SYNOP CODE
WW=00-49 No precipitation at the station* at the time of observation
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 Cloud development not observed or observable }characteristic
01 Clouds dissolving or becoming less developed }state of sky
02 State of sky on the whole unchanged }during the
03 Clouds generally forming or developing }past hour
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 } less than 2 m on land or 10 m at sea
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 tuba1 } 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 Drizzle (not freezing) or snow grains }
21 Rain (not freezing) } Not
22 Snow } falling
23 Rain and snow or ice pellets } as shower(s)
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 or { has decreased during the preceding hour
31 }moderate duststorm { no appreciable change during the preceding hour
32 }or sandstorm { has begun or increased during the preceding hour
33 }Severe { has decreased during the preceding
34 }duststorm { no appreciable change during the preceding hour
35 }or 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
43 Fog or ice fog, sky obscured } 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
47 Fog or ice fog, sky obscured } 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
51 Drizzle, not freezing, continuous } of observation
52 Drizzle, not freezing, intermittent } moderate at time
53 Drizzle, not freezing, continuous } of observation
54 Drizzle, not freezing, intermittent } heavy (dense) at time
55 Drizzle, not freezing, continuous } 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
61 Rain, not freezing, continuous } of observation
62 Rain, not freezing, intermittent } Moderate at time
63 Rain, not freezing, continuous } of observation
64 Rain, not freezing, intermittent } Heavy at time
65 Rain, not freezing, continuous } 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
71 Continuous fall of snowflakes } of observation
72 Intermittent fall of snowflakes } moderate at time
73 Continuous fall of snowflakes } of observation
74 Intermittent fall of snowflakes } heavy at time
75 Continuous fall of snowflakes } 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 hail2 at time of observation
94 Moderate or heavy snow, or rain and snow mixed, or hail1
at time of observation
WW=95-99 Thunderstorm at time of observation
95 Thunderstorm, slight or moderate, without hail2 but
with rain and or snow at time of observation
96 Thunderstorm, slight or moderate, with hail2
at time of observation
97 Thunderstorm, heavy, without hail2 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 hail2 at time of observation
* The expression at the station refers to a land station or a ship 1 Tornado cloud or waterspout 2 Hail, small hail, snow pellets
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Last Updated: 7th November 1997
Dave Wheeler weatherman@zetnet.co.uk
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