CODE CONVERSION

CHAPTER 3:
CODE CONVERSION - AWOS

3.1 METAR/TAF Implementation
3.2 Binary Universal Form - Representation of Codes(BUFR)

3.2.1 BUFR Overview

3.3.1 Symbolic METAR and SPECI Code
3.3.2 Example of a METAR Report from an AWOS

3.4.1 General
3.4.2 Symbolic SM Code
3.4.3 Synoptic Code - Interpretation of Symbols

3.1 METAR/TAF IMPLEMENTATION

On June 3^rd 1996 at 0600 UTC, Canada implemented the international standard METAR and TAF codes for the reporting and forecasting of aviation weather. At that time, the familiar SA and FT codes were replaced by the METAR and TAF codes, respectively, for all domestic and international weather bulletins for Canadian aerodromes. Only METAR and TAF codes for aviation sites (including AWOS sites) in Canada are being transmitted on the Global Telecommunications System (GTS ), METSIS and ANIKOM (AMIS).

There remains a number of non-aviation sites still using the SA format. Generally, these sites do not carry out a full observing program. MARS, MAPS, IWD (Inland Waters Directorate) and Campbell-Scientific (AUTO 1,2,3,4, 7 and 8) are the autostations that still report in SA format. AWOS reports exclusively in METAR. Refer to Section 2.1 for an overview of the Observational Data Flow. Refer to sections 3.2 to 3.4 for an overview of the codes (BUFR, METAR and SM) in use at AWOS sites.

3.2 BINARY UNIVERSAL FORM FOR REPRESENTATION OF CODES (BUFR)

3.2.1 BUFR OVERVIEW

The architecture of the telecommunications system is designed to allow maximum flexibility to accommodate the variety of systems being used to transmit observations. The main working principle is that the METAR code is an aviation code.

For this reason, the more comprehensive international BUFR (a binary encoded format) standard was chosen to store and transmit the complete weather observations. The entire weather observation (including tenths of degrees, precipitation accumulation, etc.) is contained in the BUFR message.

The transmitted METAR is merely a subset of this message and is intended for aviation sites only. Conversion from BUFR to METAR is performed on all necessary bulletins centrally at CMC Dorval. BUFR is converted to METAR format at CMC Dorval for transmission to the GTS , METSIS, and AMIS. To external users, the only available information from these aviation sites will be the METAR code.

BUFR code data is being distributed under the following bulletin headers:

ISAA for sites from 0 - 90 W longitude
ISAB for sites from 90 - 180 W longitude
Series 41 Manned observations
Series 51 Auto observations

3.2.1.1 BOBS (BUFR Observations Viewer)

Current TIP (Telecommunications Integration Project) release (5.01) versions available in MSC regions have a BUFR viewer (data display tool) included. More recent versions of this program are available as an add-on. The BOBS viewer allows one to examine the BUFR code information for sites in a format similar to SFC/AMSFC program. The display from BOBS can be partially configured locally to suit regional requirements.

Fig.3-1 Example of BUFR message displayed in ASCII

********************************************************
BUFR Edition 2 Table Version: Master 4, Local 4
Origin 54, Message Type: Surface data - land, subtype: 0
Header Date 96 08 20 14:00 Revision: 0
Number of Subsets 1, Observed 1 Compressed 0
********************************************************



001204 STATION IDENTIFIER, SCHEDULED OBSERVATIONS	YTL
006002 LONGITUDE (COARSE ACCURACY)	-89.00	DEGREE
004001 YEAR	1996	YEAR
004002 MONTH	8	MONTH
004003 DAY	20	DAY
004004 HOUR	14	HOUR
004005 MINUTE	0	MINUTE
001195 REPORT TYPE, SCHEDULED OBSERVATIONS	2	TABLE
002196 TYPE AUTO/SUPPLEM.(SA), SCHED. OBSERVATIONS	4	TABLE
020194 TOTAL OPACITY (SA \| STAT)	4	TENTHS
020215 TOTAL AMOUNT (SA)	MISSING
020013 HEIGHT OF BASE OF CLOUD (SA/SM)	330.0	M
020206 CLOUD COVERAGE PIREP\|SA	2	TABLE
020197 OBSCURING PHENOMENON (SA)	MISSING
008002 VERTICAL SIGNIFICANCE (SURFACE OBSERVATIONS)	MISSING
020013 HEIGHT OF BASE OF CLOUD (SA/SM)	1860.0	M
020206 CLOUD COVERAGE PIREP\|SA	2	TABLE
020197 OBSCURING PHENOMENON (SA)	MISSING
008002 VERTICAL SIGNIFICANCE (SURFACE OBSERVATIONS)	MISSING
008197 DATA QUALIFIER (SA\|METAR)	0	TABLE
008197 DATA QUALIFIER (SA\|METAR)	0	TABLE
008197 DATA QUALIFIER (SA\|METAR)	7	TABLE
020001 HORIZONTAL VISIBILITY	14480.0	M
020224 MINIMUM VISIBILITY (10 MINUTES)	15.93	METRES
020223 MAXIMUM VISIBILITY (10 MINUTES)	15.93	METRES
008197 DATA QUALIFIER (SA\|METAR)	0	TABLE
010004 PRESSURE	98800.0	PASCAL
008197 DATA QUALIFIER (SA\|METAR)	0	TABLE
010051 PRESSURE REDUCED TO MEAN SEA LEVEL	101570.0	PASCAL
008197 DATA QUALIFIER (SA\|METAR)	0	TABLE
012001 DRY BULB TEMPERATURE	285.2	K
008197 DATA QUALIFIER (SA\|METAR)	0	TABLE
012012 MINIMUM TEMPERATURE	284.3	K
012011 MAXIMUM TEMPERATURE	285.3	K
008197 DATA QUALIFIER (SA\|METAR)	0	TABLE
012003 DEW POINT TEMPERATURE	283.0	K
008021 TIME SIGNIFICANCE	2	TABLE
004025 TIME PERIOD OR DISPLACEMENT	-2	MIN
008197 DATA QUALIFIER (SA\|METAR)	0	TABLE
011011 WIND DIRECTION AT 10M	330	DEG TRUE
008197 DATA QUALIFIER (SA\|METAR)	0	TABLE
011012 WIND SPEED AT 10M	4.1	M/SEC
004025 TIME PERIOD OR DISPLACEMENT	MISSING
008197 DATA QUALIFIER (SA\|METAR)	0	TABLE
010052 ALTIMETER SETTING (QNH)	101630.0	PASCAL
008197 DATA QUALIFIER (SA\|METAR)	0	TABLE
013021 TOTAL PRECIPITATION PAST 6 HOURS	0.0	KG/M²
008197 DATA QUALIFIER (SA\|METAR)		TABLE
020210 PRESENT WEATHER (SA)	0	TABLE
008197 DATA QUALIFIER (SA\|METAR)		TABLE
013019 TOTAL PRECIPITATION PAST 1 HOUR	0.0	KG/M²
008197 DATA QUALIFIER (SA\|METAR)	0	TABLE
010063 CHARACTERISTIC OF PRESSURE TENDENCY	2	TABLE
008197 DATA QUALIFIER (SA\|METAR)	0	TABLE
010061 3-HOUR PRESSURE CHANGE	300.0	PASCAL
008021 TIME SIGNIFICANCE	2	TABLE
003013 TIME PERIOD FOR DISPLACEMENT	-1	HOUR

3.3 METAR AND SPECI

3.3.1 SYMBOLIC METAR AUTO CODE (CANADIAN DIFFERENCES INCLUDED)

METAR CCCC YYGGggZ AUTO ddffGf_mf_mKT VVVVD_v w'w' N_SN_SN_Sh_sh_sh_s or VVh_sh_sh_s or CLR TT/T'_dT'_d AP_HP_HP_HP_H RMK SLPXXX

Refer to Appendix A-5 for a complete list of the current and proposed National practices for encoding the Canadian METAR observation.

3.3.2 EXAMPLE OF A METAR REPORT FROM AN AWOS

METAR CWIK 292000Z AUTO 30015G25KT 3/4SM -SN BKN008 OVC040 M05/M08 A2992 RMK SLP134



METAR	Type of report.	Aviation Routine Weather Report. A special is indicated by SPECI.
CCCC=CWIK	Broadview, Saskatchewan	Station identifier will be 4-letter ICAO identifiers.
AUTO	AWOS Indicator	This indicates that the report is from an AWOS autostation.
YYGGggZ-292000Z	Date/Time	29th day of the month, 2000 co-ordinated universal time (UTC).
dddffGf_mf_mKT=30015G25KT	Wind	Wind is from 300 degrees True at 15 knots gusting to 25 knots.
VVVVD_v=3/4SM	Visibility	Prevailing visibility is 3/4 statute miles (SM and fractions of SM with no maximum visibility value reported. AWOS sites will report a "sensor equivalent visibility".
w'w'=-SN	Present Weather	Present weather is light snow. Present weather from an AWOS is currently only given as precipitation occurrence and intensity. AWOS can report one of the following METAR AUTO types:
		SN - Snow SHGR - Hail DZ - Drizzle RA - Rain UP - Undetermined Type FZDZ - Freezing Drizzle FZRA - Freezing Rain
		Mixed Precipitation, showers, obstructions to vision or recent weather are among the METAR present weather groups NOT reported by AWOS.
		Intensity can be one of the following for each type:
		Light (-), (e.g. -RA, Light Rain);
		Moderate ( ), (e.g. SN, Moderate Snow);
		Heavy (+), (e.g. +DZ, Heavy Drizzle).
NOTE:
Very light intensity is treated as no precipitation except when the Ice Accretion Sensor is also present and reporting weather (L) or (R). In this case very light intensity will be changed to light intensity.
N_SN_SN_Sh_sh_sh_s=BKN008 OVC040	Sky Condition	The cloud layer at 800 feet is broken, covering from 5/8 to 7/8 of the observed sky.
		The next layer at 4000 feet is overcast covering, combined with the lower layer, 8/8 of the sky, as observed from the ground.
		Layers are reported based on the summation of the layer amounts as observed from the surface up.
		The layer amounts are reported in eighths of sky coverage (oktas) as follows:
		FEW - 1 to 2, SCT - 3 to 4, BKN - 5 to 7, OVC - 8.
		Obscured sky is indicated by vertical visibility sensor (VV) and is reported in hundreds of feet.
		In AWOS reports; cloud types and amounts are not identified, cloud layers are limited to 4 layers, and clear (CLR) will be reported when no layers exist below 10000 feet.
TT/T'_dT'_d=M05/M08	Temperature/Dew Point	Temperature is -5°C, Dew point is -8°C
		Temperature and dew point are reported to the nearest whole °C. Negative values will be preceded by the letter "M".
AP_HP_HP_HP_H=A2992	Altimeter	The altimeter setting is 29.92 inches of mercury. The letter "A" prefixing the 4_digit number group indicates inches of mercury for station pressure.
PCPN 2.8MM PAST HR	Remarks	Precipitation 2.8 millimetres over the past hour.
SLP=SLP134	Mean Sea Level Pressure	The mean sea level pressure sensor is 1013.4 hPa.
		The mean sea level pressure sensor, indicated in hectopascals, will always be the last field of the METAR report, prefixed with "SLP".

3.4 SYNOPTIC CODE (SM)

(Refer to Appendix A-6 for more details on the Synoptic Code generated by AWOS.)

3.4.1 GENERAL

A synoptic message is produced for each main synoptic hour for each station. These synoptic messages are based mostly on the hourly RA reports and therefore do not comply in all respects to the requirements of a synoptic report from a manned station.

3.4.2 SYMBOLIC SM CODE

This section provides a synoptic coded message in symbolic form for observations from auto stations. Bracketed groups indicate that special conditions are required to include these groups.

3.4.2.1 Standard Format

TEXT (Symbolic Form)

IIiii i_Ri_xhVV Nddff (00fff) 1s_nTTT 2s_nT_dT_dT_d 3P_oP_oP_oP_o 4PPPP 5appp 6RRRt_R 7w_aw_aW_a1W_a2 333 1s_nT_xT_xT_x 2s_nT_nT_nT_n 7R₂₄R₂₄R₂₄R₂₄ 555 3d_md_mf_mf_m 4f_hf_tf_tf_i =

3.4.2.2 Example of Synoptic Report from an AWOS

SM 091200
71844 36264 80205 11177 21184 39934 40228 57004 333 11166 21188 70000 555 31635 40225=

3.4.3 SYNOPTIC CODE - INTERPRETATION OF SYMBOLS

This section provides a brief explanation of the meaning of the symbols in the synoptic message. For more details refer to Appendix A-6.

IIiii - international station index number - unique to each station.

i_Ri_xhVV- A 5-character group consisting of:

i_R - indicator for inclusion or omission of precipitation group; 6RRRt_R
i_x -indicator for inclusion or omission of present/past weather group; - 7w_aw_aW_a1W_a2
h - height of lowest cloud (AWOS only, otherwise '/' for missing)
VV - visibility index

Nddff - A 5-character group consisting of:

N - cloud amount (AWOS only, otherwise '/' for missing)
dd - wind direction
ff - wind speed in knots

00fff - A 5-character group consisting of:

00 - group identifier
fff - wind speed from 99 to 120 kt inclusive

1s_nTTT- A 5-character group consisting of:

1 - group identifier
s_n - sign of air temperature
TTT - air temperature in tenths of a degree Celsius

2s_nT_dT_dT_d- A 5-character group consisting of:

2 - group identifier
s_n - sign of dew point temperature
T_dT_dT_d - dew point temperature in tenths of a degree Celsius

3P_oP_oP_oP_o- A 5-character group consisting of:

3 - group identifier
P_oP_oP_oP_o - station pressure in tenths of a hectopascal

4PPPP - A 5-character group consisting of:

4 - group identifier
PPPP - Mean Sea Level Pressure in tenths of a hectopascal

5appp - A 5-character group consisting of:

5 - group identifier
a - characteristic of the pressure tendency during the preceding 3 hours
ppp - amount of pressurePressure sensor change in hectopascals and tenths during the 3 hours preceding the observation

6RRRt_R- A 5-character group consisting of:

6 - group identifier
RRR - 6-hour precipitation amount in millimetres
t_R - the code indicating time period over which RRR was measured (auto stations use code 1 only)

7w_aw_aW_a1W_a2- A 5-character group consisting of:

7 - group identifier
w_aw_a - type of present weather occurring at the time of the current main synoptic observation
W_a1W_a2 - up to 2 types of weather occurring in the 6 hours since the previous main synoptic observation

333 - section identifier

1s_nT_xT_xT_x- A 5-character group consisting of:

1 - group identifier
s_n - sign of maximum temperature
T_xT_xT_x - maximum temperature in tenths of a degree Celsius

2s_nT_nT_nT_n - A 5-character group consisting of:

2 - group identifier
s_n - sign of minimum temperature
T_nT_nT_n - minimum temperature in tenths of a degree Celsius

7R₂₄R₂₄R₂₄R₂₄- A 5-character group consisting of:

7 - group identifier
R₂₄R₂₄R₂₄R₂₄ - total amount of precipitation in tenths of a millimetre during the 24-hour period ending at the time of observation

555 - section identifier

3d_md_mf_mf_m- A 5-character group for AWOS only, consisting of:

3 - group identifier
d_md_m - wind direction associated with the maximum 24- hour wind speed during the 24 hours ending at 0600 UTC and reported in 1200 UTC message
f_mf_m - maximum 24-hour wind speed, gust or mean, during the 24 hours ending at 0600 UTC and reported in 1200 UTC message

4f_hf_tf_tf_i- A 5-character group for AWOS only, consisting of:

4 - group identifier
f_h - hundreds unit of maximum wind speed during 24 hours ending at 0600 UTC and reported in 1200 UTC message
f_tf_t - time (hours) of maximum 24-hour wind speed in 1200 UTC message
f_i - index of ranges of 2-minute wind speed attained during 24 hours ending at 0600 UTC and reported in 1200 UTC message