Steve's Musings on Life: Steve's Flying Pages: Periodic Additional Data and World Meteorological Oranization Codes

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

e-mail: docsteve@localnet.com

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

Note: for temperature reports, S_n 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	TS_nTTTS_nT_dT_dT_d (in 0.1 degrees C)
6-Hour Maximum Temperature (in six-hour report*)	1S_nT_xT_xT_x (in 0.1 degrees C)
6-Hour Minimum Temperature (in six-hour report*)	2S_nT_nT_nT_n (in 0.1 degrees C
24-Hour Maximum/Minimum Temperature (in 0000 local standard time report)	4S_nT_xT_xT_xS_nT_nT_nT_n (in 0.1 degrees C)
3-Hour Pressure Tendency (in three- and six-hour reports*)	5appp (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*)	6RRRR (in inches, starting at 10s) (see also precipitation units in table 12-6 below)
24-Hour Precipitation Amount (in 1200 UTC report)	7R₂₄R₂₄R₂₄R₂₄ (in inches, starting at 10s) (see also precipitation units in table 12-6 below)
Hourly Precipitation Amount (if precipitation has occurred since last METAR)		Prrrr (in inches, starting at 10s) (see also precipitation units in table 12-6 below)
Snow Depth on the Ground (in six-hour reports*)	4/sss (in inches, starting at 100s)
Cloud Types (in three- and six-hour reports*)	8/C_LC_MC_H (Low/Middle/High) (Cloud types as per WMO International Cloud Atlas)
Water Equivalent of Snow on Ground (in 1800 UTC report if snow greater than 2 inches)	933RRR (in inches, starting at 10s)
Duration of Sunshine (in 0800 UTC report)	98mmm (in minutes)
* Three-hour report: 0300, 0900, 1500, 2100 UTC * Six-hour report: 0000, 0600, 1200, 1800 UTC

Data Blocks

Data

Descriptor

Hourly Temperature and Dew point

TS_nTTTS_nT_dT_dT_d
(in 0.1 degrees C)

6-Hour Maximum Temperature
(in six-hour report*)

1S_nT_xT_xT_x
(in 0.1 degrees C)

6-Hour Minimum Temperature
(in six-hour report*)

2S_nT_nT_nT_n
(in 0.1 degrees C

24-Hour Maximum/Minimum Temperature
(in 0000 local standard time report)

4S_nT_xT_xT_xS_nT_nT_nT_n
(in 0.1 degrees C)

3-Hour Pressure Tendency
(in three- and six-hour reports*)

5appp
(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*)

6RRRR
(in inches, starting at 10s)
(see also precipitation units in table 12-6 below)

24-Hour Precipitation Amount
(in 1200 UTC report)

7R₂₄R₂₄R₂₄R₂₄
(in inches, starting at 10s)
(see also precipitation units in table 12-6 below)

Hourly Precipitation Amount
(if precipitation has occurred since last METAR)

Prrrr
(in inches, starting at 10s)
(see also precipitation units in table 12-6 below)

Snow Depth on the Ground
(in six-hour reports*)

4/sss
(in inches, starting at 100s)

Cloud Types
(in three- and six-hour reports*)

8/C_LC_MC_H
(Low/Middle/High)
(Cloud types as per WMO International Cloud Atlas)

Water Equivalent of Snow on Ground
(in 1800 UTC report if snow greater than 2 inches)

933RRR
(in inches, starting at 10s)

Duration of Sunshine
(in 0800 UTC report)

98mmm
(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:

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:**
Data	Data Block	Description
CLOUD HEIGHT/VISIBILITY	i_Ri_XhVV	The i_R is the precipitation data (group 6RRRt_R) indicator (WMO code table 1819 -- see reference for WMO code tables below), while i_X 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 i_W. 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	S_nTTT	The S_nis 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	S_nT_dT_dT_d	The T_dT_dT_d 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/T_dT_d rounded to whole numbers; For minus readings an M is prefixed, thus TT/MT_dT_d or MTT/MT_dT_d

STATION PRESSURE	3P_OP_OP_OP_O	The P_OP_OP_OP_O 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.]

Additional data blocks may be decoded as follows:

Data

Data Block

Description

CLOUD HEIGHT/VISIBILITY

i_Ri_XhVV

The i_R is the precipitation data (group 6RRRt_R) indicator (WMO code table 1819 -- see reference for WMO code tables below), while i_X 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 i_W. 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

S_nTTT

The S_nis 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

S_nT_dT_dT_d

The T_dT_dT_d 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/T_dT_d rounded to whole numbers;
For minus readings an M is prefixed, thus TT/MT_dT_d or MTT/MT_dT_d

STATION PRESSURE

3P_OP_OP_OP_O

The P_OP_OP_OP_O 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 12-6:
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
Primary Requirement	Description	Code Figure
Atmospheric pressure now higher than 3 hours ago.	Increasing, then decreasing.	0
Increasing, then steady, or increasing then increasing more slowly.	1
Increasing steadily or unsteadily.	2
Decreasing or steady, then increasing; or increasing then increasing more rapidly.	3
Atmospheric pressure now same as 3 hours ago.	Increasing, then decreasing.	0
Steady	4
Decreasing then increasing.	5
Atmospheric pressure now lower than 3 hours ago.	Decreasing, then increasing.	5
Decreasing, then steady, or decreasing then decreasing more slowly.	6
Decreasing steadily or unsteadily.	7
Steady or increasing, then decreasing; or decreasing then decreasing more rapidly.	8
NOTE: 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)

FMH Table 12-7:
Characteristics of Barometer Tendency
Taken from the Federal Metorological Handbook No. 1

Primary
Requirement

Description

Code
Figure

Atmospheric
pressure now
higher than 3
hours ago.

Increasing, then decreasing.

Increasing, then steady, or increasing then
increasing more slowly.

Increasing steadily or unsteadily.

Decreasing or steady, then increasing; or
increasing then increasing more rapidly.

Atmospheric
pressure now
same as 3 hours
ago.

Increasing, then decreasing.

Steady

Decreasing then increasing.

Atmospheric
pressure now
lower than 3
hours ago.

Decreasing, then increasing.

Decreasing, then steady, or decreasing then
decreasing more slowly.

Decreasing steadily or unsteadily.

Steady or increasing, then decreasing; or
decreasing then decreasing more rapidly.

NOTE:

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

Notes:

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

100 Pascals = 1 hPa
1 hPa = 1 mb
1000 hPas = 1 bar
1 ICAO Standard Atmosphere (standard day: 15°C/59°F)
- = 1013.25 hectopascals (i.e., 1013.25 millibars)
- = 29.92 inches of mercury
1000 hPas (i.e., 1 bar) = approximately 380 feet MSL, standard day.

References:

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

World Meteorological Organization (WMO)

Manual on Codes - International Codes, Volume I.1: part A- Alphanumeric Codes; Section C, "Specification of Code Figures (Code Tables)"; b, "Code Tables"; retrieved 13 March 2014.
International Cloud Atlas, Volume I: Manual on the Observation of Clouds and Other Meteors (contains a descriptive and explanatory text concerning the general classification of meteors (Part I), clouds (Part II) and meteors other than clouds (Part III); retrieved 13 March 2014.
International Cloud Atlas, Volume II (contains 196 pages of photographs) retrieved 13 March 2014.