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WW=00-19 No precipitation, fog, (except for 11 and 12), duststorm, sandstorm, drifting or blowing snow at the station at the time of observation or, except for 09 and 17, during the preceeding hour

-- 00 - 04: characteristic state of the sky during the past hour
00 Cloud development not observed or observable
01 Clouds dissolving or becoming less developed
02 State of sky on the whole unchanged
03 Clouds generally forming or developing
04 Visibility reduced by smoke haze
05 Haze
06 Widespread dust in suspension in the air, not raised by wind at or near the station at the time of observation.
07 Dust or sand raised by the wind at or near the station at the time of the observation, but no well-developed dust whirl(s), and no sandstorm seen: or, in the case of ships, blowing spray at the station
08 Well developed dust whirl(s) or sand whirl(s) seen at or near the station during the preceding hour or at the time of observation, but no duststorm or sandstorm
09 Duststorm or sandstorm within sight at the time of observation, or at the station during the preceding hour
10 Mist
11 Patches of shallow fog or ice fog
12 More or less continuous
13 Lightning visible, no thunder heard
14 Precipitation within sight, not reaching the ground or surface of sea
15 Precipitation within sight, reaching ground or the surface of the sea, but distant, i.e. estimated to be more than 5 km from the station
16 Precipitation within sight, reaching the ground or the surface of the sea, near to, but not at the station
17 Thunderstorm, but no precipitation at the time of observation
18 Squalls at or within sight of the station during
19 Funnel cloud(s) or tuba during the preceding hour or at time of observation

WW=20-29 Precipitation, fog, ice fog or thunderstorm at the station during the preceeding hour but not at the time observation

-- 20 - 24: Not falling as shower (s)
20 Drizzle (not freezing) or snow grains
21 Rain (not freezing)
22 Snow
23 Rain and snow or ice pellets
24 Freezing drizzle or freezing rain
25 Shower(s) of rain
26 Shower(s) of snow, or of rain and snow
27 Shower(s) of hail, or of rain and hail
28 Fog or ice fog
29 Thunderstorm (with or without precipitation)

WW=30-39 Duststorm, sandstorm, drifting or blowing snow

30 Slight duststorm ( has decreased during the preceding hour )
31 Moderate duststorm ( no appreciable change during the preceding hour)
32 Sandstorm ( has begun or increased during the preceding hour)
33 Severe Sandstorm ( has decreased during the preceding hour)
34 Duststorm ( no appreciable change during the preceding hour)
35 Sandstorm ( has begun or increased during the preceding hour)
36 Slight or moderate drifting snow ( generally low)
37 Heavy drifting snow ( below eye level)
38 Slight or moderate blowing snow ( generally high)
39 Heavy blowing snow ( above eye level)

WW=40-49 Fog or ice fog at the time of observation

40 Fog or ice fog at a distance at the time of observation, but not at the station during the preceding hour, the fog or ice fog extending to a level above that of the observer
41 Fog or ice fog in patches
42 Fog or ice fog, sky visible ( has become thinner during the preceding hour)
43 Fog or ice fog, sky obscured ( has become thinner during the preceding hour)
44 Fog or ice fog, sky visible ( no appreciable change)
45 Fog or ice fog, sky obscured ( during the preceding hour)
46 Fog or ice fog, sky visible ( has begun or has become thicker during the preceding hour)
47 Fog or ice fog, sky obscured ( has begun or has become thicker during the preceding hour)
48 Fog or ice fog, sky visible
49 Fog or ice fog, sky obscured

WW=50-59 Drizzle

50 Drizzle, not freezing, intermittent ( slight at time of observation)
51 Drizzle, not freezing, continuous ( slight at time of observation)
52 Drizzle, not freezing, intermittent ( moderate at time of observation)
53 Drizzle, not freezing, continuous ( moderate at time of observation)
54 Drizzle, not freezing, intermittent ( heavy (dense) at time of observation)
55 Drizzle, not freezing, continuous ( heavy (dense) at time of observation)
56 Drizzle, freezing, slight
57 Drizzle, freezing, moderate or heavy (dense)
58 Drizzle and rain, slight
59 Drizzle and rain, moderate or heavy

WW=60-69 Rain

60 Rain, not freezing, intermittent ( slight at time of observation)
61 Rain, not freezing, continuous ( slight at time of observation)
62 Rain, not freezing, intermittent ( moderate at time of observation)
63 Rain, not freezing, continuous ( moderate at time of observation)
64 Rain, not freezing, intermittent ( heavy at time of observation)
65 Rain, not freezing, continuous ( heavy at time of observation)
66 Rain, freezing, slight
67 Rain, freezing, moderate or heavy
68 Rain or drizzle and snow, slight
69 Rain or drizzle and snow, moderate or heavy

WW=70-79 Solid precipitation not in showers

70 Intermittent fall of snowflakes ( slight at time of observation)
71 Continuous fall of snowflakes ( slight at time of observation)
72 Intermittent fall of snowflakes ( moderate at time of observation)
73 Continuous fall of snowflakes ( moderate at time of observation)
74 Intermittent fall of snowflakes( heavy at time of observation)
75 Continuous fall of snowflakes ( heavy at time of observation)
76 Diamond dust (with or without fog)
77 Snow grains (with or without fog)
78 Isolated star-like snow crystals (with or without fog)
79 Ice pellets

WW=80-99 Showery precipitation, or precipitation with current or recent thunderstorm

80 Rain shower(s), slight
81 Rain shower(s), moderate or heavy
82 Rain shower(s), violent
83 Shower(s) of rain and snow mixed, slight
84 Shower(s) of rain and snow mixed, moderate or heavy
85 Snow shower(s), slight
86 Snow shower(s), moderate or heavy
87 Shower(s) of snow pellets or small hail ( slight )...
88 ...with or without rain or rain and snow mixed ( moderate or heavy)
89 Shower(s) of hail, with or without rain or( slight )...
90 ...rain and snow mixed, not associated with thunder ( moderate or heavy)

WW=91-94 Thunderstorm during the preceeding hour but not at time of observation

91 Slight rain at time of observation
92 Moderate or heavy rain at time of observation
93 Slight snow, or rain and snow mixed, or hail (2) at time of observation
94 Moderate or heavy snow, or rain and snow mixed, or hail (1) at time of observation

WW=95-99 Thunderstorm at time of observation

95 Thunderstorm, slight or moderate, without hail (2) but with rain and or snow at time of observation
96 Thunderstorm, slight or moderate, with hail (2) at time of observation
97 Thunderstorm, heavy, without hail (2) but with rain and or snow at time of observation
98 Thunderstorm combined with duststorm or sandstorm at time of observation
99 Thunderstorm, heavy, with hail (2) at time of observation

(1) Tornado cloud or waterspout
(2) Hail, small hail, snow pellets


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