SYNOP Code Form

SYNOP is the traditional WMO character-based code for the global exchange of land-based meteorological data for use on synoptic charts and in the preparation of forecasts and warnings.

The code form described below is automatically generated and displayed with the latest weather observation at the top of each hour. It closely conforms to international standards defined by WMO and supplemented by regional requirements (Asia) and national practices (Australia), with only minor changes to suit local practices.

Code Form Description WMO Regulations & Local Practices
MiMiMjMj message type identifier Always included and reported as AAXX.
YYGGiW date of the observation UTC (YY)
hour of the observation UTC (GG)
indicator for source of wind speed (iW).		 Always included.
IIiii block number (II) relates to the geographical area
station number (iii) allocated by the national meteorological agency		 Always included. For local practices the combination of special use block number 69 and vacant station number 259 were chosen.
iRiXhVV indicator for inclusion of rainfall data (iR)
indicator for station operation (iX)
height of the base of lowest cloud (h) either low or middle level cloud
horizontal visibility (VV)		 Always included.
Nddff total amount of cloud (N)
mean wind direction (dd) in the 10 minutes prior to the time of the observation
mean wind speed (ff) in the 10 minutes prior to the time of the observation		 Always included.
1snTTT group identifier (1)
indicator for sign of the temperature (sn)
dry bulb temperature (TTT)		 Only included if data are available
2snTdTdTd group identifier (2)
indicator for sign of the temperature (sn)
dew point temperature (TdTdTd)		 Only included if data are available
4PPPP group identifier (4)
mean sea level pressure (PPPP)		 Only included if datum is available
5appp group identifier (5)
indicator for pressure trend (a)
pressure tendency (ppp) in the 3 hours prior to the time of the observation		 Only included if data are available. For local practices these data shall be for the one hour prior to the time of the observation.
6RRRtR group identifier (6)
amount of rainfall (RRR)
indicator for period of rainfall (tR)		 Reported as /// if the amount is unavailable, or omitted if the amount is zero. Always included at the WMO standard times (every six hours) or intermediate times (every three hours) if data are available. For local practices these data are reported every three hours.
7wwW1W2 group identifier (7)
type of present weather (WW) at or just prior to the time of the observation
type of past weather (W1 and W2) typically in the past 3 hours		 Only included if data are available.
8NhCLCMCH group identifier (8)
amount of lowest cloud (Nh) either low or middle level cloud
type of low level cloud (CL)
type of middle level cloud (CM)
type of high level cloud (CH)		 Only included if data are available.
333 regional section identifier Only included if one or more regional groups are reported.
5EEEie group identifier (5)
amount of evaporation (EEE) recorded in the 24 hours to 09:00 local time
indicator for evaporation instrumentation (ie)		 Regional group. Included at 00:00 UTC if data are available.
55SSS group identifier (55)
duration of sunshine (SSS) recorded yesterday		 Regional group. Included at 00:00 UTC if datum is available.
6RRRtR group identifier (6)
amount of rainfall (RRR)
indicator for period of rainfall (tR)		 Regional group. Reported as /// if the amount is unavailable, or omitted if the amount is zero. Always included if data are available. For local practices these data are reported every hour.
7R24R24R24R24 group identifier (7)
amount of rainfall (R24R24R24R24) recorded in the 24 hours to 00:00 UTC		 Regional group. Reported as /// if the amount is unavailable. Always included at 00:00 UTC.
555 national section identifier Only included if one or more national groups are reported.
1snTxTxTx group identifier (1)
indicator for sign of the temperature (sn)
maximum temperature (TxTxTx)		 National group specified by Australia. Included for local practices at 18:00, 19:00 and 20:00 local time if data are available, for data recorded between 09:00 to 18:00 local time.
2snTnTnTn group identifier (2)
indicator for sign of the temperature (sn)
minimum temperature (TnTnTn)		 National group specified by Australia. Included for local practices at 09:00, 10:00 and 11:00 local time if data are available, for data recorded in the 24 hours to 09:00 local time.
910fgfg group identifier (910)
highest wind gust (fgfg) in the 10 minutes prior to the time of the observation		 National group specified by the USA. Only included for local practices if datum is available.

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