Decoding Synops

Explains how to decode a synoptic observation, used by weather stations around the world.

A synop is a report of a surface observation from a land based station. A typical synop will have the following format:

and can be decoded as follows: 
AAAAA- Station's five digit identification number
B- Indicator for inclusion or omission of precipitation data:
         1          In section 1 (regional codes indicated by ###=111)
         2          In section 3 (regional codes indicated by ###=333)
         3          Precipitation amount=0
         4          Precipitation amount not available
C- Indicator for type of station operation:
         1,2,3      Manned
         4,5,6      Automatic
D- Height above surface of the base of the lowest cloud seen:
         0          0-50 meters
         1          50-100 meters
         2          100-200 meters
         3          200-300 meters
         4          300-600 meters
         5          600-1000 meters
         6          1000-1500 meters
         7          1500-2000 meters
         8          2000-2500 meters
         9          2500 or more, or no clouds at all
         /          Height at base of cloud not known or the base of
                    the clouds is at a lower level and the tops are
                    at a higher level than that of the station.
EE- Horizontal visibility at the surface:
      For EE=00 to EE=50: visibility in tenths of kilometers
                         (ex: 31=3.1km)
      For EE=56 to EE=80: visibility in kilometers + 50 (ex: 67=17km)
         81        35km     86        60km
         82        40km     87        65km
         83        45km     88        70km
         84        50km     89        >70km
F- Total cloud cover in oktas (eights):
         0         No cloud cover
         1-8       Cloud cover in eights
         9         Sky obscured by fog and/or other meteorological
         /         Cloud cover is indiscernable for reasons other
                   than fog or other meteorological phenomena, or the
                   observation was not made.
GG- True direction, in tens of degrees, from which the wind is blowing:
      Ex:   27=270 degrees (west wind)
HH- Wind speed in meters per second:
      Ex:   13=13 meters per second (~ 26 mph)
      1,2,3,4,5- Group number
I- Sign of the following data:
         0         Postive or zero
         1         Negative
JJJ- Temperature in tenths of degrees Celsius. Used in combination with 
      Ex:   0123= 12.3 degrees above zero
            1034= 3.4 degress below zero
K- Same as "I"
LLL- Dew point temperature in tenths of degrees Celsius. Used the same 
     as "JJJ".
MMMM- Station pressure, not reduced to sea level:
NNNN- Station pressure reduced to sea level:
      NNNN greater than 5000  Station pressure in tenths of millibars
      NNNN less than 5000  Add a preceding 1 to get the corrected surface 
           pressure in tenths of millibars.
      Ex:   9872 = 987.2 millibars
            0305 = 1030.5 millibars
O- Pressure tendency during the three previous hours preceding the time 
    of observation:
      0     Increasing, then decreasing; atmospheric pressure the same
            or higher than 3 hours ago
      1*    Increasing, then steady; or increasing, then increasing 
            more slowly
      2*    Increasing (steadily or unsteadily)
      3*    Decreasing or steady, then increasing; or increasing, then 
            increasing more rapidly
      4     Steady; atmospheric pressure the same as three hours ago
      5     Decreasing, then increasing; atmospheric pressure the same 
            or lower than three hours ago
      6**   Decreasing, then steady; or decreasing, then decreasing 
            more slowly 
      7**   Decreasing (steadily or unsteadily)
      8**   Steady or increasing, then decreasing; or decreasing,
            then decreasing more rapidly
      *     indicates atmospheric pressure higher now than three hours
      **    indicates atmospheric pressure lower now than three hours
PPP- Pressure rise or fall in tenths of millibars
QQQ- Amount of precipitation which has fallen during the period 
     preceding the time of observation, as indicated by "R":
          000      Not used
          001      1 mm
          002      2mm (etc. up to 988)
          989      989 mm or more
          990      Trace
          991      .1 mm
          992      .2 mm (etc. up to 999 = .9mm)
R- Time period for precipitation observation (not defined in WMO
SSSS- Indicators of past or present weather phenomena (refer to WMO
      manual for decoding procedure)
T- Amount of the "U" cloud present, or if no "U" cloud is present, the
   amount of "V" cloud present:
U- Clouds of the genera Stratocumulus, Stratus, Cumulus, or
V- Clouds of the genera Cirrus, Cirrocumulus, or Cirrostratus.
W- Clouds of the genera Cirrus, Cirrocumulus, or Cirrostratus.
         For more information on the codes for "U", "V", and "W"
         refer to the WMO manual.

University of North Dakota / School of Aerospace Sciences / Atmospheric Science Department

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