EXPLANATION OF SYNOP CODES (FM-12)

AS ISSUED BY MANNED AND AUTOMATED WEATHER STATIONS

Table of Contents

• Surface Observations
  • 000 Group - Identification and Location
  • 111 Group - Land Observations
  • 222 Group - Sea Surface Observations
  • 333 Group - Climatological Data

Syntax

IIiii or IIIII YYGGi 99LLL QLLLL
iihVV Nddff 00fff 1sTTT 2sTTT 3PPPP 4PPPP 5appp 6RRRt 7wwWW 8NCCC 9GGgg
222Dv 0sTTT 1PPHH 2PPHH 3dddd 4PPHH 5PPHH 6IEER 70HHH 8aTTT
333 0.... 1sTTT 2sTTT 3Ejjj 4Esss 5jjjj jjjjj 6RRRt 7RRRR 8Nchh 9SSss

000 Group - Identification and Location

• IIiii The WMO number of the station.
  Ship or Buoy Observations:
• IIIII The ship or buoy identifier
• YYGGi
YY -- The day of the month
  GG  -- The hour of the observation (UTC)
  iw -- Wind type indicator

  0 -- m/s (estimated)
  1 -- m/s (from anemometer)
  2 -- knots (estimated)
  3 -- knots (from anemometer)

• 99LLL QLLLL
LLL -- Latitude of observation to .1 degrees
  Q -- Quadrant of observation

  1 -- North east
  3 -- South east
  5 -- South west
  7 -- North west

  LLLL -- Longitude of  observation to .1 degrees

111 Group - Land Observations

• iihVV
iR -- Precipitation indicator

  0 -- Precipitation in groups 1 and 3
  1 -- Precipitation reported in group 1 only
  2 -- Precipitation reported in group 3 only
  3 -- Precipitation omitted, no precipitation
  4 -- Precipitation omitted, no observation

  ix -- Station type and present and past weather indicator

  1 -- manned station -- weather group included
  2 -- manned station -- omitted, no significant weather
  3 -- manned station -- omitted, no weather observation
  4 -- automated station -- weather group included (see automated weather codes 4677 and 4561)
  5 -- automated station -- omitted, no significant weather
  6 -- automated station -- omitted, no weather observation
  7 -- automated station -- weather group included (see automated weather codes 4680 and 4531)

  h -- Cloud base of lowest cloud seen (meters above ground)

  0 -- 0 to 50 m
  1 -- 50 to 100 m
  2 -- 100 to 200 m
  3 -- 200 to 300 m
  4 -- 300 to 600 m
  5 -- 600 to 1000 m
  6 -- 1000 to 1500 m
  7 -- 1500 to 2000 m
  8 -- 2000 to 2500 m
  9 -- above 2500 m
  / -- unknown

  VV -- Visibility

  00 -- less than 0.1 km
  01 -- 0.1 km
  02 -- 0.2 km
  ...
  50 -- 5.0 km
  56 -- 6 km
  57 -- 7 km
  ...
  80 -- 30 km
  81 -- 35 km
  82 -- 40 km
  83 -- 45 km
  84 -- 50 km
  85 -- 55 km
  86 -- 60 km
  87 -- 65 km
  88 -- 70 km
  89 -- greater than 70 km
  90 -- less than 0.05 km
  91 -- 0.05 km
  92 -- 0.2 km
  93 -- 0.5 km
  94 -- 1 km
  95 -- 2 km
  96 -- 4 km
  97 -- 10 km
  98 -- 20 km
  99 -- greater than 50 km
  // -- missing

• Nddff
N -- Total cloud cover

  0 -- 0 eighths (clear)
  1 -- 1/8th
  2 -- 2/8ths
  3 -- 3/8ths
  4 -- 4/8ths
  5 -- 5/8ths
  6 -- 6/8ths
  7 -- 7/8ths
  8 -- 8/8ths (overcast)
  9 -- sky obscured
  / -- no observation

  dd -- wind direction in 10s of degrees
  ff -- wind speed in units determined by wind type indicator (see above)

• 00fff (optional)
  fff -- wind speed if value greater than 100
• 1sTTT -- Temperature
  s -- sign of temperature (0=positive, 1=negative)
  TTT -- Temperature in .1 C
• 2sTTT -- Dewpoint
  s -- sign of temperature (0=positive, 1=negative, 9 = RH)
  TTT -- Dewpoint temperature in .1 C (if sign is 9, TTT is relative humidity)
• 3PPPP -- Station pressure in 0.1 mb (thousandths digit omitted, last digit can be slash, then pressure in full mb)
• 4PPPP -- Sea level pressure in 0.1 mb (thousandths digit omitted, last digit can be slash, then pressure in full mb)
  4ahhh -- Geopotential of nearest mandatory pressure level (use for high altitude stations where sea level pressure reduction is not accurate)
  a3 -- mandatory pressure level

  1 -- 1000 mb
  2 -- 925 mb
  5 -- 500 mb
  7 -- 700 mb
  8 -- 850 mb

  hhh -- geopotential height omitting thousandths digit

• 5appp -- Pressure tendency over 3 hours
  a -- characteristics of pressure tendency

  0 -- Increasing, then decreasing -- resultant pressure same or higher
  1 -- Increasing, then steady -- resultant pressure higher
  2 -- Increasing steadily -- resultant pressure higher
  3 -- Decreasing or steady, then increasing -- resultant pressure higher
  4 -- Steady -- resultant pressure same
  5 -- Decreasing, then increasing -- resultant pressure lower
  6 -- Decreasing, then steady -- resultant pressure lower
  7 -- Decreasing steadily -- resultant pressure lower
  8 -- Increasing or steady, then decreasing -- resultant pressure lower

  ppp -- 3 hour pressure change in 0.1 mb

• 6RRRt -- Liquid precipitation
  RRR -- Precipitation amount in mm

  001 -- 1 mm
  002 -- 2 mm
  ...
  988 -- 988 mm
  989 -- 989 or more mm
  990 -- Trace
  991 -- 0.1 mm
  992 -- 0.2 mm
  ...
  999 -- 0.9 mm

  t -- Duration over which precipitation amount measured

  1 -- 6 hours
  2 -- 12 hours
  3 -- 18 hours
  4 -- 24 hours
  5 -- 1 hour
  6 -- 2 hours
  7 -- 3 hours
  8 -- 9 hours
  9 -- 15 hours
  / -- 24 hours

• 7wwWW -- Present and past weather
  ww -- Present weather

  00 -- clear skies
  01 -- clouds dissolving
  02 -- state of sky unchanged
  03 -- clouds developing
  Haze, smoke, dust or sand
  04 -- visibility reduced by smoke
  05 -- haze
  06 -- widespread dust in suspension not raised by wind
  07 -- dust or sand raised by wind
  08 -- well developed dust or sand whirls
  09 -- dust or sand storm within sight but not at station
  Non-precipitation events
  10 -- mist
  11 -- patches of shallow fog
  12 -- continuous shallow fog
  13 -- lightning visible, no thunder heard
  14 -- precipitation within sight but not hitting ground
  15 -- distant precipitation but not falling at station
  16 -- nearby precipitation but not falling at station
  17 -- thunderstorm but no precipitation falling at station
  18 -- squalls within sight but no precipitation falling at station
  19 -- funnel clouds within sight
  Precipitation within past hour but not at observation time
  20 -- drizzle
  21 -- rain
  22 -- snow
  23 -- rain and snow
  24 -- freezing rain
  25 -- rain showers
  26 -- snow showers
  27 -- hail showers
  28 -- fog
  29 -- thunderstorms
  Duststorm, sandstorm, drifting or blowing snow
  30 -- slight to moderate duststorm, decreasing in intensity
  31 -- slight to moderate duststorm, no change
  32 -- slight to moderate duststorm, increasing in intensity
  33 -- severe duststorm, decreasing in intensity
  34 -- severe duststorm, no change
  35 -- severe duststorm, increasing in intensity
  36 -- slight to moderate drifting snow, below eye level
  37 -- heavy drifting snow, below eye level
  38 -- slight to moderate drifting snow, above eye level
  39 -- heavy drifting snow, above eye level
  Fog or ice fog
  40 -- Fog at a distance
  41 -- patches of fog
  42 -- fog, sky visible, thinning
  43 -- fog, sky not visible, thinning
  44 -- fog, sky visible, no change
  45 -- fog, sky not visible, no change
  46 -- fog, sky visible, becoming thicker
  47 -- fog, sky not visible, becoming thicker
  48 -- fog, depositing rime, sky visible
  49 -- fog, depositing rime, sky not visible
  Drizzle
  50 -- intermittent light drizzle
  51 -- continuous light drizzle
  52 -- intermittent moderate drizzle
  53 -- continuous moderate drizzle
  54 -- intermittent heavy drizzle
  55 -- continuous heavy drizzle
  56 -- light freezing drizzle
  57 -- moderate to heavy freezing drizzle
  58 -- light drizzle and rain
  59 -- moderate to heavy drizzle and rain
  Rain
  60 -- intermittent light rain
  61 -- continuous light rain
  62 -- intermittent moderate rain
  63 -- continuous moderate rain
  64 -- intermittent heavy rain
  65 -- continuous heavy rain
  66 -- light freezing rain
  67 -- moderate to heavy freezing rain
  68 -- light rain and snow
  69 -- moderate to heavy rain and snow
  Snow
  70 -- intermittent light snow
  71 -- continuous light snow
  72 -- intermittent moderate snow
  73 -- continuous moderate snow
  74 -- intermittent heavy snow
  75 -- continuous heavy snow
  76 -- diamond dust
  77 -- snow grains
  78 -- snow crystals
  79 -- ice pellets
  Showers
  80 -- light rain showers
  81 -- moderate to heavy rain showers
  82 -- violent rain showers
  83 -- light rain and snow showers
  84 -- moderate to heavy rain and snow showers
  85 -- light snow showers
  86 -- moderate to heavy snow showers
  87 -- light snow/ice pellet showers
  88 -- moderate to heavy snow/ice pellet showers
  89 -- light hail showers
  90 -- moderate to heavy hail showers
  Thunderstorms
  91 -- thunderstorm in past hour, currently only light rain
  92 -- thunderstorm in past hour, currently only moderate to heavy rain
  93 -- thunderstorm in past hour, currently only light snow or rain/snow mix
  94 -- thunderstorm in past hour, currently only moderate to heavy snow or rain/snow mix
  95 -- light to moderate thunderstorm
  96 -- light to moderate thunderstorm with hail
  97 -- heavy thunderstorm
  98 -- heavy thunderstorm with duststorm
  99 -- heavy thunderstorm with hail

  W1 -- Past weather (type 1)
  W2 -- Past weather (type 2)

  0 -- cloud covering less than half of sky
  1 -- cloud covering more than half of sky during part of period and more than half during part of period
  2 -- cloud covering more thna half of sky
  3 -- sandstorm, duststorm or blowing snow
  4 -- fog, or thick haze
  5 -- drizzle
  6 -- rain
  7 -- snow or mixed rain and snow
  8 -- showers
  9 -- thunderstorms

• 8NCCC -- Cloud type information
  N -- Amount of low clouds covering sky, if no low clouds, the amount of the middle clouds
  CL -- Low cloud type

  0 -- no low clouds
  1 -- cumulus humulis or fractus (no vertical development)
  2 -- cumulus mediocris or congestus (moderate vertical development)
  3 -- cumulonimbus calvus (no outlines nor anvil)
  4 -- stratocumulus cumulogenitus (formed by spreading of cumulus)
  5 -- stratocumulus
  6 -- stratus nebulosus (continuous sheet)
  7 -- stratus or cumulus fractus (bad weather)
  8 -- cumulus and stratocumulus (multilevel)
  9 -- cumulonimbus with anvil
  / -- low clouds unobserved due to darkness or obscuration

  CM -- Middle cloud type

  0 -- no middle clouds
  1 -- altostratus translucidous (mostly transparent)
  2 -- altostratus opacus or nimbostratus
  3 -- altocumulus translucidous (mostly transparent)
  4 -- patches of altocumulus (irregular, lenticular)
  5 -- bands of altocumulus
  6 -- altocumulus cumulogenitus (formed by spreading of cumulus)
  7 -- altocumulus (multilayers)
  8 -- altocumulus castellanus (having cumuliform tufts)
  9 -- altocumulus of a chaotic sky
  / -- middle clouds unobserved due to darkness or obscuration

  CH -- High cloud type

  0 -- no high clouds
  1 -- cirrus fibratus (wispy)
  2 -- cirrus spissatus (dense in patches)
  3 -- cirrus spissatus cumulogenitus (formed out of anvil)
  4 -- cirrus unicus or fibratus (progressively invading sky)
  5 -- bands of cirrus or cirrostratus invading sky (less than 45 degree above horizon)
  6 -- bands of cirrus or cirrostratus invading sky (more than 45 degree above horizon)
  7 -- cirrostratus covering whole sky
  8 -- cirrostratus not covering sky but not invading
  9 -- cirrocumulus
  / -- high clouds unobserved due to darkness or obscuration

• 9GGgg -- Time of observation in hours and minutes

222 Group - Sea Surface Observations

• 222Dv
D -- direction of ship movement

  0 -- calm
  1 -- NE
  2 -- E
  3 -- SE
  4 -- S
  5 -- SW
  6 -- W
  7 -- NW
  8 -- N
  9 -- unknown

• v -- ship's average speed

  0 -- 0 knots
  1 -- 1 to 5 knots
  2 -- 6 to 10 knots
  3 -- 11 to 15 knots
  4 -- 16 to 20 knots
  5 -- 21 to 25 knots
  6 -- 26 to 30 knots
  7 -- 31 to 35 knots
  8 -- 36 to 40 knots
  9 -- over 40 knots

• 0sTTT -- Sea surface temperature
  s -- sign of temperature (0=positive, 1=negative)
  TTT -- Temperature in .1 C
• 1PPHH -- Wave heights in 0.5 m increments
  PP -- Period of waves in seconds
  HH -- Height of waves in 0.5 m increments
• 2PPHH -- Wave period and heights (instrumented)
• 3dddd -- Direction of swells (up to 2 swells)
• 4PPHH -- Period and direction of first set of swells
• 5PPHH -- Period and direction of second set of swells
• 6IEER -- Ice accretion on ships
• 70HHH -- Wave heights to 0.1 m (instrumented)
• 8aTTT -- Wet bulb temperature

333 Group - Special / Climatological Data

• 0.... -- Regionally developed data
• 1sTTT -- Maximum temperature over previous 24 hours
  s -- sign of temperature (0=positive, 1=negative)
  TTT -- Temperature in .1 C
• 2sTTT -- Minimum temperature over previous 24 hours
  s -- sign of temperature (0=positive, 1=negative)
  TTT -- Temperature in .1 C
• 3Ejjj -- Regionally developed data
• 4Esss -- Snow depth
  E -- State of ground with snow cover

  0 -- predominantly covered with ice
  1 -- compact or wet snow covering less than half of ground
  2 -- compact or wet snow covering more than half of ground but not completely covered
  3 -- even layer of compact or wet snow covering entire ground
  4 -- uneven layer of compact or wet snow covering entire ground
  5 -- loose dry snow covering less than half of ground
  6 -- loose dry snow covering more than half of ground but not completely covered
  7 -- even layer of loose dry snow covering entire ground
  8 -- uneven layer of loose dry snow covering entire ground
  9 -- snow covering ground completely with deep drifts

  sss -- snow depth in cm

• 5jjjj jjjjj -- Additional information (can be multiple groups)
• 6RRRt -- Liquid precipitation
  RRR -- Precipitation amount in mm

  001 -- 1 mm
  002 -- 2 mm
  ...
  988 -- 988 mm
  989 -- 989 or more mm
  990 -- Trace
  991 -- 0.1 mm
  992 -- 0.2 mm
  ...
  999 -- 0.9 mm

• t -- Duration over which precipitation amount measured

  1 -- 6 hours
  2 -- 12 hours
  3 -- 18 hours
  4 -- 24 hours
  5 -- 1 hour
  6 -- 2 hours
  7 -- 3 hours
  8 -- 9 hours
  9 -- 15 hours
  / -- 24 hours

• 7RRRR -- 24 hour precipitation in mm
• 8NChh -- Cloud layer data
  N -- cloud coverage of layer
  C -- genus of cloud

  0 -- cirrus (Ci)
  1 -- cirrocumulus (Cc)
  2 -- cirrostratus (Cs)
  3 -- altocumulus (Ac)
  4 -- altostratus (As)
  5 -- nimbostratus (Ns)
  6 -- stratocumulus (Sc)
  7 -- stratus (St)
  8 -- cumulus (Cu)
  9 -- cumulonimbus (Cb)
  / -- cloud not visible

• hh -- height of cloud base

  00 -- less than 30 m
  01 -- 30 m (100 ft)
  02 -- 60 m (200 ft)
  03 -- 90 m (300 ft)
  ...
  50 -- 1500 m (5000 ft)
  56 -- 1800 m (6000 ft)
  57 -- 2100 m (7000 ft)
  ...
  80 -- 9000 m (30000 ft)
  81 -- 10500 m
  82 -- 12000 m
  ...
  88 -- 21000 m
  89 -- greater than 21000 m
  90 -- 0 to 50 m
  91 -- 50 to 100 m
  92 -- 100 to 200 m
  93 -- 200 to 300 m
  94 -- 300 to 600 m
  95 -- 600 to 1000 m
  96 -- 1000 to 1500 m
  97 -- 1500 to 2000 m
  98 -- 2000 to 2500 m
  99 -- above 2500 m

• 9SSss -- Supplementary information