clouds Fine droplets of water or ice crystal suspended in the atmosphere; the World Meteorological Organization classifies them according to 10 types. Fine droplets of water or ice crystal suspended in the atmosphere; the World Meteorological Organization classifies them according to 10 types.

altostratus Gray sheet that can completely cover the sky but allows the Sun to be seen without a halo phenomenon; it can trigger heavy precipitation. Gray sheet that can completely cover the sky but allows the Sun to be seen without a halo phenomenon; it can trigger heavy precipitation.

nimbostratus Cloud in the form of a dark layer sufficiently thick to block out the Sun; it triggers continuous precipitation. Cloud in the form of a dark layer sufficiently thick to block out the Sun; it triggers continuous precipitation.

altocumulus Cloud composed of large white or gray flecks that sometimes form parallel layers; it foreshadows the arrival of a depression. Cloud composed of large white or gray flecks that sometimes form parallel layers; it foreshadows the arrival of a depression.

cirrocumulus Cloud formed of white or gray flecks or strips, often arranged in rows. Cloud formed of white or gray flecks or strips, often arranged in rows.

cirrostratus Whitish layer that can completely cover the sky and that creates a halo around the Sun. Whitish layer that can completely cover the sky and that creates a halo around the Sun.

cirrus Cloud in the form of wisps or separate strips; it usually appears in advance of a depression. Cloud in the form of wisps or separate strips; it usually appears in advance of a depression.

stratus Gray cloud forming a continuous veil that is similar to fog, though it never touches the ground; it can trigger light precipitation. Gray cloud forming a continuous veil that is similar to fog, though it never touches the ground; it can trigger light precipitation.

cumulonimbus Very imposing cloud that can reach a thickness of 6 mi and whose base is very dark; it can trigger violent precipitation. Very imposing cloud that can reach a thickness of 6 mi and whose base is very dark; it can trigger violent precipitation.

cumulus Fair-weather cloud with very clear contours; it has a gray, flat base and a white top with rounded protuberances. Fair-weather cloud with very clear contours; it has a gray, flat base and a white top with rounded protuberances.