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Weather Guide

Weather has a direct impact on everyone, every day and every hour. In the absence of weather report, we relay on looking at the sky (actually the clouds) to estimate what it would be like in the next little while. Here's some information for arriving at an educated guess (see "Weather and Climate" for more compiicated details).

    Clouds are classified according to shape and altitude (see Figure 01):

  1. Cirrus (curl in Latin) - They are usually thin, white, and feathery. Its presence indicates significant amount of moisture at high altitudes, and serves as a warning that a warm front is on its way, bringing steady rain.
  2. Alto (high in Italian) - These are middle-level clouds. The air at these altitudes is generally stable and without vertical currents. The two principal types are altocumulus (fluffy) and altostratus (layered). Small and temporary altocumulus usually do not associate with an organized weather system or flow of moisture into the area. Only when altocumulus cover a larger area for a longer period of time, then it indicates a more significant source of moisture is present.
  3. Stratus (sheet, layer in Latin) - They are layered and usually gray occurring at medium and low altitudes. Stratus clouds usually yield no precipitation other than drizzle, or light mist. Sometimes they resemble fog, except the clouds are above the ground with the base as low as just above the treetops. There are many variations: opacus nebulosus and opacus uniformis (dark and without features); undulatus (simple linear structure); and translucidus (thin stratus).
  4. Clouds, Types of
  5. Cumulus (pile in Latin) - They are fluffy and lumpy clouds at medium and low altitudes. The presence of cumulus clouds is a sign of fine weather in the region. Shallow, vertical cumulus clouds are made when warm air raised, reaches its dew point, and then condenses. They appear light in color and have flat bases and rounded tops.
  6. Nimbus (cloud in Latin) - Nimbus are rain clouds at low altitudes. Nimbostratus are dark gray to pale blue water-droplet precipitation clouds with noticeable blurring in the area below cloud base (caused by falling precipitation). They occur all year round.
  7. Figure 01 Clouds, Types of
    [view large image]


  8. Cumulonimbus are highly organized clouds make up of water droplets in lower portions, and ice particles in upper reaches, with dark bases and with precipitation falling from them. They carry the thunder storms in the summer. This name is the combo of Cumulo-nimbus meaning "piles of clouds".
Figure 02 below shows the various kinds of weather with different types of clouds.

Figure 02 Weather and Types of Clouds

Figure 03's are taken from an old poster by the title of "A Guide to the Sky" published in 1991.


Figure 03a High Altitude (5 - 13 km) Cirrocumulus and Cirrus clouds for fair weather.


Figure 03b High Altitude (5 - 13 km) Cirrus and Cirrostratus clouds for approaching storm.


Figure 03c Mid-level (2 - 7 km) Altocumulus clouds for approaching storm.


Figure 03d Mid-level (2 - 7 km) Altocumulus, Altostratus, and Nimbostratus clouds from approaching to steady storm.


Figure 03e Low Elevation Stratus, Stratocumulus, and Cumulus clouds progressive to stormy weather.


Figure 03f Low Elevation, towering Cumulonimbus clouds in thunderstorms.



Here's the original poster minus the captions.

Figure 04 Original "A GUIDE TO THE SKY".

Cloud Appreciation As mentioned above, further division is made into types such as cirrostratus and cumulonimbus in order to give a more detailed description of the cloud features. The highest clouds - those of the cirrus group - are composed chiefly of ice crystals. They are thin and wispy, and do not block the sunlight. The layered stratus clouds, on the other hand, tend to be much more dense and usually obscure the Sun. The fluffy, white low-altitude cumulus clouds are associated with good weather (see Figure 05 and hear cloud lyrics). The nimbostratus clouds, which also occur at low altitudes, are rain-bearing clouds. The most spectacular of all cloud formations are the towering cumulonimbus clouds, which develop during thunderstorm activity and rise to great heights.

Figure 05 Summary [view large image]