Table 3-5.—Symbolic Format of Land Station Synoptic Weather Observation Report (WMO Code FM 12 XI SYNOP)
AAXX YYGGiw IIiii iRiXh Nddff (00fff) lsnTTT 2SnTdTdTd 3POPOPOPO 4PPPP (or
4a3hhh) 5appp 6RRRtR 7wwW1W2 8NhCLCMCH 9GGgg 333 0. . . . lSnTXTXTX 2SnTnTnTn
3Ejjj 4E'sss 5j1j2j3j4 (j5j6j7j8j9) 6RRRtR 7R24R24R24R24 8NsChshs 9SPSPSpSP 444 N'C'H'H'Ct
555;
Identification Data
The first few groups of the Synoptic code represent
Section 0, the Identification Data section. The
Identification Data section contains a data identifier, a
date-time group, and a station identifier.
DATA IDENTIFIER.—The data identifier for a
land synoptic report is the first group, which is always
AAXX.
DATE-TIME GROUP.—YYGGiW. This group
provides the day of the month and the hour of the report,
as well as an indicator for the wind speed. YY is the UTC
day of the month (two digits), GG is the UTC hour of
report (00, 03, 06, etc.), and iW is the indicator for source
and units of wind speed (WMO code table 1855).
STATION IDENTIFIER.—IIiii. The station
identifier is composed of the WMO block number and
the three-digit station number. II is the WMO block
number, and iii is the WMO station number. Each
WMO region is subdivided into data block areas. Large
countries may be designated as a data block, or several
smaller, adjoining countries may be grouped together to
form a block. In North America the United States is
block 72, with supplemental stations belonging to block
74. Alaska is block 70. Canada is block 71; Mexico is
block 76; and all the countries of the Caribbean and
Central America are grouped as block 78.
International Data
Section 1 of the Synoptic code contains
meteorological data for international exchange, and
immediately follows the identification data. This
section consists of cloud height and visibility, winds,
sky coverage, air temperature, dew-point temperature,
station pressure and sea-level pressure, pressure
change, precipitation, and weather groups. In North
America (WMO Region IV), it also contains a group for
cloud type. Most of the five-digit groups begin with a
group identifier number that does not change.
CLOUD HEIGHT/VISIBILITY.—iRiXhVV.
The iR is the precipitation data (group 6RRRtR)
indicator (WMO code table 1819), while iX is the
indicator for station type (manned or unmanned) and for
present and past weather (group 7wwW1W2) (WMO
code table 1860). The h is height (AGL) of lowest cloud
(WMO code table 1600), and VV is horizontal surface
visibility (WMO code table 4377).
SKY COVERAGE/WIND.—Nddff. The N is
total sky cover in eighths or oktas (WMO code table
2700), while dd is the wind direction (hundreds and tens
of degrees true) to the nearest 10 degrees, and ff is the
sustained wind speed in the units indicated by iW. If
winds exceed 99 (knots or meters per second), ff is
encoded 99 and the 00fff group is included, with 00 as an
indicator and fff as the wind speed in hundreds, tens, and
units.
AIR TEMPERATURE.—1SnTTT. The Sn is the
temperature sign, 0 for positive (or 0) and 1 for negative.
This indicator is used throughout the Synoptic code to
indicate the temperature sign. The TTT is the
temperature in tens, units, and tenths of a degree
Celsius.
DEW-POINT TEMPERATURE.—2SnTdTdTd
The TdTdTd is the dew-point temperature in tens, units,
and tenths of a degree Celsius.
STATION PRESSURE.—3POPOPOPO. The
POPOPOPO is the station pressure in hundreds, tens,
units, and tenths of hPa (thousands value omitted).
SEA-LEVEL PRESSURE—4PPPP. The PPPP
is the sea-level pressure in hundreds, tens, units, and
tenths of hPa (thousands value omitted).
STANDARD LEVEL HEIGHT.—4a3hhh.
Reported by mountain stations in place of sea-level
pressure, a3 is the standard isobaric surface reported
(WMO code table 0264) and hhh is the geopotential
height in meters, omitting thousands value.
3-HOUR PRESSURE CHANGE.—5appp. The
a is the pressure tendency (WMO code table 0200), and
ppp is the 3-hour pressure change in tens, units, and
tenths of hPa.
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