos/</a></p>
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