
.topic 10
White or grey, or both white and grey, patch, sheet or layer of cloud, generally with shading, composed of laminae, rounded masses, rolls, etc., which are sometimes partly fibrous or diffuse and which may or may not he merged; most of the regularly arranged small elements usually have an apparent width between one and five degrees.


.topic 20
Greyish or bluish cloud sheet or layer of striated, fibrous or uniform appearance, totally or partly covering the sky, and having parts thin enough to reveal the sun at least vaguely, as through ground glass. Altostratus does not show halo phenomena.

.topic 30
Thin, white patch, sheet or layer of cloud without shading, composed of very small elements in the form of grains, ripples, etc., merged or separate, and more or less rgularly arranged; most of the elements have an apparent width of less than one degree.


.topic 40
Transparent whitish cloud veil of fibrous (hair-like) or smooth appearance, totally or partly covering the sky, and generally producing halo phenomena.


.topic 50
Detached clouds in the form of white, delicate filaments or white or almost white patches or narrow bands. These clouds have a fibrous (hair-like) appearance, or a silky sheen, or both.

.topic 60
Heavy and dense cloud , with a considerablevertical extent, in the form of a mountain or huge towers. At least part of its upper portion is usually smooth, or fibrous or striated, and nearly always flattened; this part often spreads out in the shape of an anvil or vast plume. Under the base of this c;oud which is often very dark, there are frequently low ragged clouds either merged with it or not, and precipitation sometimes in the form of virga.


.topic 70
An optical phenomenon in the form of a ring, arc, pillar or bright spot, produced by the refraction of light by ice crystals suspened in the atmosphere (cirriform clouds, ice fog, etc.). This phenomenon, when formed by refraction of the light of the sun, may show colors, while a halo phenomenon produced by the light of the moon is always white.


.topic 80
A suspension in the air of extremely small, dry particles invisible to the naked eye and sufficiently numerous to give the air an opalescent appearance.


.topic 90
Generally grey cloud layer with a fairly uniform base, which may give drizzle, ice prisms or snow grains. When the sun is visible through the cloud, its outline is clearly discernible. Stratus does not produce halo phenomena except, possibly, at very low temperatures. Sometimes Stratus appears in the form of ragged patches.



