Climate versus Weather

Climate refers to all weather conditions for a given location over a period of time. The term weather refers to the state of the atmosphere over short periods of time. Weather can change from hour to hour, from clay to day, from month to month, or even from year to year. For periods of 30 years or more, however, meteorological records reveal that distinct weather conditions prevail over different parts of the world. Each set of conditions forms a climate type, and the area covered by a particular type is called a climate region. 

Visit a Gallery of Clouds:

Clouds form when air cools below its dew point. The dew point is the temperature at which air becomes saturated, or filled, with moisture. Although clouds can differ greatly in size, shape, and color, they all consist of visible masses of tiny water droplets or ice crystals, because its capacity to hold water is limited,  very much like a sponge. (photo from Nat. Geogr. Soc.). Warm air can hold more water vapor than cold air can, and lowering the temperature of a mass of air is like squeezing a sponge, moist air becomes cloudy with only slight cooling, whereas dry air must be cooled more to form clouds. 

With further cooling or additional moisture, the ice or water particles that make up clouds can grow together into bigger particles that fall to earth as precipitation. Although the liquid water and the Ice are clear, clouds look white because the droplets and crystals scatter sunlight, When clouds block the sun, they appear gray or black. Water droplets in clouds are microscopic, averaging .01 millimeter (.0004 in) in diameter. Raindrops, which form from droplets, range from less than 5 millimeters (0.2 In) to less than 1 millimeter (.04 in) in diameter and contain millions of times more water. 

FOR EXTRA CREDIT: Study the pictures of the clouds shown here. Classify the clouds and send you result to Prof. Longoria in a separate e-mail.

A Classification of Clouds

Following the classification of clouds originally proposed by Luke Howard, there are three main types of clouds: cirrus, stratus, and cumulus.

Cirriform: Clouds composed of small particles, mostly ice crystals. Because the particles are fairly widely dispersed, this usually results in relative transparency and whiteness, often producing a halo phenomena not observed in other clouds forms. These clouds generally have bases above 20,000 feet in the mid-latitudes, and are classified as high clouds. They include all varieties of cirrus, cirrocumulus, and cirrostratus clouds. 
Cirrus clouds (CIRRUS)  One of the three basic cloud forms (the others are cumulus and stratus). It is also one of the three high cloud types. Cirrus are thin, wispy clouds composed of ice crystals and often appear as veil patches or strands. In the mid-latitudes, cloud bases are usually found between 20,000 to 30,000 feet, and it is the highest cloud that forms in the sky, except for the tops, or anvils, of cumulonimbus, which occasionally build to excessive heights. The prefixcirro- refers to clouds that lie more than 6 kilometers (20,000 ft) above the earth, such as cirrocumulus and cirrostratus clouds.<move up>

Cirrocumulus: A cirriform cloud with vertical development, appearing as a thin sheet of small white puffs which give it a rippled effect. It often creates a "mackerel sky", since the ripples may look like fish scales. Sometimes it is confused with altocumulus, however, it has smaller individual masses and does not cast a shadow on other elements. It is also the least common cloud type, often forming from cirrus or cirrostratus, with which it is associated in the sky. 

Cirrostratus: A cirriform cloud that develops from cirrus spreading out into a thin layer, creating a flat sheetlike appearance. It can give the sky a slightly milky or veiled look. When viewed from the surface of the earth, these ice crystals can create a halo effect around the sun or moon. This cloud is a good precursor of precipitation, indicating it may occur within 12 to 24 hours. 

Stratus clouds are stratified, or layered, often blanketing the entire sky with a uniform cover. Clouds in the stratus group often form at the boundary of a warm front. Warm, moist air is forced up over cold air, producing clouds across the entire front. Stratus clouds form when stable air does not permit cumulus ones to develop. They often blanket the sky as a gray layer stretching from horizon to horizon and can measure hundreds of kilometers in length and width. If precipitation falls from these clouds at all, it is usually in the form of drizzle or light snow. <move up>

Cumulus clouds are lumpy or heaped. The weather they bring depends on their height and size. Puffy cumulus clouds form when thermals, up drafts of warm air, cool as they rise to altitudes of about 1 kilometer (3,300 ft), The higher the clouds are, the drier the atmosphere and the fairer the weather will be. <move up

Alto- denotes clouds whose bases are between 2 and 6 kilometers (6,500-20,000 ft) above the earth, such as altocumulus and altostratus clouds. <move up>

Clouds that produce rain take the prefix nimbo- or the suffix -nimbus, as in nimbostratus or cumulonimbusNimbostratus clouds bring continuous precipitation that can last for many hours.
These clouds exhibit a combination of rain or snow, and sometimes the base of the cloud cannot be seen because of the heaviness of precipitation. They are generally associated with fall and winter conditions, but can occur during any season. 
Cumulus clouds can grow into cumulonimbus clouds, or thunderheads, by mid afternoon. Such cumulonimbus clouds also occur along cold fronts. As evening approaches, cumulonimbus clouds usually shrink and gradually become stratocumulus clouds, which rarely produce rain. <move up>

Cloud Seeding - any technique carried out to introduce artificial substances into the cloud with the intent of altering the natural development of that cloud. <move up>


Weather Principles:
Alti Alto
Cloud Seeding
Moisture in the Air
Types of Precipitation



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