Periodic Additional Data and World Meteorological Organization Codes

Steve Sconfienza, Ph.D.

Airline Transport Pilot

Flight Instructor: Airplane Single and Multiengine; Instrument Airplane

cell: 518.366.3957


This document describes how to decode the periodic additional data on METARs and gives details of the Meteorological codes for use at observing stations.

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Periodic Additional Data

Selected common additional data blocks

Note: for temperature reports, Sn indicates the Sign of the temperature: 0 for positive or zero degrees and 1 for negative degrees

Data Blocks
Data   Descriptor
Hourly Temperature and Dew point TSnTTTSnTdTdTd
(in 0.1 degrees C)
6-Hour Maximum Temperature
(in six-hour report*)
(in 0.1 degrees C)
6-Hour Minimum Temperature
(in six-hour report*)
(in 0.1 degrees C
24-Hour Maximum/Minimum Temperature
(in 0000 local standard time report)
(in 0.1 degrees C)
3-Hour Pressure Tendency
(in three- and six-hour reports*)
(in hectopascals, starting at 10s)
(see tendency code in table 12-7 below)
3- and 6-Hour Precipitation Amount
(in three- and six-hour reports, respectively*)
(in inches, starting at 10s)
(see also precipitation units in table 12-6 below)
24-Hour Precipitation Amount
(in 1200 UTC report)
(in inches, starting at 10s)
(see also precipitation units in table 12-6 below)
Hourly Precipitation Amount
(if precipitation has occurred since last METAR)
(in inches, starting at 10s)
(see also precipitation units in table 12-6 below)
Snow Depth on the Ground
(in six-hour reports*)
(in inches, starting at 100s)
Cloud Types
(in three- and six-hour reports*)
(Cloud types as per WMO International Cloud Atlas)
Water Equivalent of Snow on Ground
(in 1800 UTC report if snow greater than 2 inches)
(in inches, starting at 10s)
Duration of Sunshine
(in 0800 UTC report)
(in minutes)

* Three-hour report: 0300, 0900, 1500, 2100 UTC
* Six-hour report: 0000, 0600, 1200, 1800 UTC
Equipment and Sensor Status Codes
RVRNO: Runway Visual Range missing
PWINO: Precipitation Identifier Information not available
PNO: Precipitation Amount not available
FZRANO: Freezing Rain information not available
TSNO: thunderstorm information not available (may indicate augmenting weather observer not logged on)
VISNO_LOC: (Visibility) at second location not available
CHINO_LOC: (Cloud Height Indicator) sky condition at secondary location not available
$ Maintenance Check Indicator:

Additional data blocks may be decoded as follows:
DataData BlockDescription
CLOUD HEIGHT/VISIBILITY iRiXhVV The  iR  is  the  precipitation  data  (group  6RRRtR) indicator (WMO code table 1819 -- see reference for WMO code tables below), 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 SnTTT The Snis 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 SnTdTdTd The TdTdTd is the dew-point temperature in tens, units, and tenths of a degree Celsius.
NOTE: In the body of a METAR (as opposed to the additional data blocks)
  • The air temperature/dew point temperature group is coded TT/TdTd rounded to whole numbers;
  • For minus readings an M is prefixed, thus TT/MTdTd or MTT/MTdTd
STATION PRESSURE 3POPOPOPO The POPOPOPO is the station pressure in hundreds, tens, units, and tenths of hPa (thousands value omitted). [see note "P" below.]
SEA-LEVEL PRESSURE 4PPPP Also indicated by SLP instead of a 4, the PPPP is the sea-level pressure in hundreds, tens, units, and tenths of hPa (thousands value omitted) [see note "P" below.].
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. [see note "P" below.] [See FMH No. 1, Table 12-7 following.]

FMH Table 12-6:
Units of Measure for Precipitation.

Precipitation measurements shall be in inches, tenths of inches, or hundredths of inches depending on the precipitation being measured.
Taken from the Federal Metorological Handbook No. 1
Type of Measurement Unit of Measure
Liquid Precipitation 0.01 inch
Water Equivalent of Solid Precipitation 0.01 inch
Solid Precipitation 0.1 inch
Snow Depth 1.0 inch
FMH Table 12-7:
Characteristics of Barometer Tendency

Taken from the Federal Metorological Handbook No. 1
Description Code
pressure now
higher than 3
hours ago.
Increasing, then decreasing. 0
Increasing, then steady, or increasing then
increasing more slowly.
Increasing steadily or unsteadily. 2
Decreasing or steady, then increasing; or
increasing then increasing more rapidly.
pressure now
same as 3 hours
Increasing, then decreasing. 0
Steady 4
Decreasing then increasing. 5
pressure now
lower than 3
hours ago.
Decreasing, then increasing. 5
Decreasing, then steady, or decreasing then
decreasing more slowly.
Decreasing steadily or unsteadily. 7
Steady or increasing, then decreasing; or
decreasing then decreasing more rapidly.
  • 0, 1, 2, & 3: pressure is higher (or same if 0 & pressure change = 000)
  • 5, 6, 7, & 8: pressure is lower (or same if 5 & pressure change = 000)
  • 4: pressure is same (and 0 & 5 if pressure change = 000)

Notes and References


Note P: The terms "hectopascal" and "millibar" are synonomous. While the term millibar predates the term hectopascal in general aviation use, the Pascal is the SI (metric system) unit for pressure and is thus the now-accepted term for the measure of atmospheric pressure.

The standard conversions are


The Federal Meteorological, Handbook No. 1, Office of the Federal Coordinator for Meteorology, retrieved 13 March 2014.

World Meteorological Organization (WMO)