
.topic 100
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 110
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 120
denotes the conditions which generally exist during precipitation and a short time before and after


.topic 130
Transparent, whitish cloud veil of fibrous (hairlike) or smooth appearance, totally or partly covering the sky, and generally producing halo phenomena.


.topic 140
Detached clouds in the form of white, delicate filaments or white or mostly white patches or narrow bands. These clouds have a fibrous (hair-like) appearance, or a silky sheen, or both.


.topic 150
corona: One or more sequences (seldom more than three) of coloured rings of relatively small diameter, centred on the sun or moon.


.topic 160
Heavy and dense cloud , with a considerable vertical 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 cloud 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 170
Detached clouds, generally dense and with sharp outlines, developing verically in the form of rising mounds, domes or towers, of which the bulging upper part often resembles a cauliflower. The sunlit parts of these clouds are mostly brilliant white; their base is relatively dark and nearly horizontal. Sometimes Cumulus is ragged.


.topic 180
Fairly uniform precipitation composed exclusively of fine drops of water (diameter less than 0.5 mm), very close to one other.


.topic 190
Clouds in the form of irregular shreds, which have a clearly ragged appearance


.topic 200
Precipitation of small balls or pieces of ice (hailstones) with a diameter ranging from 5 to 50 mm or sometimes more, falling either separately or agglomerated into irregular lumps

.topic 210
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 220
A fall of unbranched ice crystals, in the form of needles, column's or plates, often so tiny that they seem to be suspended in the air. These crystals may fall from a cloud or from a cloudless sky.


.topic 230
A luminous manifestation accompanying a sudden electrical discharge which takes place from or inside a cloud or, less often, from high structures on the ground or from mountains.


.topic 240
Grey cloud layer, often dark, the appearance of which is rendered diffuse by more or less continuously falling rain or snow, which in most cases reaches the ground. It is thick enough throughout to blot out the sun. Low, ragged clouds frequently occur below the layer, with which they may or may not merge.



.topic 250
Ragged shreds sometimes constituting a continuous layer, situated below another cloud and sometimes attached to it


.topic 260
Precipitation of very small white opaque grains of ice. These grains are fairly flat or elongated; their diameter is generally less than 1 mm.


.topic 270
Grey or whitish, or both grey and whitish, patch, sheet or layer of cloud which almost always has dark parts, composed of tessellations, rounded masses, rolls, etc., which are non-fibrous (except for virga) and which may or may be not be merged; most of the regularly arranged small elements have an apparent width of more than five degrees.


.topic 280
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.


.topic 290
(a) Start from the box at the top of the diagram and follow one of the two lines leading out of this box.

(b) Proceed from box to box as long as all successive boxes contain criteria which are applicable to the observed sky.

(c) When this procedure leads to a box with a criterion which is not applicable to the observed sky, go back to this previous box and follow the other line leading out of this box.

(d) If this line leads to a box, repeat the procedure described under (b) and (c). If the line leads to a picture, the code figure below this picture is the correct code to be reported.

(e) If all the successive boxes contain criteria which are applicable to the observed sky, the procedure will finally lead to a box from which two or more lines terminate in pictures. Read the citeria below these pictures to obtain the correct code figure.


.topic 300
A sharp or rumbling sound which accompanies lightning

.topic 310
Vertical or inclined trails of precipitation (fallstreaks) attached to the under surface of a cloud, which do not reach the earth's surface

